3.0.4.md

OpenAPI Specification

Version 3.0.4

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 RFC2119 RFC8174 when, and only when, they appear in all capitals, as shown here.

This document is licensed under The Apache License, Version 2.0.

Introduction

The OpenAPI Specification (OAS) defines a standard, language-agnostic interface to HTTP APIs which allows both humans and computers to discover and understand the capabilities of the service without access to source code, documentation, or through network traffic inspection. When properly defined, a consumer can understand and interact with the remote service with a minimal amount of implementation logic.

An OpenAPI Description can then be used by documentation generation tools to display the API, code generation tools to generate servers and clients in various programming languages, testing tools, and many other use cases.

For examples of OpenAPI usage and additional documentation, please visit [[?OpenAPI-Learn]].

For extension registries and other specifications published by the OpenAPI Initiative, as well as the authoritative rendering of this specification, please visit spec.openapis.org.

Definitions

OpenAPI Description

An OpenAPI Description (OAD) formally describes the surface of an API and its semantics. It is composed of an entry document, which must be an OpenAPI Document, and any/all of its referenced documents. An OAD uses and conforms to the OpenAPI Specification.

OpenAPI Document

An OpenAPI Document is a single JSON or YAML document that conforms to the OpenAPI Specification. An OpenAPI Document compatible with OAS 3.*.* contains a required openapi field which designates the version of the OAS that it uses.

Schema

A "schema" is a formal description of syntax and structure. This document serves as the schema for the OpenAPI Specification format; a non-authoritative JSON Schema based on this document is also provided on spec.openapis.org for informational purposes. This specification also uses schemas in the form of the Schema Object.

Object

When capitalized, the word "Object" refers to any of the Objects that are named by section headings in this document.

Path Templating

Path templating refers to the usage of template expressions, delimited by curly braces ({}), to mark a section of a URL path as replaceable using path parameters.

Each template expression in the path MUST correspond to a path parameter that is included in the Path Item itself and/or in each of the Path Item's Operations.

Media Types

Media type definitions are spread across several resources. The media type definitions SHOULD be in compliance with RFC6838.

Some examples of possible media type definitions:

  text/plain; charset=utf-8
  application/json
  application/vnd.github+json
  application/vnd.github.v3+json
  application/vnd.github.v3.raw+json
  application/vnd.github.v3.text+json
  application/vnd.github.v3.html+json
  application/vnd.github.v3.full+json
  application/vnd.github.v3.diff
  application/vnd.github.v3.patch

HTTP Status Codes

The HTTP Status Codes are used to indicate the status of the executed operation. Status codes SHOULD be selected from the available status codes registered in the IANA Status Code Registry.

Case Sensitivity

As most field names and values in the OpenAPI Specification are case-sensitive, this document endeavors to call out any case-insensitive names and values. However, the case sensitivity of field names and values that map directly to HTTP concepts follow the case sensitivity rules of HTTP, even if this document does not make a note of every concept.

Undefined and Implementation-Defined Behavior

This specification deems certain situations to have either undefined or implementation-defined behavior.

Behavior described as undefined is likely, at least in some circumstances, to result in outcomes that contradict the specification. This description is used when detecting the contradiction is impossible or impractical. Implementations MAY support undefined scenarios for historical reasons, including ambiguous text in prior versions of the specification. This support might produce correct outcomes in many cases, but relying on it is NOT RECOMMENDED as there is no guarantee that it will work across all tools or with future specification versions, even if those versions are otherwise strictly compatible with this one.

Behavior described as implementation-defined allows implementations to choose which of several different-but-compliant approaches to a requirement to implement. This documents ambiguous requirements that API description authors are RECOMMENDED to avoid in order to maximize interoperability. Unlike undefined behavior, it is safe to rely on implementation-defined behavior if and only if it can be guaranteed that all relevant tools support the same behavior.

Specification

Versions

The OpenAPI Specification is versioned using a major.minor.patch versioning scheme. The major.minor portion of the version string (for example 3.1) SHALL designate the OAS feature set. .patch versions address errors in, or provide clarifications to, this document, not the feature set. Tooling which supports OAS 3.1 SHOULD be compatible with all OAS 3.1.* versions. The patch version SHOULD NOT be considered by tooling, making no distinction between 3.1.0 and 3.1.1 for example.

Occasionally, non-backwards compatible changes may be made in minor versions of the OAS where impact is believed to be low relative to the benefit provided.

Format

An OpenAPI Document that conforms to the OpenAPI Specification is itself a JSON object, which may be represented either in JSON or YAML format.

For example, if a field has an array value, the JSON array representation will be used:

{
  "field": [1, 2, 3]
}

All field names in the specification are case sensitive. This includes all fields that are used as keys in a map, except where explicitly noted that keys are case insensitive.

The schema exposes two types of fields: fixed fields, which have a declared name, and patterned fields, which have a declared pattern for the field name.

Patterned fields MUST have unique names within the containing object.

In order to preserve the ability to round-trip between YAML and JSON formats, YAML version 1.2 is RECOMMENDED along with some additional constraints:

• Tags MUST be limited to those allowed by YAML's JSON schema ruleset, which defines a subset of the YAML syntax and is unrelated to [[JSON-Schema-05|JSON Schema]].
• Keys used in YAML maps MUST be limited to a scalar string, as defined by the YAML Failsafe schema ruleset.

Note: While APIs may be described by OpenAPI Descriptions in either YAML or JSON format, the API request and response bodies and other content are not required to be JSON or YAML.

OpenAPI Description Structure

An OpenAPI Description (OAD) MAY be made up of a single JSON or YAML document or be divided into multiple, connected parts at the discretion of the author. In the latter case, Reference Object and Path Item Object $ref fields, as well as the Link Object operationRef field, and the URI form of the Discriminator Object mapping field, are used to identify the referenced elements.

In a multi-document OAD, the document containing the OpenAPI Object where parsing begins is known as that OAD's entry document.

It is RECOMMENDED that the entry document of an OAD be named: openapi.json or openapi.yaml.

Structural Interoperability

JSON or YAML objects within an OAD are interpreted as specific Objects (such as Operation Objects, Response Objects, Reference Objects, etc.) based on their context. Depending on how references are arranged, a given JSON or YAML object can be interpreted in multiple different contexts:

• As the root object of the entry document, which is always interpreted as an OpenAPI Object
• As the Object type implied by its parent Object within the document
• As a reference target, with the Object type matching the reference source's context

If the same JSON/YAML object is parsed multiple times and the respective contexts require it to be parsed as different Object types, the resulting behavior is implementation defined, and MAY be treated as an error if detected. An example would be referencing an empty Schema Object under #/components/schemas where a Path Item Object is expected, as an empty object is valid for both types. For maximum interoperability, it is RECOMMENDED that OpenAPI Description authors avoid such scenarios.

Resolving Implicit Connections

Several features of this specification require resolution of non-URI-based connections to some other part of the OpenAPI Description (OAD).

These connections are unambiguously resolved in single-document OADs, but the resolution process in multi-document OADs is implementation-defined, within the constraints described in this section. In some cases, an unambiguous URI-based alternative is available, and OAD authors are RECOMMENDED to always use the alternative:

Source	Target	Alternative
Security Requirement Object {name}	Security Scheme Object name under the Components Object	n/a
Discriminator Object mapping (implicit, or explicit name syntax)	Schema Object name under the Components Object	mapping (explicit URI syntax)
Operation Object tags	Tag Object name (in the OpenAPI Object's tags array)	n/a
Link Object operationId	Path Item Object operationId	operationRef

A fifth implicit connection involves appending the templated URL paths of the Paths Object to the appropriate Server Object's url field. This is unambiguous because only the entry document's Paths Object contributes URLs to the described API.

It is RECOMMENDED to consider all Operation Objects from all parsed documents when resolving any Link Object operationId. This requires parsing all referenced documents prior to determining an operationId to be unresolvable.

The implicit connections in the Security Requirement Object and Discriminator Object rely on the component name, which is the name of the property holding the component in the appropriately typed sub-object of the Components Object. For example, the component name of the Schema Object at #/components/schemas/Foo is Foo. The implicit connection of tags in the Operation Object uses the name field of Tag Objects, which (like the Components Object) are found under the root OpenAPI Object. This means resolving component names and tag names both depend on starting from the correct OpenAPI Object.

For resolving component and tag name connections from a referenced (non-entry) document, it is RECOMMENDED that tools resolve from the entry document, rather than the current document. This allows Security Scheme Objects and Tag Objects to be defined next to the API's deployment information (the top-level array of Server Objects), and treated as an interface for referenced documents to access.

The interface approach can also work for Discriminator Objects and Schema Objects, but it is also possible to keep the Discriminator Object's behavior within a single document using the relative URI-reference syntax of mapping.

There are no URI-based alternatives for the Security Requirement Object or for the Operation Object's tags field. These limitations are expected to be addressed in a future release.

See Appendix F: Resolving Security Requirements in a Referenced Document for an example of the possible resolutions, including which one is recommended by this section. The behavior for Discrimator Object non-URI mappings and for the Operation Object's tags field operate on the same principles.

Note that no aspect of implicit connection resolution changes how URLs are resolved or restricts their possible targets.

Data Types

Data types in the OAS are based on the non-null types supported by the JSON Schema Validation Specification Draft Wright-00: "boolean", "object", "array", "number", "string", or "integer". See nullable for an alternative solution to "null" as a type. Models are defined using the Schema Object, which is an extended subset of JSON Schema Specification Draft Wright-00.

JSON Schema keywords and format values operate on JSON "instances" which may be one of the six JSON data types, "null", "boolean", "object", "array", "number", or "string", with certain keywords and formats only applying to a specific type. For example, the pattern keyword and the date-time format only apply to strings, and treat any instance of the other five types as automatically valid. This means JSON Schema keywords and formats do NOT implicitly require the expected type. Use the type keyword to explicitly constrain the type.

Note that the type keyword allows "integer" as a value for convenience, but keyword and format applicability does not recognize integers as being of a distinct JSON type from other numbers because [[RFC7159|JSON]] itself does not make that distinction. Since there is no distinct JSON integer type, JSON Schema defines integers mathematically. This means that both 1 and 1.0 are equivalent, and are both considered to be integers.

Data Type Format

As defined by the JSON Schema Validation specification, data types can have an optional modifier keyword: format. As described in that specification, format is treated as a non-validating annotation by default; the ability to validate format varies across implementations.

The OpenAPI Initiative also hosts a Format Registry for formats defined by OAS users and other specifications. Support for any registered format is strictly OPTIONAL, and support for one registered format does not imply support for any others.

Types that are not accompanied by a format keyword follow the type definition in the JSON Schema. Tools that do not recognize a specific format MAY default back to the type alone, as if the format is not specified. For the purpose of JSON Schema validation, each format should specify the set of JSON data types for which it applies. In this registry, these types are shown in the "JSON Data Type" column.

The formats defined by the OAS are:

format	JSON Data Type	Comments
int32	number	signed 32 bits
int64	number	signed 64 bits (a.k.a long)
float	number
double	number
byte	string	base64 encoded characters - RFC4648
binary	string	any sequence of octets
date	string	As defined by full-date - RFC3339
date-time	string	As defined by date-time - RFC3339
password	string	A hint to obscure the value.

Working with Binary Data

Two formats, binary and byte, describe different ways to work with binary data:

• binary is used where unencoded binary data is allowed, such as when sending a binary payload as an HTTP message body, or as part of a multipart/* payload that allows binary parts
• byte is used where binary data is embedded in a text-only format such as application/json or application/x-www-form-urlencoded

The maxLength keyword MAY be used to set an expected upper bound on the length of a streaming payload. The keyword can be applied to either string data, including encoded binary data, or to unencoded binary data. For unencoded binary, the length is the number of octets.

Note that the encoding indicated by byte, which inflates the size of data in order to represent it as 7-bit ASCII text, is unrelated to HTTP's Content-Encoding header, which indicates whether and how a message body has been compressed.

Rich Text Formatting

Throughout the specification description fields are noted as supporting CommonMark markdown formatting. Where OpenAPI tooling renders rich text it MUST support, at a minimum, markdown syntax as described by CommonMark 0.27. Tooling MAY choose to ignore some CommonMark or extension features to address security concerns.

While the framing of CommonMark 0.27 as a minimum requirement means that tooling MAY choose to implement extensions on top of it, note that any such extensions are by definition implementation-defined and will not be interoperable. OpenAPI Description authors SHOULD consider how text using such extensions will be rendered by tools that offer only the minimum support.

Relative References in URLs

Unless specified otherwise, all fields that are URLs MAY be relative references as defined by RFC3986.

Relative references are resolved using the URLs defined in the Server Object as a Base URI.

Relative references used in $ref are processed as per JSON Reference, using the URL of the current document as the base URI. See also the Reference Object.

It is implementation_defined whether the resolution of relative references in each of the operationRef field of the Link Object, the URI form of the mapping field of the Discriminator Object, the externalValue field of the Example Object, and the url fields of the External Documentation, Contact, and License Objects resolve by using the same process as $ref or by using the Server Object. For compatibility with future versions of this specification, the $ref process is RECOMMENDED for all of these fields.

Relative references in CommonMark hyperlinks are resolved in their rendered context, which might differ from the context of the API description.

Schema

This section describes the structure of the OpenAPI Description format. This text is the only normative description of the format. A JSON Schema is hosted on spec.openapis.org for informational purposes. If the JSON Schema differs from this section, then this section MUST be considered authoritative.

In the following description, if a field is not explicitly REQUIRED or described with a MUST or SHALL, it can be considered OPTIONAL.

OpenAPI Object

This is the root object of the OpenAPI Description.

Fixed Fields

Field Name	Type	Description
openapi	string	REQUIRED. This string MUST be the version number of the OpenAPI Specification that the OpenAPI Document uses. The openapi field SHOULD be used by tooling to interpret the OpenAPI Document. This is not related to the API info.version string.
info	Info Object	REQUIRED. Provides metadata about the API. The metadata MAY be used by tooling as required.
servers	[Server Object]	An array of Server Objects, which provide connectivity information to a target server. If the servers field is not provided, or is an empty array, the default value would be a Server Object with a url value of /.
paths	Paths Object	REQUIRED. The available paths and operations for the API.
components	Components Object	An element to hold various Objects for the OpenAPI Description.
security	[Security Requirement Object]	A declaration of which security mechanisms can be used across the API. The list of values includes alternative Security Requirement Objects that can be used. Only one of the Security Requirement Objects need to be satisfied to authorize a request. Individual operations can override this definition. The list can be incomplete, up to being empty or absent. To make security explicitly optional, an empty security requirement ({}) can be included in the array.
tags	[Tag Object]	A list of tags used by the OpenAPI Description with additional metadata. The order of the tags can be used to reflect on their order by the parsing tools. Not all tags that are used by the Operation Object must be declared. The tags that are not declared MAY be organized randomly or based on the tools' logic. Each tag name in the list MUST be unique.
externalDocs	External Documentation Object	Additional external documentation.

This object MAY be extended with Specification Extensions.

Info Object

The object provides metadata about the API. The metadata MAY be used by the clients if needed, and MAY be presented in editing or documentation generation tools for convenience.

Fixed Fields

Field Name	Type	Description
title	string	REQUIRED. The title of the API.
description	string	A description of the API. CommonMark syntax MAY be used for rich text representation.
termsOfService	string	A URL for the Terms of Service for the API. This MUST be in the form of a URL.
contact	Contact Object	The contact information for the exposed API.
license	License Object	The license information for the exposed API.
version	string	REQUIRED. The version of the OpenAPI Document (which is distinct from the OpenAPI Specification version or the version of the API being described or the version of the OpenAPI Description).

This object MAY be extended with Specification Extensions.

Info Object Example

{
  "title": "Example Pet Store App",
  "description": "This is an example server for a pet store.",
  "termsOfService": "https://example.com/terms/",
  "contact": {
    "name": "API Support",
    "url": "https://www.example.com/support",
    "email": "[email protected]"
  },
  "license": {
    "name": "Apache 2.0",
    "url": "https://www.apache.org/licenses/LICENSE-2.0.html"
  },
  "version": "1.0.1"
}

title: Example Pet Store App
description: This is an example server for a pet store.
termsOfService: https://example.com/terms/
contact:
  name: API Support
  url: https://www.example.com/support
  email: [email protected]
license:
  name: Apache 2.0
  url: https://www.apache.org/licenses/LICENSE-2.0.html
version: 1.0.1

Contact Object

Contact information for the exposed API.

Fixed Fields

Field Name	Type	Description
name	string	The identifying name of the contact person/organization.
url	string	The URL for the contact information. This MUST be in the form of a URL.
email	string	The email address of the contact person/organization. This MUST be in the form of an email address.

This object MAY be extended with Specification Extensions.

Contact Object Example

{
  "name": "API Support",
  "url": "https://www.example.com/support",
  "email": "[email protected]"
}

name: API Support
url: https://www.example.com/support
email: [email protected]

License Object

License information for the exposed API.

Fixed Fields

Field Name	Type	Description
name	string	REQUIRED. The license name used for the API.
url	string	A URL for the license used for the API. This MUST be in the form of a URL.

This object MAY be extended with Specification Extensions.

License Object Example

{
  "name": "Apache 2.0",
  "url": "https://www.apache.org/licenses/LICENSE-2.0.html"
}

name: Apache 2.0
url: https://www.apache.org/licenses/LICENSE-2.0.html

Server Object

An object representing a Server.

Fixed Fields

Field Name	Type	Description
url	string	REQUIRED. A URL to the target host. This URL supports Server Variables and MAY be relative, to indicate that the host location is relative to the location where the document containing the Server Object is being served. Variable substitutions will be made when a variable is named in {braces}.
description	string	An optional string describing the host designated by the URL. CommonMark syntax MAY be used for rich text representation.
variables	Map[string, Server Variable Object]	A map between a variable name and its value. The value is used for substitution in the server's URL template.

This object MAY be extended with Specification Extensions.

Server Object Example

A single server would be described as:

{
  "url": "https://development.gigantic-server.com/v1",
  "description": "Development server"
}

url: https://development.gigantic-server.com/v1
description: Development server

The following shows how multiple servers can be described, for example, at the OpenAPI Object's servers:

{
  "servers": [
    {
      "url": "https://development.gigantic-server.com/v1",
      "description": "Development server"
    },
    {
      "url": "https://staging.gigantic-server.com/v1",
      "description": "Staging server"
    },
    {
      "url": "https://api.gigantic-server.com/v1",
      "description": "Production server"
    }
  ]
}

servers:
  - url: https://development.gigantic-server.com/v1
    description: Development server
  - url: https://staging.gigantic-server.com/v1
    description: Staging server
  - url: https://api.gigantic-server.com/v1
    description: Production server

The following shows how variables can be used for a server configuration:

{
  "servers": [
    {
      "url": "https://{username}.gigantic-server.com:{port}/{basePath}",
      "description": "The production API server",
      "variables": {
        "username": {
          "default": "demo",
          "description": "A user-specific subdomain. Use `demo` for a free sandbox environment."
        },
        "port": {
          "enum": ["8443", "443"],
          "default": "8443"
        },
        "basePath": {
          "default": "v2"
        }
      }
    }
  ]
}

servers:
  - url: https://{username}.gigantic-server.com:{port}/{basePath}
    description: The production API server
    variables:
      username:
        # note! no enum here means it is an open value
        default: demo
        description: A user-specific subdomain. Use `demo` for a free sandbox environment.
      port:
        enum:
          - '8443'
          - '443'
        default: '8443'
      basePath:
        # open meaning there is the opportunity to use special base paths as assigned by the provider, default is `v2`
        default: v2

Server Variable Object

An object representing a Server Variable for server URL template substitution.

Fixed Fields

Field Name	Type	Description
enum	[string]	An enumeration of string values to be used if the substitution options are from a limited set. The array SHOULD NOT be empty.
default	string	REQUIRED. The default value to use for substitution, which SHALL be sent if an alternate value is not supplied. If the enum is defined, the value SHOULD exist in the enum's values. Note that this behavior is different from the Schema Object's default keyword, which documents the receiver's behavior rather than inserting the value into the data.
description	string	An optional description for the server variable. CommonMark syntax MAY be used for rich text representation.

This object MAY be extended with Specification Extensions.

Components Object

Holds a set of reusable objects for different aspects of the OAS. All objects defined within the Components Object will have no effect on the API unless they are explicitly referenced from outside the Components Object.

Fixed Fields

Field Name	Type	Description
schemas	Map[string, Schema Object | Reference Object]	An object to hold reusable Schema Objects.
responses	Map[string, Response Object | Reference Object]	An object to hold reusable Response Objects.
parameters	Map[string, Parameter Object | Reference Object]	An object to hold reusable Parameter Objects.
examples	Map[string, Example Object | Reference Object]	An object to hold reusable Example Objects.
requestBodies	Map[string, Request Body Object | Reference Object]	An object to hold reusable Request Body Objects.
headers	Map[string, Header Object | Reference Object]	An object to hold reusable Header Objects.
securitySchemes	Map[string, Security Scheme Object | Reference Object]	An object to hold reusable Security Scheme Objects.
links	Map[string, Link Object | Reference Object]	An object to hold reusable Link Objects.
callbacks	Map[string, Callback Object | Reference Object]	An object to hold reusable Callback Objects.

This object MAY be extended with Specification Extensions.

All the fixed fields declared above are objects that MUST use keys that match the regular expression: ^[a-zA-Z0-9\.\-_]+$.

Field Name Examples:

User
User_1
User_Name
user-name
my.org.User

Components Object Example

"components": {
  "schemas": {
    "GeneralError": {
      "type": "object",
      "properties": {
        "code": {
          "type": "integer",
          "format": "int32"
        },
        "message": {
          "type": "string"
        }
      }
    },
    "Category": {
      "type": "object",
      "properties": {
        "id": {
          "type": "integer",
          "format": "int64"
        },
        "name": {
          "type": "string"
        }
      }
    },
    "Tag": {
      "type": "object",
      "properties": {
        "id": {
          "type": "integer",
          "format": "int64"
        },
        "name": {
          "type": "string"
        }
      }
    }
  },
  "parameters": {
    "skipParam": {
      "name": "skip",
      "in": "query",
      "description": "number of items to skip",
      "required": true,
      "schema": {
        "type": "integer",
        "format": "int32"
      }
    },
    "limitParam": {
      "name": "limit",
      "in": "query",
      "description": "max records to return",
      "required": true,
      "schema" : {
        "type": "integer",
        "format": "int32"
      }
    }
  },
  "responses": {
    "NotFound": {
      "description": "Entity not found."
    },
    "IllegalInput": {
      "description": "Illegal input for operation."
    },
    "GeneralError": {
      "description": "General Error",
      "content": {
        "application/json": {
          "schema": {
            "$ref": "#/components/schemas/GeneralError"
          }
        }
      }
    }
  },
  "securitySchemes": {
    "api_key": {
      "type": "apiKey",
      "name": "api-key",
      "in": "header"
    },
    "petstore_auth": {
      "type": "oauth2",
      "flows": {
        "implicit": {
          "authorizationUrl": "https://example.org/api/oauth/dialog",
          "scopes": {
            "write:pets": "modify pets in your account",
            "read:pets": "read your pets"
          }
        }
      }
    }
  }
}

components:
  schemas:
    GeneralError:
      type: object
      properties:
        code:
          type: integer
          format: int32
        message:
          type: string
    Category:
      type: object
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
    Tag:
      type: object
      properties:
        id:
          type: integer
          format: int64
        name:
          type: string
  parameters:
    skipParam:
      name: skip
      in: query
      description: number of items to skip
      required: true
      schema:
        type: integer
        format: int32
    limitParam:
      name: limit
      in: query
      description: max records to return
      required: true
      schema:
        type: integer
        format: int32
  responses:
    NotFound:
      description: Entity not found.
    IllegalInput:
      description: Illegal input for operation.
    GeneralError:
      description: General Error
      content:
        application/json:
          schema:
            $ref: '#/components/schemas/GeneralError'
  securitySchemes:
    api_key:
      type: apiKey
      name: api-key
      in: header
    petstore_auth:
      type: oauth2
      flows:
        implicit:
          authorizationUrl: https://example.org/api/oauth/dialog
          scopes:
            write:pets: modify pets in your account
            read:pets: read your pets

Paths Object

Holds the relative paths to the individual endpoints and their operations. The path is appended to the URL from the Server Object in order to construct the full URL. The Paths Object MAY be empty, due to Access Control List (ACL) constraints.

Patterned Fields

Field Pattern	Type	Description
/{path}	Path Item Object	A relative path to an individual endpoint. The field name MUST begin with a forward slash (/). The path is appended (no relative URL resolution) to the expanded URL from the Server Object's url field in order to construct the full URL. Path templating is allowed. When matching URLs, concrete (non-templated) paths would be matched before their templated counterparts. Templated paths with the same hierarchy but different templated names MUST NOT exist as they are identical. In case of ambiguous matching, it's up to the tooling to decide which one to use.

This object MAY be extended with Specification Extensions.

Path Templating Matching

Assuming the following paths, the concrete definition, /pets/mine, will be matched first if used:

  /pets/{petId}
  /pets/mine

The following paths are considered identical and invalid:

  /pets/{petId}
  /pets/{name}

The following may lead to ambiguous resolution:

  /{entity}/me
  /books/{id}

Paths Object Example

{
  "/pets": {
    "get": {
      "description": "Returns all pets from the system that the user has access to",
      "responses": {
        "200": {
          "description": "A list of pets.",
          "content": {
            "application/json": {
              "schema": {
                "type": "array",
                "items": {
                  "$ref": "#/components/schemas/pet"
                }
              }
            }
          }
        }
      }
    }
  }
}

/pets:
  get:
    description: Returns all pets from the system that the user has access to
    responses:
      '200':
        description: A list of pets.
        content:
          application/json:
            schema:
              type: array
              items:
                $ref: '#/components/schemas/pet'

Path Item Object

Describes the operations available on a single path. A Path Item MAY be empty, due to ACL constraints. The path itself is still exposed to the documentation viewer but they will not know which operations and parameters are available.

Fixed Fields

Field Name	Type	Description
$ref	string	Allows for a referenced definition of this path item. The value MUST be in the form of a URL, and the referenced structure MUST be in the form of a Path Item Object. In case a Path Item Object field appears both in the defined object and the referenced object, the behavior is undefined. See the rules for resolving Relative References.
summary	string	An optional string summary, intended to apply to all operations in this path.
description	string	An optional string description, intended to apply to all operations in this path. CommonMark syntax MAY be used for rich text representation.
get	Operation Object	A definition of a GET operation on this path.
put	Operation Object	A definition of a PUT operation on this path.
post	Operation Object	A definition of a POST operation on this path.
delete	Operation Object	A definition of a DELETE operation on this path.
options	Operation Object	A definition of a OPTIONS operation on this path.
head	Operation Object	A definition of a HEAD operation on this path.
patch	Operation Object	A definition of a PATCH operation on this path.
trace	Operation Object	A definition of a TRACE operation on this path.
servers	[Server Object]	An alternative servers array to service all operations in this path. If a servers array is specified at the OpenAPI Object level, it will be overridden by this value.
parameters	[Parameter Object | Reference Object]	A list of parameters that are applicable for all the operations described under this path. These parameters can be overridden at the operation level, but cannot be removed there. The list MUST NOT include duplicated parameters. A unique parameter is defined by a combination of a name and location. The list can use the Reference Object to link to parameters that are defined in the OpenAPI Object's components.parameters.

This object MAY be extended with Specification Extensions.

Path Item Object Example

{
  "get": {
    "description": "Returns pets based on ID",
    "summary": "Find pets by ID",
    "operationId": "getPetsById",
    "responses": {
      "200": {
        "description": "pet response",
        "content": {
          "*/*": {
            "schema": {
              "type": "array",
              "items": {
                "$ref": "#/components/schemas/Pet"
              }
            }
          }
        }
      },
      "default": {
        "description": "error payload",
        "content": {
          "text/html": {
            "schema": {
              "$ref": "#/components/schemas/ErrorModel"
            }
          }
        }
      }
    }
  },
  "parameters": [
    {
      "name": "id",
      "in": "path",
      "description": "ID of pet to use",
      "required": true,
      "schema": {
        "type": "array",
        "items": {
          "type": "string"
        }
      },
      "style": "simple"
    }
  ]
}

get:
  description: Returns pets based on ID
  summary: Find pets by ID
  operationId: getPetsById
  responses:
    '200':
      description: pet response
      content:
        '*/*':
          schema:
            type: array
            items:
              $ref: '#/components/schemas/Pet'
    default:
      description: error payload
      content:
        text/html:
          schema:
            $ref: '#/components/schemas/ErrorModel'
parameters:
  - name: id
    in: path
    description: ID of pet to use
    required: true
    schema:
      type: array
      items:
        type: string
    style: simple

Operation Object

Describes a single API operation on a path.

Fixed Fields

Field Name	Type	Description
tags	[string]	A list of tags for API documentation control. Tags can be used for logical grouping of operations by resources or any other qualifier.
summary	string	A short summary of what the operation does.
description	string	A verbose explanation of the operation behavior. CommonMark syntax MAY be used for rich text representation.
externalDocs	External Documentation Object	Additional external documentation for this operation.
operationId	string	Unique string used to identify the operation. The id MUST be unique among all operations described in the API. The operationId value is case-sensitive. Tools and libraries MAY use the operationId to uniquely identify an operation, therefore, it is RECOMMENDED to follow common programming naming conventions.
parameters	[Parameter Object | Reference Object]	A list of parameters that are applicable for this operation. If a parameter is already defined in the Path Item, the new definition will override it but can never remove it. The list MUST NOT include duplicated parameters. A unique parameter is defined by a combination of a name and location. The list can use the Reference Object to link to parameters that are defined in the OpenAPI Object's components.parameters.
requestBody	Request Body Object | Reference Object	The request body applicable for this operation. The requestBody is only supported in HTTP methods where the HTTP 1.1 specification RFC7231 has explicitly defined semantics for request bodies. In other cases where the HTTP spec is vague (such as GET, HEAD and DELETE), requestBody SHALL be ignored by consumers.
responses	Responses Object	REQUIRED. The list of possible responses as they are returned from executing this operation.
callbacks	Map[string, Callback Object | Reference Object]	A map of possible out-of band callbacks related to the parent operation. The key is a unique identifier for the Callback Object. Each value in the map is a Callback Object that describes a request that may be initiated by the API provider and the expected responses.
deprecated	boolean	Declares this operation to be deprecated. Consumers SHOULD refrain from usage of the declared operation. Default value is false.
security	[Security Requirement Object]	A declaration of which security mechanisms can be used for this operation. The list of values includes alternative Security Requirement Objects that can be used. Only one of the Security Requirement Objects need to be satisfied to authorize a request. To make security optional, an empty security requirement ({}) can be included in the array. This definition overrides any declared top-level security. To remove a top-level security declaration, an empty array can be used.
servers	[Server Object]	An alternative servers array to service this operation. If a servers array is specified at the Path Item Object or OpenAPI Object level, it will be overridden by this value.

This object MAY be extended with Specification Extensions.

Operation Object Example

{
  "tags": ["pet"],
  "summary": "Updates a pet in the store with form data",
  "operationId": "updatePetWithForm",
  "parameters": [
    {
      "name": "petId",
      "in": "path",
      "description": "ID of pet that needs to be updated",
      "required": true,
      "schema": {
        "type": "string"
      }
    }
  ],
  "requestBody": {
    "content": {
      "application/x-www-form-urlencoded": {
        "schema": {
          "type": "object",
          "properties": {
            "name": {
              "description": "Updated name of the pet",
              "type": "string"
            },
            "status": {
              "description": "Updated status of the pet",
              "type": "string"
            }
          },
          "required": ["status"]
        }
      }
    }
  },
  "responses": {
    "200": {
      "description": "Pet updated.",
      "content": {
        "application/json": {},
        "application/xml": {}
      }
    },
    "405": {
      "description": "Method Not Allowed",
      "content": {
        "application/json": {},
        "application/xml": {}
      }
    }
  },
  "security": [
    {
      "petstore_auth": ["write:pets", "read:pets"]
    }
  ]
}

tags:
  - pet
summary: Updates a pet in the store with form data
operationId: updatePetWithForm
parameters:
  - name: petId
    in: path
    description: ID of pet that needs to be updated
    required: true
    schema:
      type: string
requestBody:
  content:
    application/x-www-form-urlencoded:
      schema:
        type: object
        properties:
          name:
            description: Updated name of the pet
            type: string
          status:
            description: Updated status of the pet
            type: string
        required:
          - status
responses:
  '200':
    description: Pet updated.
    content:
      application/json: {}
      application/xml: {}
  '405':
    description: Method Not Allowed
    content:
      application/json: {}
      application/xml: {}
security:
  - petstore_auth:
      - write:pets
      - read:pets

External Documentation Object

Allows referencing an external resource for extended documentation.

Fixed Fields

Field Name	Type	Description
description	string	A description of the target documentation. CommonMark syntax MAY be used for rich text representation.
url	string	REQUIRED. The URL for the target documentation. This MUST be in the form of a URL.

This object MAY be extended with Specification Extensions.

External Documentation Object Example

{
  "description": "Find more info here",
  "url": "https://example.com"
}

description: Find more info here
url: https://example.com

Parameter Object

Describes a single operation parameter.

A unique parameter is defined by a combination of a name and location.

See Appendix E for a detailed examination of percent-encoding concerns, including interactions with the application/x-www-form-urlencoded query string format.

Parameter Locations

There are four possible parameter locations specified by the in field:

• path - Used together with Path Templating, where the parameter value is actually part of the operation's URL. This does not include the host or base path of the API. For example, in /items/{itemId}, the path parameter is itemId.
• query - Parameters that are appended to the URL. For example, in /items?id=###, the query parameter is id.
• header - Custom headers that are expected as part of the request. Note that RFC7230 states header names are case insensitive.
• cookie - Used to pass a specific cookie value to the API.

Fixed Fields

The rules for serialization of the parameter are specified in one of two ways. Parameter Objects MUST include either a content field or a schema field, but not both. See Appendix B for a discussion of converting values of various types to string representations.

Common Fixed Fields

These fields MAY be used with either content or schema.

Field Name	Type	Description
name	string	REQUIRED. The name of the parameter. Parameter names are case sensitive. If in is "path", the name field MUST correspond to a template expression occurring within the path field in the Paths Object. See Path Templating for further information. If in is "header" and the name field is "Accept", "Content-Type" or "Authorization", the parameter definition SHALL be ignored. For all other cases, the name corresponds to the parameter name used by the in field.
in	string	REQUIRED. The location of the parameter. Possible values are "query", "header", "path" or "cookie".
description	string	A brief description of the parameter. This could contain examples of use. CommonMark syntax MAY be used for rich text representation.
required	boolean	Determines whether this parameter is mandatory. If the parameter location is "path", this field is REQUIRED and its value MUST be true. Otherwise, the field MAY be included and its default value is false.
deprecated	boolean	Specifies that a parameter is deprecated and SHOULD be transitioned out of usage. Default value is false.
allowEmptyValue	boolean	If true, clients MAY pass a zero-length string value in place of parameters that would otherwise be omitted entirely, which the server SHOULD interpret as the parameter being unused. Default value is false. If style is used, and if behavior is n/a (cannot be serialized), the value of allowEmptyValue SHALL be ignored. Interactions between this field and the parameter's Schema Object are implementation-defined. This field is valid only for query parameters. Use of this field is NOT RECOMMENDED, and it is likely to be removed in a later revision.

This object MAY be extended with Specification Extensions.

Note that while "Cookie" as a name is not forbidden if in is "header", the effect of defining a cookie parameter that way is undefined; use in: "cookie" instead.

Fixed Fields for use with schema

For simpler scenarios, a schema and style can describe the structure and syntax of the parameter. When example or examples are provided in conjunction with the schema field, the example SHOULD match the specified schema and follow the prescribed serialization strategy for the parameter. The example and examples fields are mutually exclusive, and if either is present it SHALL override any example in the schema.

Serializing with schema is NOT RECOMMENDED for in: "cookie" parameters, in: "header" parameters that use HTTP header parameters (name=value pairs following a ;) in their values, or in: "header" parameters where values might have non-URL-safe characters; see Appendix D for details.

Field Name	Type	Description
style	string	Describes how the parameter value will be serialized depending on the type of the parameter value. Default values (based on value of in): for "query" - "form"; for "path" - "simple"; for "header" - "simple"; for "cookie" - "form".
explode	boolean	When this is true, parameter values of type array or object generate separate parameters for each value of the array or key-value pair of the map. For other types of parameters this field has no effect. When style is "form", the default value is true. For all other styles, the default value is false. Note that despite false being the default for deepObject, the combination of false with deepObject is undefined.
allowReserved	boolean	When this is true, parameter values are serialized using reserved expansion, as defined by RFC6570, which allows RFC3986's reserved character set, as well as percent-encoded triples, to pass through unchanged, while still percent-encoding all other disallowed characters (including % outside of percent-encoded triples). Applications are still responsible for percent-encoding reserved characters that are not allowed in the query string ([, ], #), or have a special meaning in application/x-www-form-urlencoded (-, &, +); see Appendices C and E for details. This field only applies to parameters with an in value of query. The default value is false.
schema	Schema Object | Reference Object	The schema defining the type used for the parameter.
example	Any	Example of the parameter's potential value; see Working With Examples.
examples	Map[ string, Example Object | Reference Object]	Examples of the parameter's potential value; see Working With Examples.

See also Appendix C: Using RFC6570-Based Serialization for additional guidance.

Fixed Fields for use with content

For more complex scenarios, the content field can define the media type and schema of the parameter, as well as give examples of its use. Using content with a text/plain media type is RECOMMENDED for in: "header" and in: "cookie" parameters where the schema strategy is not appropriate.

Field Name	Type	Description
content	Map[string, Media Type Object]	A map containing the representations for the parameter. The key is the media type and the value describes it. The map MUST only contain one entry.

Style Values

In order to support common ways of serializing simple parameters, a set of style values are defined.

style	type	in	Comments
matrix	primitive, array, object	path	Path-style parameters defined by RFC6570
label	primitive, array, object	path	Label style parameters defined by RFC6570
simple	primitive, array, object	path, header	Simple style parameters defined by RFC6570. This option replaces collectionFormat with a csv value from OpenAPI 2.0.
form	primitive, array, object	query, cookie	Form style parameters defined by RFC6570. This option replaces collectionFormat with a csv (when explode is false) or multi (when explode is true) value from OpenAPI 2.0.
spaceDelimited	array, object	query	Space separated array values or object properties and values. This option replaces collectionFormat equal to ssv from OpenAPI 2.0.
pipeDelimited	array, object	query	Pipe separated array values or object properties and values. This option replaces collectionFormat equal to pipes from OpenAPI 2.0.
deepObject	object	query	Allows objects with scalar properties to be represented using form parameters. The representation of array or object properties is not defined.

See Appendix E for a discussion of percent-encoding, including when delimiters need to be percent-encoded and options for handling collisions with percent-encoded data.

Style Examples

Assume a parameter named color has one of the following values:

   string -> "blue"
   array -> ["blue", "black", "brown"]
   object -> { "R": 100, "G": 200, "B": 150 }

The following table shows examples, as would be shown with the example or examples keywords, of the different serializations for each value.

• The value empty denotes the empty string, and is unrelated to the allowEmptyValue field
• The behavior of combinations marked n/a is undefined
• The undefined column replaces the empty column in previous versions of this specification in order to better align with RFC6570 terminology, which describes certain values including but not limited to null as "undefined" values with special handling; notably, the empty string is not undefined
• For form and the non-RFC6570 query string styles spaceDelimited, pipeDelimited, and deepObject, each example is shown prefixed with ? as if it were the only query parameter; see Appendix C for more information on constructing query strings from multiple parameters, and Appendix D for warnings regarding form and cookie parameters
• Note that the ? prefix is not appropriate for serializing application/x-www-form-urlencoded HTTP message bodies, and MUST be stripped or (if constructing the string manually) not added when used in that context; see the Encoding Object for more information
• The examples are percent-encoded as required by RFC6570 and RFC3986; see Appendix E for a thorough discussion of percent-encoding concerns, including why unencoded | (%7C), [ (%5B), and ] (%5D) seem to work in some environments despite not being compliant.

style	explode	undefined	string	array	object
matrix	false	;color	;color=blue	;color=blue,black,brown	;color=R,100,G,200,B,150
matrix	true	;color	;color=blue	;color=blue;color=black;color=brown	;R=100;G=200;B=150
label	false	.	.blue	.blue,black,brown	.R,100,G,200,B,150
label	true	.	.blue	.blue.black.brown	.R=100.G=200.B=150
simple	false	empty	blue	blue,black,brown	R,100,G,200,B,150
simple	true	empty	blue	blue,black,brown	R=100,G=200,B=150
form	false	?color=	?color=blue	?color=blue,black,brown	?color=R,100,G,200,B,150
form	true	?color=	?color=blue	?color=blue&color=black&color=brown	?R=100&G=200&B=150
spaceDelimited	false	n/a	n/a	?color=blue%20black%20brown	?color=R%20100%20G%20200%20B%20150
spaceDelimited	true	n/a	n/a	n/a	n/a
pipeDelimited	false	n/a	n/a	?color=blue%7Cblack%7Cbrown	?color=R%7C100%7CG%7C200%7CB%7C150
pipeDelimited	true	n/a	n/a	n/a	n/a
deepObject	false	n/a	n/a	n/a	n/a
deepObject	true	n/a	n/a	n/a	?color%5BR%5D=100&color%5BG%5D=200&color%5BB%5D=150

Parameter Object Examples

A header parameter with an array of 64-bit integer numbers:

{
  "name": "token",
  "in": "header",
  "description": "token to be passed as a header",
  "required": true,
  "schema": {
    "type": "array",
    "items": {
      "type": "integer",
      "format": "int64"
    }
  },
  "style": "simple"
}

name: token
in: header
description: token to be passed as a header
required: true
schema:
  type: array
  items:
    type: integer
    format: int64
style: simple

A path parameter of a string value:

{
  "name": "username",
  "in": "path",
  "description": "username to fetch",
  "required": true,
  "schema": {
    "type": "string"
  }
}

name: username
in: path
description: username to fetch
required: true
schema:
  type: string

An optional query parameter of a string value, allowing multiple values by repeating the query parameter:

{
  "name": "id",
  "in": "query",
  "description": "ID of the object to fetch",
  "required": false,
  "schema": {
    "type": "array",
    "items": {
      "type": "string"
    }
  },
  "style": "form",
  "explode": true
}

name: id
in: query
description: ID of the object to fetch
required: false
schema:
  type: array
  items:
    type: string
style: form
explode: true

A free-form query parameter, allowing undefined parameters of a specific type:

{
  "in": "query",
  "name": "freeForm",
  "schema": {
    "type": "object",
    "additionalProperties": {
      "type": "integer"
    }
  },
  "style": "form"
}

in: query
name: freeForm
schema:
  type: object
  additionalProperties:
    type: integer
style: form

A complex parameter using content to define serialization:

{
  "in": "query",
  "name": "coordinates",
  "content": {
    "application/json": {
      "schema": {
        "type": "object",
        "required": ["lat", "long"],
        "properties": {
          "lat": {
            "type": "number"
          },
          "long": {
            "type": "number"
          }
        }
      }
    }
  }
}

in: query
name: coordinates
content:
  application/json:
    schema:
      type: object
      required:
        - lat
        - long
      properties:
        lat:
          type: number
        long:
          type: number

Request Body Object

Describes a single request body.

Fixed Fields

Field Name	Type	Description
description	string	A brief description of the request body. This could contain examples of use. CommonMark syntax MAY be used for rich text representation.
content	Map[string, Media Type Object]	REQUIRED. The content of the request body. The key is a media type or media type range and the value describes it. For requests that match multiple keys, only the most specific key is applicable. e.g. "text/plain" overrides "text/*"
required	boolean	Determines if the request body is required in the request. Defaults to false.

This object MAY be extended with Specification Extensions.

Request Body Examples

A request body with a referenced schema definition.

{
  "description": "user to add to the system",
  "content": {
    "application/json": {
      "schema": {
        "$ref": "#/components/schemas/User"
      },
      "examples": {
        "user": {
          "summary": "User Example",
          "externalValue": "https://foo.bar/examples/user-example.json"
        }
      }
    },
    "application/xml": {
      "schema": {
        "$ref": "#/components/schemas/User"
      },
      "examples": {
        "user": {
          "summary": "User example in XML",
          "externalValue": "https://foo.bar/examples/user-example.xml"
        }
      }
    },
    "text/plain": {
      "examples": {
        "user": {
          "summary": "User example in Plain text",
          "externalValue": "https://foo.bar/examples/user-example.txt"
        }
      }
    },
    "*/*": {
      "examples": {
        "user": {
          "summary": "User example in other format",
          "externalValue": "https://foo.bar/examples/user-example.whatever"
        }
      }
    }
  }
}

description: user to add to the system
content:
  application/json:
    schema:
      $ref: '#/components/schemas/User'
    examples:
      user:
        summary: User example
        externalValue: https://foo.bar/examples/user-example.json
  application/xml:
    schema:
      $ref: '#/components/schemas/User'
    examples:
      user:
        summary: User example in XML
        externalValue: https://foo.bar/examples/user-example.xml
  text/plain:
    examples:
      user:
        summary: User example in plain text
        externalValue: https://foo.bar/examples/user-example.txt
  '*/*':
    examples:
      user:
        summary: User example in other format
        externalValue: https://foo.bar/examples/user-example.whatever

Media Type Object

Each Media Type Object provides schema and examples for the media type identified by its key.

When example or examples are provided, the example SHOULD match the specified schema and be in the correct format as specified by the media type and its encoding. The example and examples fields are mutually exclusive, and if either is present it SHALL override any example in the schema. See Working With Examples for further guidance regarding the different ways of specifying examples, including non-JSON/YAML values.

Fixed Fields

Field Name	Type	Description
schema	Schema Object | Reference Object	The schema defining the content of the request, response, parameter, or header.
example	Any	Example of the media type; see Working With Examples.
examples	Map[ string, Example Object | Reference Object]	Examples of the media type; see Working With Examples.
encoding	Map[string, Encoding Object]	A map between a property name and its encoding information. The key, being the property name, MUST exist in the schema as a property. The encoding field SHALL only apply to Request Body Objects, and only when the media type is multipart or application/x-www-form-urlencoded. If no Encoding Object is provided for a property, the behavior is determined by the default values documented for the Encoding Object.

This object MAY be extended with Specification Extensions.

Media Type Examples

{
  "application/json": {
    "schema": {
      "$ref": "#/components/schemas/Pet"
    },
    "examples": {
      "cat": {
        "summary": "An example of a cat",
        "value": {
          "name": "Fluffy",
          "petType": "Cat",
          "color": "White",
          "gender": "male",
          "breed": "Persian"
        }
      },
      "dog": {
        "summary": "An example of a dog with a cat's name",
        "value": {
          "name": "Puma",
          "petType": "Dog",
          "color": "Black",
          "gender": "Female",
          "breed": "Mixed"
        }
      },
      "frog": {
        "$ref": "#/components/examples/frog-example"
      }
    }
  }
}

application/json:
  schema:
    $ref: '#/components/schemas/Pet'
  examples:
    cat:
      summary: An example of a cat
      value:
        name: Fluffy
        petType: Cat
        color: White
        gender: male
        breed: Persian
    dog:
      summary: An example of a dog with a cat's name
      value:
        name: Puma
        petType: Dog
        color: Black
        gender: Female
        breed: Mixed
    frog:
      $ref: '#/components/examples/frog-example'

Considerations for File Uploads

In contrast to OpenAPI 2.0, file input/output content in OpenAPI 3 is described with the same semantics as any other schema type. Specifically:

# content transferred in binary (octet-stream):
schema:
  type: string
  format: binary

These examples apply to either input payloads of file uploads or response payloads.

A requestBody for submitting a file in a POST operation may look like the following example:

requestBody:
  content:
    application/octet-stream:
      schema:
        # a binary file of any type
        type: string
        format: binary

In addition, specific media types MAY be specified:

# multiple, specific media types may be specified:
requestBody:
  content:
    # a binary file of type png or jpeg
    'image/jpeg':
      schema:
        type: string
        format: binary
    'image/png':
      schema:
        type: string
        format: binary

To upload multiple files, a multipart media type MUST be used as shown under Example: Multipart Form with Multiple Files.

Support for x-www-form-urlencoded Request Bodies

See Encoding the x-www-form-urlencoded Media Type for guidance and examples, both with and without the encoding field.

Special Considerations for multipart Content

See Encoding multipart Media Types for further guidance and examples, both with and without the encoding field.

Encoding Object

A single encoding definition applied to a single schema property. See Appendix B for a discussion of converting values of various types to string representations.

Properties are correlated with multipart parts using the name parameter of Content-Disposition: form-data, and with application/x-www-form-urlencoded using the query string parameter names. In both cases, their order is implementation-defined.

See Appendix E for a detailed examination of percent-encoding concerns for form media types.

Fixed Fields

Common Fixed Fields

These fields MAY be used either with or without the RFC6570-style serialization fields defined in the next section below.

Field Name	Type	Description
contentType	string	The Content-Type for encoding a specific property. The value is a comma-separated list, each element of which is either a specific media type (e.g. image/png) or a wildcard media type (e.g. image/*). Default value depends on the property type as shown in the table below.
headers	Map[string, Header Object | Reference Object]	A map allowing additional information to be provided as headers. Content-Type is described separately and SHALL be ignored in this section. This field SHALL be ignored if the request body media type is not a multipart.

This object MAY be extended with Specification Extensions.

The default values for contentType are as follows, where an n/a in the format column means that the presence or value of format is irrelevant:

type	format	Default contentType
string	binary or byte	application/octet-stream
string	none, or any except binary or byte	text/plain
number, integer, or boolean	n/a	text/plain
object	n/a	application/json
array	n/a	according to the type and format of the items schema

Determining how to handle null values if nullable: true is present depends on how null values are being serialized. If null values are entirely omitted, then the contentType is irrelevant. See Appendix B for a discussion of data type conversion options.

Fixed Fields for RFC6570-style Serialization

Field Name	Type	Description
style	string	Describes how a specific property value will be serialized depending on its type. See Parameter Object for details on the style field. The behavior follows the same values as query parameters, including default values. Note that the initial ? used in query strings is not used in application/x-www-form-urlencoded message bodies, and MUST be removed (if using an RFC6570 implementation) or simply not added (if constructing the string manually). This field SHALL be ignored if the request body media type is not application/x-www-form-urlencoded.
explode	boolean	When this is true, property values of type array or object generate separate parameters for each value of the array, or key-value-pair of the map. For other types of properties this field has no effect. When style is "form", the default value is true. For all other styles, the default value is false. Note that despite false being the default for deepObject, the combination of false with deepObject is undefined. This field SHALL be ignored if the request body media type is not application/x-www-form-urlencoded.
allowReserved	boolean	When this is true, parameter values are serialized using reserved expansion, as defined by RFC6570, which allows RFC3986's reserved character set, as well as percent-encoded triples, to pass through unchanged, while still percent-encoding all other disallowed characters (including % outside of percent-encoded triples). Applications are still responsible for percent-encoding reserved characters that are not allowed in the query string ([, ], #), or have a special meaning in application/x-www-form-urlencoded (-, &, +); see Appendices C and E for details. The default value is false. This field SHALL be ignored if the request body media type is not application/x-www-form-urlencoded.

See also Appendix C: Using RFC6570-Based Serialization for additional guidance.

The role of contentType with application/x-www-form-urlencoded request bodies was not described in detail in version 3.0.3 and earlier of this specification. To match the intent of these fields and be compatible with version 3.1 of this specification, it is RECOMMENDED that whenever any of style, explode, or allowReserved are present with an explicit value:

• The value of contentType, whether it is explicitly defined or has the default value, is to be ignored
• If any of style, explode, or allowReserved are not present with explicit values, then they are to be treated as if they were present with their default values

However, if all three of style, explode, and allowReserved fields are absent, it is RECOMMENDED that:

• All three keywords are to be entirely ignored, rather than treated as having their default values
• Encoding is to be based on contentType alone, whether it is present with an explicit value or absent and treated as having its default value

Note that the presence of at least one of style, explode, or allowReserved with an explicit value is equivalent to using schema with in: "query" Parameter Objects. The absence of all three of those fields is the equivalent of using content, but with the media type specified in contentType rather than through a Media Type Object.

Encoding the x-www-form-urlencoded Media Type

To submit content using form url encoding via RFC1866, use the application/x-www-form-urlencoded media type in the Media Type Object under the Request Body Object. This configuration means that the request body MUST be encoded per RFC1866 when passed to the server, after any complex objects have been serialized to a string representation.

See Appendix E for a detailed examination of percent-encoding concerns for form media types.

Example: URL Encoded Form with JSON Values

When there is no encoding field, the serialization strategy is based on the Encoding Object's default values:

requestBody:
  content:
    application/x-www-form-urlencoded:
      schema:
        type: object
        properties:
          id:
            type: string
            format: uuid
          address:
            # complex types are stringified to support RFC 1866
            type: object
            properties: {}

With this example, consider an id of f81d4fae-7dec-11d0-a765-00a0c91e6bf6 and a US-style address (with ZIP+4) as follows:

{
  "streetAddress": "123 Example Dr.",
  "city": "Somewhere",
  "state": "CA",
  "zip": "99999+1234"
}

Assuming the most compact representation of the JSON value (with unnecessary whitespace removed), we would expect to see the following request body, where space characters have been replaced with + and +, ", {, and } have been percent-encoded to %2B, %22, %7B, and %7D, respectively:

id=f81d4fae-7dec-11d0-a765-00a0c91e6bf6&address=%7B%22streetAddress%22:%22123+Example+Dr.%22,%22city%22:%22Somewhere%22,%22state%22:%22CA%22,%22zip%22:%2299999%2B1234%22%7D

Note that the id keyword is treated as text/plain per the Encoding Object's default behavior, and is serialized as-is. If it were treated as application/json, then the serialized value would be a JSON string including quotation marks, which would be percent-encoded as %22.

Here is the id parameter (without address) serialized as application/json instead of text/plain, and then encoded per RFC1866:

id=%22f81d4fae-7dec-11d0-a765-00a0c91e6bf6%22

Example: URL Encoded Form with Binary Values

Note that application/x-www-form-urlencoded is a text format, which requires base64-encoding any binary data:

requestBody:
  content:
    application/x-www-form-urlencoded:
      schema:
        type: object
        properties:
          name:
            type: string
          icon:
            # The default with "format: byte" is application/octet-stream,
            # so we need to set image media type(s) in the Encoding Object.
            type: string
            format: byte
  encoding:
    icon:
      contentType: image/png, image/jpeg

Given a name of example and a solid red 2x2-pixel PNG for icon, this would produce a request body of:

name=example&icon=iVBORw0KGgoAAAANSUhEUgAAAAIAAAACCAIAAAD91JpzAAAABGdBTUEAALGPC%2FxhBQAAADhlWElmTU0AKgAAAAgAAYdpAAQAAAABAAAAGgAAAAAAAqACAAQAAAABAAAAAqADAAQAAAABAAAAAgAAAADO0J6QAAAAEElEQVQIHWP8zwACTGCSAQANHQEDqtPptQAAAABJRU5ErkJggg%3D%3D

Note that this base64-encoded value had to be futher percent-encoded, replacing / with %2F and each of two final = padding characters with %3D. Some base64-decoding implementations may be able to use the string without the padding per RFC4648. However, this is not guaranteed and the value would still need to be percent-decoded due to the %2F.

Encoding multipart Media Types

It is common to use multipart/form-data as a Content-Type when transferring forms as request bodies. In contrast to OpenAPI 2.0, a schema is REQUIRED to define the input parameters to the operation when using multipart content. This supports complex structures as well as supporting mechanisms for multiple file uploads.

The form-data disposition and its name parameter are mandatory for multipart/form-data (RFC7578). Array properties are handled by applying the same name to multiple parts, as is recommended by RFC7578 for supplying multiple values per form field. See RFC7578 for guidance regarding non-ASCII part names.

Various other multipart types, most notable multipart/mixed (RFC2046) neither require nor forbid specific Content-Disposition values, which means care must be taken to ensure that any values used are supported by all relevant software. It is not currently possible to correlate schema properties with unnamed, ordered parts in media types such as multipart/mixed, but implementations MAY choose to support such types when Content-Disposition: form-data is used with a name parameter.

Note that there are significant restrictions on what headers can be used with multipart media types in general (RFC2046) and multi-part/form-data in particular (RFC7578).

Note also that Content-Transfer-Encoding is deprecated for multipart/form-data (RFC7578) where binary data is supported, as it is in HTTP.

Using format: "byte" for a multipart field is equivalent to specifying an Encoding Object with a headers field containing Content-Transfer-Encoding with a schema that requires the value base64. If format: "byte" is used for a multipart field that has an Encoding Object with a headers field containing Content-Transfer-Encoding with a schema that disallows base64, the result is undefined for serialization and parsing.

Per the JSON Schema specification, contentMediaType without contentEncoding present is treated as if contentEncoding: "identity" were present. While useful for embedding text documents such as text/html into JSON strings, it is not useful for a multipart/form-data part, as it just causes the document to be treated as text/plain instead of its actual media type. Use the Encoding Object without contentMediaType if no contentEncoding is required.

See Appendix E for a detailed examination of percent-encoding concerns for form media types.

Example: Basic Multipart Form

When the encoding field is not used, the encoding is determined by the Encoding Object's defaults:

requestBody:
  content:
    multipart/form-data:
      schema:
        type: object
        properties:
          id:
            # default for primitives without a special format is text/plain
            type: string
            format: uuid
          profileImage:
            # default for string with binary format is `application/octet-stream`
            type: string
            format: binary
          addresses:
            # default for arrays is based on the type in the `items`
            # subschema, which is an object, so `application/json`
            type: array
            items:
              $ref: '#/components/schemas/Address'

Example: Multipart Form with Encoding Objects

Using encoding, we can set more specific types for binary data, or non-JSON formats for complex values. We can also describe headers for each part:

requestBody:
  content:
    multipart/form-data:
      schema:
        type: object
        properties:
          id:
            # default is `text/plain`
            type: string
            format: uuid
          addresses:
            # default based on the `items` subschema would be
            # `application/json`, but we want these address objects
            # serialized as `application/xml` instead
            description: addresses in XML format
            type: array
            items:
              $ref: '#/components/schemas/Address'
          profileImage:
            # default is application/octet-stream, but we can declare
            # a more specific image type or types
            type: string
            format: binary
      encoding:
        addresses:
          # require XML Content-Type in utf-8 encoding
          # This is applied to each address part corresponding
          # to each address in he array
          contentType: application/xml; charset=utf-8
        profileImage:
          # only accept png or jpeg
          contentType: image/png, image/jpeg
          headers:
            X-Rate-Limit-Limit:
              description: The number of allowed requests in the current period
              schema:
                type: integer

Example: Multipart Form with Multiple Files

In accordance with RFC7578, multiple files for a single form field are uploaded using the same name (file in this example) for each file's part:

requestBody:
  content:
    multipart/form-data:
      schema:
        properties:
          # The property name 'file' will be used for all files.
          file:
            type: array
            items:
              type: string
              format: binary

Responses Object

A container for the expected responses of an operation. The container maps a HTTP response code to the expected response.

The documentation is not necessarily expected to cover all possible HTTP response codes because they may not be known in advance. However, documentation is expected to cover a successful operation response and any known errors.

The default MAY be used as a default Response Object for all HTTP codes that are not covered individually by the Responses Object.

The Responses Object MUST contain at least one response code, and if only one response code is provided it SHOULD be the response for a successful operation call.

Fixed Fields

Field Name	Type	Description
default	Response Object | Reference Object	The documentation of responses other than the ones declared for specific HTTP response codes. Use this field to cover undeclared responses. A Reference Object can link to a response that the OpenAPI Object's components.responses section defines.

Patterned Fields

Field Pattern	Type	Description
HTTP Status Code	Response Object | Reference Object	Any HTTP status code can be used as the property name, but only one property per code, to describe the expected response for that HTTP status code. A Reference Object can link to a response that is defined in the OpenAPI Object's components.responses section. This field MUST be enclosed in quotation marks (for example, "200") for compatibility between JSON and YAML. To define a range of response codes, this field MAY contain the uppercase wildcard character X. For example, 2XX represents all response codes between 200 and 299. Only the following range definitions are allowed: 1XX, 2XX, 3XX, 4XX, and 5XX. If a response is defined using an explicit code, the explicit code definition takes precedence over the range definition for that code.

This object MAY be extended with Specification Extensions.

Responses Object Example

A 200 response for a successful operation and a default response for others (implying an error):

{
  "200": {
    "description": "a pet to be returned",
    "content": {
      "application/json": {
        "schema": {
          "$ref": "#/components/schemas/Pet"
        }
      }
    }
  },
  "default": {
    "description": "Unexpected error",
    "content": {
      "application/json": {
        "schema": {
          "$ref": "#/components/schemas/ErrorModel"
        }
      }
    }
  }
}

'200':
  description: a pet to be returned
  content:
    application/json:
      schema:
        $ref: '#/components/schemas/Pet'
default:
  description: Unexpected error
  content:
    application/json:
      schema:
        $ref: '#/components/schemas/ErrorModel'

Response Object

Describes a single response from an API operation, including design-time, static links to operations based on the response.

Fixed Fields

Field Name	Type	Description
description	string	REQUIRED. A description of the response. CommonMark syntax MAY be used for rich text representation.
headers	Map[string, Header Object | Reference Object]	Maps a header name to its definition. RFC7230 states header names are case insensitive. If a response header is defined with the name "Content-Type", it SHALL be ignored.
content	Map[string, Media Type Object]	A map containing descriptions of potential response payloads. The key is a media type or media type range and the value describes it. For responses that match multiple keys, only the most specific key is applicable. e.g. "text/plain" overrides "text/*"
links	Map[string, Link Object | Reference Object]	A map of operations links that can be followed from the response. The key of the map is a short name for the link, following the naming constraints of the names for Component Objects.

This object MAY be extended with Specification Extensions.

Response Object Examples

Response of an array of a complex type:

{
  "description": "A complex object array response",
  "content": {
    "application/json": {
      "schema": {
        "type": "array",
        "items": {
          "$ref": "#/components/schemas/VeryComplexType"
        }
      }
    }
  }
}

description: A complex object array response
content:
  application/json:
    schema:
      type: array
      items:
        $ref: '#/components/schemas/VeryComplexType'

Response with a string type:

{
  "description": "A simple string response",
  "content": {
    "text/plain": {
      "schema": {
        "type": "string"
      }
    }
  }
}

description: A simple string response
content:
  text/plain:
    schema:
      type: string

Plain text response with headers:

{
  "description": "A simple string response",
  "content": {
    "text/plain": {
      "schema": {
        "type": "string"
      },
      "example": "whoa!"
    }
  },
  "headers": {
    "X-Rate-Limit-Limit": {
      "description": "The number of allowed requests in the current period",
      "schema": {
        "type": "integer"
      }
    },
    "X-Rate-Limit-Remaining": {
      "description": "The number of remaining requests in the current period",
      "schema": {
        "type": "integer"
      }
    },
    "X-Rate-Limit-Reset": {
      "description": "The number of seconds left in the current period",
      "schema": {
        "type": "integer"
      }
    }
  }
}

description: A simple string response
content:
  text/plain:
    schema:
      type: string
    example: 'whoa!'
headers:
  X-Rate-Limit-Limit:
    description: The number of allowed requests in the current period
    schema:
      type: integer
  X-Rate-Limit-Remaining:
    description: The number of remaining requests in the current period
    schema:
      type: integer
  X-Rate-Limit-Reset:
    description: The number of seconds left in the current period
    schema:
      type: integer

Response with no return value:

{
  "description": "object created"
}

description: object created

Callback Object

A map of possible out-of band callbacks related to the parent operation. Each value in the map is a Path Item Object that describes a set of requests that may be initiated by the API provider and the expected responses. The key value used to identify the Path Item Object is an expression, evaluated at runtime, that identifies a URL to use for the callback operation.

Patterned Fields

Field Pattern	Type	Description
{expression}	Path Item Object	A Path Item Object used to define a callback request and expected responses. A complete example is available.

This object MAY be extended with Specification Extensions.

Key Expression

The key that identifies the Path Item Object is a runtime expression that can be evaluated in the context of a runtime HTTP request/response to identify the URL to be used for the callback request. A simple example might be $request.body#/url. However, using a runtime expression the complete HTTP message can be accessed. This includes accessing any part of a body that a JSON Pointer RFC6901 can reference.

For example, given the following HTTP request:

POST /subscribe/myevent?queryUrl=https://clientdomain.com/stillrunning HTTP/1.1
Host: example.org
Content-Type: application/json
Content-Length: 188

{
  "failedUrl": "https://clientdomain.com/failed",
  "successUrls": [
    "https://clientdomain.com/fast",
    "https://clientdomain.com/medium",
    "https://clientdomain.com/slow"
  ]
}

resulting in:

201 Created
Location: https://example.org/subscription/1

The following examples show how the various expressions evaluate, assuming the callback operation has a path parameter named eventType and a query parameter named queryUrl.

Expression	Value
$url	https://example.org/subscribe/myevent?queryUrl=https://clientdomain.com/stillrunning
$method	POST
$request.path.eventType	myevent
$request.query.queryUrl	https://clientdomain.com/stillrunning
$request.header.content-type	application/json
$request.body#/failedUrl	https://clientdomain.com/failed
$request.body#/successUrls/1	https://clientdomain.com/medium
$response.header.Location	https://example.org/subscription/1

Callback Object Examples

The following example uses the user provided queryUrl query string parameter to define the callback URL. This is an example of how to use a Callback Object to describe a WebHook callback that goes with the subscription operation to enable registering for the WebHook.

myCallback:
  '{$request.query.queryUrl}':
    post:
      requestBody:
        description: Callback payload
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/SomePayload'
      responses:
        '200':
          description: callback successfully processed

The following example shows a callback where the server is hard-coded, but the query string parameters are populated from the id and email property in the request body.

transactionCallback:
  'http://notificationServer.com?transactionId={$request.body#/id}&email={$request.body#/email}':
    post:
      requestBody:
        description: Callback payload
        content:
          application/json:
            schema:
              $ref: '#/components/schemas/SomePayload'
      responses:
        '200':
          description: callback successfully processed

Example Object

An object grouping an internal or external example value with basic summary and description metadata. This object is typically used in fields named examples (plural), and is a referenceable alternative to older example (singular) fields that do not support referencing or metadata.

Examples allow demonstration of the usage of properties, parameters and objects within OpenAPI.

Fixed Fields

Field Name	Type	Description
summary	string	Short description for the example.
description	string	Long description for the example. CommonMark syntax MAY be used for rich text representation.
value	Any	Embedded literal example. The value field and externalValue field are mutually exclusive. To represent examples of media types that cannot naturally represented in JSON or YAML, use a string value to contain the example, escaping where necessary.
externalValue	string	A URL that points to the literal example. This provides the capability to reference examples that cannot easily be included in JSON or YAML documents. The value field and externalValue field are mutually exclusive. See the rules for resolving Relative References.

This object MAY be extended with Specification Extensions.

In all cases, the example value SHOULD be compatible with the schema of its associated value. Tooling implementations MAY choose to validate compatibility automatically, and reject the example value(s) if incompatible.

Working with Examples

Example Objects can be used in both Parameter Objects and Media Type Objects. In both objects, this is done through the examples (plural) field. However, there are two other ways to provide examples: The example (singular) field that is mutually exclusive with examples in both objects, and the example (singular) field in the Schema Object that appears in the schema field of both objects. Each of these fields has slightly different considerations.

The Schema Object's example field is used to show example values without regard to how they might be formatted as parameters or within media type representations.

The mutually exclusive fields in the Parameter or Media Type Objects are used to show example values which SHOULD both match the schema and be formatted as they would appear as a serialized parameter or within a media type representation. The exact serialization and encoding is determined by various fields in the Parameter Object, or in the Media Type Object's Encoding Object. Because examples using these fields represent the final serialized form of the data, they SHALL override any example in the corresponding Schema Object.

The singular example field in the Parameter or Media Type Object is concise and convenient for simple examples, but does not offer any other advantages over using Example Objects under examples.

Some examples cannot be represented directly in JSON or YAML. For all three ways of providing examples, these can be shown as string values with any escaping necessary to make the string valid in the JSON or YAML format of documents that comprise the OpenAPI Description. With the Example Object, such values can alternatively be handled through the externalValue field.

Example Object Examples

In a request body:

requestBody:
  content:
    'application/json':
      schema:
        $ref: '#/components/schemas/Address'
      examples:
        foo:
          summary: A foo example
          value:
            foo: bar
        bar:
          summary: A bar example
          value:
            bar: baz
    application/xml:
      examples:
        xmlExample:
          summary: This is an example in XML
          externalValue: https://example.org/examples/address-example.xml
    text/plain:
      examples:
        textExample:
          summary: This is a text example
          externalValue: https://foo.bar/examples/address-example.txt

In a parameter:

parameters:
  - name: zipCode
    in: query
    schema:
      type: string
      format: zip-code
    examples:
      zip-example:
        $ref: '#/components/examples/zip-example'

In a response:

responses:
  '200':
    description: your car appointment has been booked
    content:
      application/json:
        schema:
          $ref: '#/components/schemas/SuccessResponse'
        examples:
          confirmation-success:
            $ref: '#/components/examples/confirmation-success'

Two different uses of JSON strings:

First, a request or response body that is just a JSON string (not an object containing a string):

"application/json": {
  "schema": {
    "type": "string"
  },
  "examples": {
    "jsonBody": {
      "description": "A body of just the JSON string \"json\"",
      "value": "json"
    }
  }
}

application/json:
  schema:
    type: string
  examples:
    jsonBody:
      description: 'A body of just the JSON string "json"'
      value: json

In the above example, we can just show the JSON string (or any JSON value) as-is, rather than stuffing a serialized JSON value into a JSON string, which would have looked like "\"json\"".

In contrast, a JSON string encoded inside of a URL-style form body:

"application/x-www-form-urlencoded": {
  "schema": {
    "type": "object",
    "properties": {
      "jsonValue": {
        "type": "string"
      }
    }
  },
  "encoding": {
    "jsonValue": {
      "contentType": "application/json"
    }
  },
  "examples": {
    "jsonFormValue": {
      "description": "The JSON string \"json\" as a form value",
      "value": "jsonValue=%22json%22"
    }
  }
}

application/x-www-form-urlencoded:
  schema:
    type: object
    properties:
      jsonValue:
        type: string
  encoding:
    jsonValue:
      contentType: application/json
  examples:
    jsonFormValue:
      description: 'The JSON string "json" as a form value'
      value: jsonValue=%22json%22

In this example, the JSON string had to be serialized before encoding it into the URL form value, so the example includes the quotation marks that are part of the JSON serialization, which are then URL percent-encoded.

Link Object

The Link Object represents a possible design-time link for a response. The presence of a link does not guarantee the caller's ability to successfully invoke it, rather it provides a known relationship and traversal mechanism between responses and other operations.

Unlike dynamic links (i.e. links provided in the response payload), the OAS linking mechanism does not require link information in the runtime response.

For computing links and providing instructions to execute them, a runtime expression is used for accessing values in an operation and using them as parameters while invoking the linked operation.

Fixed Fields

Field Name	Type	Description
operationRef	string	A URI reference to an OAS operation. This field is mutually exclusive of the operationId field, and MUST point to an Operation Object.
operationId	string	The name of an existing, resolvable OAS operation, as defined with a unique operationId. This field is mutually exclusive of the operationRef field.
parameters	Map[string, Any | {expression}]	A map representing parameters to pass to an operation as specified with operationId or identified via operationRef. The key is the parameter name to be used (optionally qualified with the parameter location, e.g. path.id for an id parameter in the path), whereas the value can be a constant or an expression to be evaluated and passed to the linked operation.
requestBody	Any | {expression}	A literal value or {expression} to use as a request body when calling the target operation.
description	string	A description of the link. CommonMark syntax MAY be used for rich text representation.
server	Server Object	A server object to be used by the target operation.

This object MAY be extended with Specification Extensions.

A linked operation MUST be identified using either an operationRef or operationId. The identified or reference operation MUST be unique, and in the case of an operationId, it MUST be resolved within the scope of the OpenAPI Description (OAD). Because of the potential for name clashes, the operationRef syntax is preferred for multi-document OADs. However, because use of an operation depends on its URL path template in the Paths Object, operations from any Path Item Object that is referenced multiple times within the OAD cannot be resolved unambiguously. In such ambiguous cases, the resulting behavior is implementation-defined and MAY result in an error.

Note that it is not possible to provide a constant value to parameters that matches the syntax of a runtime expression. It is possible to have ambiguous parameter names, e.g. name: "id", in: "path" and name: "path.id", in: "query"; this is NOT RECOMMENDED and the behavior is implementation-defined, however implementations SHOULD prefer the qualified interpretation (path.id as a path parameter), as the names can always be qualified to disambiguate them (e.g. using query.path.id for the query parameter).

Examples

Computing a link from a request operation where the $request.path.id is used to pass a request parameter to the linked operation.

paths:
  /users/{id}:
    parameters:
      - name: id
        in: path
        required: true
        description: the user identifier, as userId
        schema:
          type: string
    get:
      responses:
        '200':
          description: the user being returned
          content:
            application/json:
              schema:
                type: object
                properties:
                  uuid: # the unique user id
                    type: string
                    format: uuid
          links:
            address:
              # the target link operationId
              operationId: getUserAddress
              parameters:
                # get the `id` field from the request path parameter named `id`
                userid: $request.path.id
  # the path item of the linked operation
  /users/{userid}/address:
    parameters:
      - name: userid
        in: path
        required: true
        description: the user identifier, as userId
        schema:
          type: string
    # linked operation
    get:
      operationId: getUserAddress
      responses:
        '200':
          description: the user's address

When a runtime expression fails to evaluate, no parameter value is passed to the target operation.

Values from the response body can be used to drive a linked operation.

links:
  address:
    operationId: getUserAddressByUUID
    parameters:
      # get the `uuid` field from the `uuid` field in the response body
      userUuid: $response.body#/uuid

Clients follow all links at their discretion. Neither permissions nor the capability to make a successful call to that link is guaranteed solely by the existence of a relationship.

operationRef Examples

As references to operationId MAY NOT be possible (the operationId is an optional field in an Operation Object), references MAY also be made through a relative operationRef:

links:
  UserRepositories:
    # returns array of '#/components/schemas/repository'
    operationRef: '#/paths/~12.0~1repositories~1%7Busername%7D/get'
    parameters:
      username: $response.body#/username

or a URI operationRef:

links:
  UserRepositories:
    # returns array of '#/components/schemas/repository'
    operationRef: https://na2.gigantic-server.com/#/paths/~12.0~1repositories~1%7Busername%7D/get
    parameters:
      username: $response.body#/username

Note that in the use of operationRef the escaped forward-slash is necessary when using JSON Pointer, and it is necessary to URL-encode { and } as %7B and %7D, respectively, when using JSON Pointer as URI fragments.

Runtime Expressions

Runtime expressions allow defining values based on information that will only be available within the HTTP message in an actual API call. This mechanism is used by Link Objects and Callback Objects.

The runtime expression is defined by the following ABNF syntax

    expression = "$url" / "$method" / "$statusCode" / "$request." source / "$response." source
    source     = header-reference / query-reference / path-reference / body-reference
    header-reference = "header." token
    query-reference  = "query." name
    path-reference   = "path." name
    body-reference   = "body" ["#" json-pointer ]
    json-pointer    = *( "/" reference-token )
    reference-token = *( unescaped / escaped )
    unescaped       = %x00-2E / %x30-7D / %x7F-10FFFF
                    ; %x2F ('/') and %x7E ('~') are excluded from 'unescaped'
    escaped         = "~" ( "0" / "1" )
                    ; representing '~' and '/', respectively
    name = *( CHAR )
    token = 1*tchar
    tchar = "!" / "#" / "$" / "%" / "&" / "'" / "*" / "+" / "-" / "."
          / "^" / "_" / "`" / "|" / "~" / DIGIT / ALPHA

Here, json-pointer is taken from RFC6901, char from RFC7159 and token from RFC7230.

The name identifier is case-sensitive, whereas token is not.

The table below provides examples of runtime expressions and examples of their use in a value:

Examples

Source Location	example expression	notes
HTTP Method	$method	The allowable values for the $method will be those for the HTTP operation.
Requested media type	$request.header.accept
Request parameter	$request.path.id	Request parameters MUST be declared in the parameters section of the parent operation or they cannot be evaluated. This includes request headers.
Request body property	$request.body#/user/uuid	In operations which accept payloads, references may be made to portions of the requestBody or the entire body.
Request URL	$url
Response value	$response.body#/status	In operations which return payloads, references may be made to portions of the response body or the entire body.
Response header	$response.header.Server	Single header values only are available

Runtime expressions preserve the type of the referenced value. Expressions can be embedded into string values by surrounding the expression with {} curly braces.

Header Object

Describes a single header for HTTP responses and for individual parts in multipart representations; see the relevant Response Object and Encoding Object documentation for restrictions on which headers can be described.

The Header Object follows the structure of the Parameter Object, including determining its serialization strategy based on whether schema or content is present, with the following changes:

1. name MUST NOT be specified, it is given in the corresponding headers map.
2. in MUST NOT be specified, it is implicitly in header.
3. All traits that are affected by the location MUST be applicable to a location of header (for example, style). This means that allowEmptyValue and allowReserved MUST NOT be used, and style, if used, MUST be limited to "simple".

Fixed Fields

Common Fixed Fields

These fields MAY be used with either content or schema.

Field Name	Type	Description
description	string	A brief description of the header. This could contain examples of use. CommonMark syntax MAY be used for rich text representation.
required	boolean	Determines whether this header is mandatory. The default value is false.
deprecated	boolean	Specifies that the header is deprecated and SHOULD be transitioned out of usage. Default value is false.

This object MAY be extended with Specification Extensions.

Fixed Fields for use with schema

For simpler scenarios, a schema and style can describe the structure and syntax of the header. When example or examples are provided in conjunction with the schema field, the example MUST follow the prescribed serialization strategy for the header.

Serializing with schema is NOT RECOMMENDED for headers with parameters (name=value pairs following a ;) in their values, or where values might have non-URL-safe characters; see Appendix D for details.

When example or examples are provided in conjunction with the schema field, the example SHOULD match the specified schema and follow the prescribed serialization strategy for the header. The example and examples fields are mutually exclusive, and if either is present it SHALL override any example in the schema.

Field Name	Type	Description
style	string	Describes how the header value will be serialized. The default (and only legal value for headers) is "simple".
explode	boolean	When this is true, header values of type array or object generate a single header whose value is a comma-separated list of the array items or key-value pairs of the map, see Style Examples. For other data types this field has no effect. The default value is false.
schema	Schema Object | Reference Object	The schema defining the type used for the header.
example	Any	Example of the header's potential value; see Working With Examples.
examples	Map[ string, Example Object | Reference Object]	Examples of the header's potential value; see Working With Examples.

See also Appendix C: Using RFC6570-Based Serialization for additional guidance.

Fixed Fields for use with content

For more complex scenarios, the content field can define the media type and schema of the header, as well as give examples of its use. Using content with a text/plain media type is RECOMMENDED for headers where the schema strategy is not appropriate.

Field Name	Type	Description
content	Map[string, Media Type Object]	A map containing the representations for the header. The key is the media type and the value describes it. The map MUST only contain one entry.

Header Object Example

A simple header of type integer:

"X-Rate-Limit-Limit": {
  "description": "The number of allowed requests in the current period",
  "schema": {
    "type": "integer"
  }
}

X-Rate-Limit-Limit:
  description: The number of allowed requests in the current period
  schema:
    type: integer

Requiring that a strong ETag header (with a value starting with " rather than W/) is present. Note the use of content, because using schema and style would require the " to be percent-encoded as %22:

"ETag": {
  "required": true,
  "content": {
    "text/plain": {
      "schema": {
        "type": "string",
        "pattern": "^\""
      }
    }
  }
}

ETag:
  required: true
  content:
    text/plain:
      schema:
        type: string
        pattern: ^"

Tag Object

Adds metadata to a single tag that is used by the Operation Object. It is not mandatory to have a Tag Object per tag defined in the Operation Object instances.

Fixed Fields

Field Name	Type	Description
name	string	REQUIRED. The name of the tag.
description	string	A description for the tag. CommonMark syntax MAY be used for rich text representation.
externalDocs	External Documentation Object	Additional external documentation for this tag.

This object MAY be extended with Specification Extensions.

Tag Object Example

{
  "name": "pet",
  "description": "Pets operations"
}

name: pet
description: Pets operations

Reference Object

A simple object to allow referencing other components in the OpenAPI Description, internally and externally.

The Reference Object is defined by JSON Reference and follows the same structure, behavior and rules.

For this specification, reference resolution is accomplished as defined by the JSON Reference specification and not by the JSON Schema specification.

Fixed Fields

Field Name	Type	Description
$ref	string	REQUIRED. The reference string.

This object cannot be extended with additional properties, and any properties added SHALL be ignored.

Reference Object Example

{
  "$ref": "#/components/schemas/Pet"
}

$ref: '#/components/schemas/Pet'

Relative Schema Document Example

{
  "$ref": "Pet.json"
}

$ref: Pet.yaml

Relative Documents with Embedded Schema Example

{
  "$ref": "definitions.json#/Pet"
}

$ref: definitions.yaml#/Pet

Schema Object

The Schema Object allows the definition of input and output data types. These types can be objects, but also primitives and arrays. This object is an extended subset of the [[JSON-Schema-05|JSON Schema Specification Draft Wright-00]].

For more information about the keywords, see JSON Schema Core and JSON Schema Validation. Unless stated otherwise, the keyword definitions follow those of JSON Schema and do not add any additional semantics.

JSON Schema Keywords

The following keywords are taken directly from the JSON Schema definition and follow the same specifications:

• title
• multipleOf
• maximum
• exclusiveMaximum
• minimum
• exclusiveMinimum
• maxLength
• minLength
• pattern (This string SHOULD be a valid regular expression, according to the Ecma-262 Edition 5.1 regular expression dialect)
• maxItems
• minItems
• uniqueItems
• maxProperties
• minProperties
• required
• enum

The following keywords are taken from the JSON Schema definition but their definitions were adjusted to the OpenAPI Specification.

• type - Value MUST be a string. Multiple types via an array are not supported.
• allOf - Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
• oneOf - Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
• anyOf - Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
• not - Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema.
• items - Value MUST be an object and not an array. Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema. items MUST be present if type is "array".
• properties - Property definitions MUST be a Schema Object and not a standard JSON Schema (inline or referenced).
• additionalProperties - Value can be boolean or object. Inline or referenced schema MUST be of a Schema Object and not a standard JSON Schema. Consistent with JSON Schema, additionalProperties defaults to true.
• description - CommonMark syntax MAY be used for rich text representation.
• format - See Data Type Formats for further details. While relying on JSON Schema's defined formats, the OAS offers a few additional predefined formats.
• default - The default value represents what would be assumed by the consumer of the input as the value of the schema if one is not provided. Unlike JSON Schema, the value MUST conform to the defined type for the Schema Object defined at the same level. For example, if type is "string", then default can be "foo" but cannot be 1.

Alternatively, any time a Schema Object can be used, a Reference Object can be used in its place. This allows referencing definitions instead of defining them inline.

Additional keywords defined by the JSON Schema specification that are not mentioned here are strictly unsupported.

Other than the JSON Schema subset fields, the following fields MAY be used for further schema documentation:

Fixed Fields

Field Name	Type	Description
nullable	boolean	This keyword only takes effect if type is explicitly defined within the same Schema Object. A true value indicates that both null values and values of the type specified by type are allowed. Other Schema Object constraints retain their defined behavior, and therefore may disallow the use of null as a value. A false value leaves the specified or default type unmodified. The default value is false.
discriminator	Discriminator Object	Adds support for polymorphism. The discriminator is used to determine which of a set of schemas a payload is expected to satisfy. See Composition and Inheritance for more details.
readOnly	boolean	Relevant only for Schema Object properties definitions. Declares the property as "read only". This means that it MAY be sent as part of a response but SHOULD NOT be sent as part of the request. If the property is marked as readOnly being true and is in the required list, the required will take effect on the response only. A property MUST NOT be marked as both readOnly and writeOnly being true. Default value is false.
writeOnly	boolean	Relevant only for Schema Object properties definitions. Declares the property as "write only". Therefore, it MAY be sent as part of a request but SHOULD NOT be sent as part of the response. If the property is marked as writeOnly being true and is in the required list, the required will take effect on the request only. A property MUST NOT be marked as both readOnly and writeOnly being true. Default value is false.
xml	XML Object	This MAY be used only on property schemas. It has no effect on root schemas. Adds additional metadata to describe the XML representation of this property.
externalDocs	External Documentation Object	Additional external documentation for this schema.
example	Any	A free-form field to include an example of an instance for this schema. To represent examples that cannot be naturally represented in JSON or YAML, a string value can be used to contain the example with escaping where necessary.
deprecated	boolean	Specifies that a schema is deprecated and SHOULD be transitioned out of usage. Default value is false.

This object MAY be extended with Specification Extensions.

Composition and Inheritance (Polymorphism)

The OpenAPI Specification allows combining and extending model definitions using the allOf keyword of JSON Schema, in effect offering model composition. allOf takes an array of object definitions that are validated independently but together compose a single object.

While composition offers model extensibility, it does not imply a hierarchy between the models. To support polymorphism, the OpenAPI Specification adds the discriminator field. When used, the discriminator indicates the name of the property that hints which schema definition is expected to validate the structure of the model. As such, the discriminator field MUST be a required field. There are two ways to define the value of a discriminator for an inheriting instance.

• Use the schema name.
• Override the schema name by overriding the property with a new value. If a new value exists, this takes precedence over the schema name.

XML Modeling

The xml field allows extra definitions when translating the JSON definition to XML. The XML Object contains additional information about the available options.

Schema Object Examples

Primitive Example

{
  "type": "string",
  "format": "email"
}

type: string
format: email

Simple Model

{
  "type": "object",
  "required": ["name"],
  "properties": {
    "name": {
      "type": "string"
    },
    "address": {
      "$ref": "#/components/schemas/Address"
    },
    "age": {
      "type": "integer",
      "format": "int32",
      "minimum": 0
    }
  }
}

type: object
required:
  - name
properties:
  name:
    type: string
  address:
    $ref: '#/components/schemas/Address'
  age:
    type: integer
    format: int32
    minimum: 0

Model with Map/Dictionary Properties

For a simple string to string mapping:

{
  "type": "object",
  "additionalProperties": {
    "type": "string"
  }
}

type: object
additionalProperties:
  type: string

For a string to model mapping:

{
  "type": "object",
  "additionalProperties": {
    "$ref": "#/components/schemas/ComplexModel"
  }
}

type: object
additionalProperties:
  $ref: '#/components/schemas/ComplexModel'

Model with Example

{
  "type": "object",
  "properties": {
    "id": {
      "type": "integer",
      "format": "int64"
    },
    "name": {
      "type": "string"
    }
  },
  "required": ["name"],
  "example": {
    "name": "Puma",
    "id": 1
  }
}

type: object
properties:
  id:
    type: integer
    format: int64
  name:
    type: string
required:
  - name
example:
  name: Puma
  id: 1

Models with Composition

{
  "components": {
    "schemas": {
      "ErrorModel": {
        "type": "object",
        "required": ["message", "code"],
        "properties": {
          "message": {
            "type": "string"
          },
          "code": {
            "type": "integer",
            "minimum": 100,
            "maximum": 600
          }
        }
      },
      "ExtendedErrorModel": {
        "allOf": [
          {
            "$ref": "#/components/schemas/ErrorModel"
          },
          {
            "type": "object",
            "required": ["rootCause"],
            "properties": {
              "rootCause": {
                "type": "string"
              }
            }
          }
        ]
      }
    }
  }
}

components:
  schemas:
    ErrorModel:
      type: object
      required:
        - message
        - code
      properties:
        message:
          type: string
        code:
          type: integer
          minimum: 100
          maximum: 600
    ExtendedErrorModel:
      allOf:
        - $ref: '#/components/schemas/ErrorModel'
        - type: object
          required:
            - rootCause
          properties:
            rootCause:
              type: string

Models with Polymorphism Support

{
  "components": {
    "schemas": {
      "Pet": {
        "type": "object",
        "discriminator": {
          "propertyName": "petType"
        },
        "properties": {
          "name": {
            "type": "string"
          },
          "petType": {
            "type": "string"
          }
        },
        "required": ["name", "petType"]
      },
      "Cat": {
        "description": "A representation of a cat. Note that `Cat` will be used as the discriminating value.",
        "allOf": [
          {
            "$ref": "#/components/schemas/Pet"
          },
          {
            "type": "object",
            "properties": {
              "huntingSkill": {
                "type": "string",
                "description": "The measured skill for hunting",
                "default": "lazy",
                "enum": ["clueless", "lazy", "adventurous", "aggressive"]
              }
            },
            "required": ["huntingSkill"]
          }
        ]
      },
      "Dog": {
        "description": "A representation of a dog. Note that `Dog` will be used as the discriminating value.",
        "allOf": [
          {
            "$ref": "#/components/schemas/Pet"
          },
          {
            "type": "object",
            "properties": {
              "packSize": {
                "type": "integer",
                "format": "int32",
                "description": "the size of the pack the dog is from",
                "default": 0,
                "minimum": 0
              }
            },
            "required": ["packSize"]
          }
        ]
      }
    }
  }
}

components:
  schemas:
    Pet:
      type: object
      discriminator:
        propertyName: petType
      properties:
        name:
          type: string
        petType:
          type: string
      required:
        - name
        - petType
    Cat: # "Cat" will be used as the discriminating value
      description: A representation of a cat
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            huntingSkill:
              type: string
              description: The measured skill for hunting
              enum:
                - clueless
                - lazy
                - adventurous
                - aggressive
          required:
            - huntingSkill
    Dog: # "Dog" will be used as the discriminating value
      description: A representation of a dog
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          properties:
            packSize:
              type: integer
              format: int32
              description: the size of the pack the dog is from
              default: 0
              minimum: 0
          required:
            - packSize

Discriminator Object

When request bodies or response payloads may be one of a number of different schemas, a Discriminator Object gives a hint about the expected schema of the document. This hint can be used to aid in serialization, deserialization, and validation. The Discriminator Object does this by implicitly or explicitly associating the possible values of a named property with alternative schemas.

Note that discriminator MUST NOT change the validation outcome of the schema.

Fixed Fields

Field Name	Type	Description
propertyName	string	REQUIRED. The name of the property in the payload that will hold the discriminating value. This property SHOULD be required in the payload schema, as the behavior when the property is absent is undefined.
mapping	Map[string, string]	An object to hold mappings between payload values and schema names or URI references.

Conditions for Using the Discriminator Object

The Discriminator Object is legal only when using one of the composite keywords oneOf, anyOf, allOf.

In both the oneOf and anyOf use cases, where those keywords are adjacent to discriminator, all possible schemas MUST be listed explicitly.

To avoid redundancy, the discriminator MAY be added to a parent schema definition, and all schemas building on the parent schema via an allOf construct may be used as an alternate schema. It is implementation-defined as to whether all named Schema Objects under the Components Object, or only those that are otherwise directly referenced are searched for allOf references to the parent schema. However, it is RECOMMENDED to search all named schemas in the Components Object because it is common with the allOf usage for other parts of the API to only directly reference the parent schema.

The allOf form of discriminator is only useful for non-validation use cases; validation with the parent schema with this form of discriminator does not perform a search for child schemas or use them in validation in any way. This is because discriminator cannot change the validation outcome, and no standard JSON Schema keyword connects the parent schema to the child schemas.

The behavior of any configuration of oneOf, anyOf, allOf and discriminator that is not described above is undefined.

Options for Mapping Values to Schemas

The value of the property named in propertyName is used as the name of the associated schema under the Components Object, unless a mapping is present for that value. The mapping entry maps a specific property value to either a different schema component name, or to a schema identified by a URI. When using implicit or explicit schema component names, inline oneOf or anyOf subschemas are not considered. The behavior of a mapping value that is both a valid schema name and a valid relative URI reference is implementation-defined, but it is RECOMMENDED that it be treated as a schema name. To ensure that an ambiguous value (e.g. "foo") is treated as a relative URI reference by all implementations, authors MUST prefix it with the "." path segment (e.g. "./foo").

Mapping keys MUST be string values, but tooling MAY convert response values to strings for comparison. However, the exact nature of such conversions are implementation-defined.

Examples

For these examples, assume all schemas are in the entry document of the OAD; for handling of discriminator in referenced documents see Resolving Implicit Connections.

In OAS 3.0, a response payload MAY be described to be exactly one of any number of types:

MyResponseType:
  oneOf:
    - $ref: '#/components/schemas/Cat'
    - $ref: '#/components/schemas/Dog'
    - $ref: '#/components/schemas/Lizard'

which means the payload MUST, by validation, match exactly one of the schemas described by Cat, Dog, or Lizard. Deserialization of a oneOf can be a costly operation, as it requires determining which schema matches the payload and thus should be used in deserialization. This problem also exists for anyOf schemas. A discriminator MAY be used as a "hint" to improve the efficiency of selection of the matching schema. The discriminator field cannot change the validation result of the oneOf, it can only help make the deserialization more efficient and provide better error messaging. We can specify the exact field that tells us which schema is expected to match the instance:

MyResponseType:
  oneOf:
    - $ref: '#/components/schemas/Cat'
    - $ref: '#/components/schemas/Dog'
    - $ref: '#/components/schemas/Lizard'
  discriminator:
    propertyName: petType

The expectation now is that a property with name petType MUST be present in the response payload, and the value will correspond to the name of a schema defined in the OpenAPI Description. Thus the response payload:

{
  "id": 12345,
  "petType": "Cat"
}

will indicate that the Cat schema is expected to match this payload.

In scenarios where the value of the discriminator field does not match the schema name or implicit mapping is not possible, an optional mapping definition MAY be used:

MyResponseType:
  oneOf:
    - $ref: '#/components/schemas/Cat'
    - $ref: '#/components/schemas/Dog'
    - $ref: '#/components/schemas/Lizard'
    - $ref: https://gigantic-server.com/schemas/Monster/schema.json
  discriminator:
    propertyName: petType
    mapping:
      dog: '#/components/schemas/Dog'
      monster: https://gigantic-server.com/schemas/Monster/schema.json

Here the discriminating value of dog will map to the schema #/components/schemas/Dog, rather than the default (implicit) value of #/components/schemas/dog. If the discriminating value does not match an implicit or explicit mapping, no schema can be determined and validation SHOULD fail.

When used in conjunction with the anyOf construct, the use of the discriminator can avoid ambiguity for serializers/deserializers where multiple schemas may satisfy a single payload.

This example shows the allOf usage, which avoids needing to reference all child schemas in the parent:

components:
  schemas:
    Pet:
      type: object
      required:
        - petType
      properties:
        petType:
          type: string
      discriminator:
        propertyName: petType
        mapping:
          dog: Dog
    Cat:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Cat`
          properties:
            name:
              type: string
    Dog:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Dog`
          properties:
            bark:
              type: string
    Lizard:
      allOf:
        - $ref: '#/components/schemas/Pet'
        - type: object
          # all other properties specific to a `Lizard`
          properties:
            lovesRocks:
              type: boolean

Validated against the Pet schema, a payload like this:

{
  "petType": "Cat",
  "name": "Misty"
}

will indicate that the #/components/schemas/Cat schema is expected to match. Likewise this payload:

{
  "petType": "dog",
  "bark": "soft"
}

will map to #/components/schemas/Dog because the dog entry in the mapping element maps to Dog which is the schema name for #/components/schemas/Dog.

XML Object

A metadata object that allows for more fine-tuned XML model definitions.

When using arrays, XML element names are not inferred (for singular/plural forms) and the name field SHOULD be used to add that information. See examples for expected behavior.

Fixed Fields

Field Name	Type	Description
name	string	Replaces the name of the element/attribute used for the described schema property. When defined within items, it will affect the name of the individual XML elements within the list. When defined alongside type being "array" (outside the items), it will affect the wrapping element if and only if wrapped is true. If wrapped is false, it will be ignored.
namespace	string	The URI of the namespace definition. Value MUST be in the form of a non-relative URI.
prefix	string	The prefix to be used for the name.
attribute	boolean	Declares whether the property definition translates to an attribute instead of an element. Default value is false.
wrapped	boolean	MAY be used only for an array definition. Signifies whether the array is wrapped (for example, <books><book/><book/></books>) or unwrapped (<book/><book/>). Default value is false. The definition takes effect only when defined alongside type being "array" (outside the items).

This object MAY be extended with Specification Extensions.

The namespace field is intended to match the syntax of XML namespaces, although there are a few caveats:

• Version 3.0.3 and earlier of this specification erroneously used the term "absolute URI" instead of "non-relative URI", so authors using namespaces that include a fragment should check tooling support carefully.
• XML allows but discourages relative URI-references, while this specification outright forbids them.
• XML 1.1 allows IRIs (RFC3987) as namespaces, and specifies that namespaces are compared without any encoding or decoding, which means that IRIs encoded to meet this specification's URI syntax requirement cannot be compared to IRIs as-is.

XML Object Examples

Each of the following examples represent the value of the properties keyword in a Schema Object that is omitted for brevity. The JSON and YAML representations of the properties value are followed by an example XML representation produced for the single property shown.

No XML Element

Basic string property:

{
  "animals": {
    "type": "string"
  }
}

animals:
  type: string

<animals>...</animals>

Basic string array property (wrapped is false by default):

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string"
    }
  }
}

animals:
  type: array
  items:
    type: string

<animals>...</animals>
<animals>...</animals>
<animals>...</animals>

XML Name Replacement

{
  "animals": {
    "type": "string",
    "xml": {
      "name": "animal"
    }
  }
}

animals:
  type: string
  xml:
    name: animal

<animal>...</animal>

XML Attribute, Prefix and Namespace

In this example, a full model definition is shown.

{
  "Person": {
    "type": "object",
    "properties": {
      "id": {
        "type": "integer",
        "format": "int32",
        "xml": {
          "attribute": true
        }
      },
      "name": {
        "type": "string",
        "xml": {
          "namespace": "https://example.com/schema/sample",
          "prefix": "sample"
        }
      }
    }
  }
}

Person:
  type: object
  properties:
    id:
      type: integer
      format: int32
      xml:
        attribute: true
    name:
      type: string
      xml:
        namespace: https://example.com/schema/sample
        prefix: sample

<Person id="123">
    <sample:name xmlns:sample="https://example.com/schema/sample">example</sample:name>
</Person>

XML Arrays

Changing the element names:

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string",
      "xml": {
        "name": "animal"
      }
    }
  }
}

animals:
  type: array
  items:
    type: string
    xml:
      name: animal

<animal>value</animal>
<animal>value</animal>

The external name field has no effect on the XML:

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string",
      "xml": {
        "name": "animal"
      }
    },
    "xml": {
      "name": "aliens"
    }
  }
}

animals:
  type: array
  items:
    type: string
    xml:
      name: animal
  xml:
    name: aliens

<animal>value</animal>
<animal>value</animal>

Even when the array is wrapped, if a name is not explicitly defined, the same name will be used both internally and externally:

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string"
    },
    "xml": {
      "wrapped": true
    }
  }
}

animals:
  type: array
  items:
    type: string
  xml:
    wrapped: true

<animals>
  <animals>value</animals>
  <animals>value</animals>
</animals>

To overcome the naming problem in the example above, the following definition can be used:

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string",
      "xml": {
        "name": "animal"
      }
    },
    "xml": {
      "wrapped": true
    }
  }
}

animals:
  type: array
  items:
    type: string
    xml:
      name: animal
  xml:
    wrapped: true

<animals>
  <animal>value</animal>
  <animal>value</animal>
</animals>

Affecting both internal and external names:

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string",
      "xml": {
        "name": "animal"
      }
    },
    "xml": {
      "name": "aliens",
      "wrapped": true
    }
  }
}

animals:
  type: array
  items:
    type: string
    xml:
      name: animal
  xml:
    name: aliens
    wrapped: true

<aliens>
  <animal>value</animal>
  <animal>value</animal>
</aliens>

If we change the external element but not the internal ones:

{
  "animals": {
    "type": "array",
    "items": {
      "type": "string"
    },
    "xml": {
      "name": "aliens",
      "wrapped": true
    }
  }
}

animals:
  type: array
  items:
    type: string
  xml:
    name: aliens
    wrapped: true

<aliens>
  <aliens>value</aliens>
  <aliens>value</aliens>
</aliens>

Security Scheme Object

Defines a security scheme that can be used by the operations.

Supported schemes are HTTP authentication, an API key (either as a header, a cookie parameter, or as a query parameter), OAuth2's common flows (implicit, password, client credentials, and authorization code) as defined in RFC6749, and [[OpenID-Connect-Core]]. Please note that as of 2020, the implicit flow is about to be deprecated by OAuth 2.0 Security Best Current Practice. Recommended for most use cases is Authorization Code Grant flow with PKCE.

Fixed Fields

Field Name	Type	Applies To	Description
type	string	Any	REQUIRED. The type of the security scheme. Valid values are "apiKey", "http", "oauth2", "openIdConnect".
description	string	Any	A description for security scheme. CommonMark syntax MAY be used for rich text representation.
name	string	apiKey	REQUIRED. The name of the header, query or cookie parameter to be used.
in	string	apiKey	REQUIRED. The location of the API key. Valid values are "query", "header", or "cookie".
scheme	string	http	REQUIRED. The name of the HTTP Authentication scheme to be used in the Authorization header as defined in RFC7235. The values used SHOULD be registered in the IANA Authentication Scheme registry. The value is case-insensitive, as defined in RFC7235.
bearerFormat	string	http ("bearer")	A hint to the client to identify how the bearer token is formatted. Bearer tokens are usually generated by an authorization server, so this information is primarily for documentation purposes.
flows	OAuth Flows Object	oauth2	REQUIRED. An object containing configuration information for the flow types supported.
openIdConnectUrl	string	openIdConnect	REQUIRED. Well-known URL to discover the [[OpenID-Connect-Discovery]] provider metadata.

This object MAY be extended with Specification Extensions.

Security Scheme Object Examples

Basic Authentication Example

{
  "type": "http",
  "scheme": "basic"
}

type: http
scheme: basic

API Key Example

{
  "type": "apiKey",
  "name": "api-key",
  "in": "header"
}

type: apiKey
name: api-key
in: header

JWT Bearer Example

{
  "type": "http",
  "scheme": "bearer",
  "bearerFormat": "JWT"
}

type: http
scheme: bearer
bearerFormat: JWT

Implicit OAuth2 Example

{
  "type": "oauth2",
  "flows": {
    "implicit": {
      "authorizationUrl": "https://example.com/api/oauth/dialog",
      "scopes": {
        "write:pets": "modify pets in your account",
        "read:pets": "read your pets"
      }
    }
  }
}

type: oauth2
flows:
  implicit:
    authorizationUrl: https://example.com/api/oauth/dialog
    scopes:
      write:pets: modify pets in your account
      read:pets: read your pets

OAuth Flows Object

Allows configuration of the supported OAuth Flows.

Fixed Fields

Field Name	Type	Description
implicit	OAuth Flow Object	Configuration for the OAuth Implicit flow
password	OAuth Flow Object	Configuration for the OAuth Resource Owner Password flow
clientCredentials	OAuth Flow Object	Configuration for the OAuth Client Credentials flow. Previously called application in OpenAPI 2.0.
authorizationCode	OAuth Flow Object	Configuration for the OAuth Authorization Code flow. Previously called accessCode in OpenAPI 2.0.

This object MAY be extended with Specification Extensions.

OAuth Flow Object

Configuration details for a supported OAuth Flow

Fixed Fields

Field Name	Type	Applies To	Description
authorizationUrl	string	oauth2 ("implicit", "authorizationCode")	REQUIRED. The authorization URL to be used for this flow. This MUST be in the form of a URL. The OAuth2 standard requires the use of TLS.
tokenUrl	string	oauth2 ("password", "clientCredentials", "authorizationCode")	REQUIRED. The token URL to be used for this flow. This MUST be in the form of a URL. The OAuth2 standard requires the use of TLS.
refreshUrl	string	oauth2	The URL to be used for obtaining refresh tokens. This MUST be in the form of a URL. The OAuth2 standard requires the use of TLS.
scopes	Map[string, string]	oauth2	REQUIRED. The available scopes for the OAuth2 security scheme. A map between the scope name and a short description for it. The map MAY be empty.

This object MAY be extended with Specification Extensions.

OAuth Flow Object Example

{
  "type": "oauth2",
  "flows": {
    "implicit": {
      "authorizationUrl": "https://example.com/api/oauth/dialog",
      "scopes": {
        "write:pets": "modify pets in your account",
        "read:pets": "read your pets"
      }
    },
    "authorizationCode": {
      "authorizationUrl": "https://example.com/api/oauth/dialog",
      "tokenUrl": "https://example.com/api/oauth/token",
      "scopes": {
        "write:pets": "modify pets in your account",
        "read:pets": "read your pets"
      }
    }
  }
}

type: oauth2
flows:
  implicit:
    authorizationUrl: https://example.com/api/oauth/dialog
    scopes:
      write:pets: modify pets in your account
      read:pets: read your pets
  authorizationCode:
    authorizationUrl: https://example.com/api/oauth/dialog
    tokenUrl: https://example.com/api/oauth/token
    scopes:
      write:pets: modify pets in your account
      read:pets: read your pets

Security Requirement Object

Lists the required security schemes to execute this operation. The name used for each property MUST correspond to a security scheme declared in the Security Schemes under the Components Object.

A Security Requirement Object MAY refer to multiple security schemes in which case all schemes MUST be satisfied for a request to be authorized. This enables support for scenarios where multiple query parameters or HTTP headers are required to convey security information.

When the security field is defined on the OpenAPI Object or Operation Object and contains multiple Security Requirement Objects, only one of the entries in the list needs to be satisfied to authorize the request. This enables support for scenarios where the API allows multiple, independent security schemes.

An empty Security Requirement Object ({}) indicates anonymous access is supported.

Patterned Fields

Field Pattern	Type	Description
{name}	[string]	Each name MUST correspond to a security scheme which is declared in the Security Schemes under the Components Object. If the security scheme is of type "oauth2" or "openIdConnect", then the value is a list of scope names required for the execution, and the list MAY be empty if authorization does not require a specified scope. For other security scheme types, the array MUST be empty.

Security Requirement Object Examples

See also Appendix F: Resolving Security Requirements in a Referenced Document for an example using Security Requirement Objects in multi-document OpenAPI Descriptions.

Non-OAuth2 Security Requirement

{
  "api_key": []
}

api_key: []

OAuth2 Security Requirement

{
  "petstore_auth": ["write:pets", "read:pets"]
}

petstore_auth:
  - write:pets
  - read:pets

Optional OAuth2 Security

Optional OAuth2 security as would be defined in an OpenAPI Object or an Operation Object:

{
  "security": [
    {},
    {
      "petstore_auth": ["write:pets", "read:pets"]
    }
  ]
}

security:
  - {}
  - petstore_auth:
      - write:pets
      - read:pets

Specification Extensions

While the OpenAPI Specification tries to accommodate most use cases, additional data can be added to extend the specification at certain points.

The extensions properties are implemented as patterned fields that are always prefixed by x-.

Field Pattern	Type	Description
^x-	Any	Allows extensions to the OpenAPI Schema. The field name MUST begin with x-, for example, x-internal-id. The value can be any valid JSON value (null, a primitive, an array, or an object.)

The OpenAPI Initiative maintains several [[OpenAPI-Registry|extension registries]], including registries for individual extension keywords and extension keyword namespaces.

Extensions are one of the best ways to prove the viability of proposed additions to the specification. It is therefore RECOMMENDED that implementations be designed for extensibility to support community experimentation.

Support for any one extension is OPTIONAL, and support for one extension does not imply support for others.

Security Filtering

Some objects in the OpenAPI Specification MAY be declared and remain empty, or be completely removed, even though they are inherently the core of the API documentation.

The reasoning is to allow an additional layer of access control over the documentation. While not part of the specification itself, certain libraries MAY choose to allow access to parts of the documentation based on some form of authentication/authorization.

Two examples of this:

1. The Paths Object MAY be present but empty. It may be counterintuitive, but this may tell the viewer that they got to the right place, but can't access any documentation. They would still have access to at least the Info Object which may contain additional information regarding authentication.
2. The Path Item Object MAY be empty. In this case, the viewer will be aware that the path exists, but will not be able to see any of its operations or parameters. This is different from hiding the path itself from the Paths Object, because the user will be aware of its existence. This allows the documentation provider to finely control what the viewer can see.

Security Considerations

OpenAPI Description Formats

OpenAPI Descriptions use a combination of JSON, YAML, and JSON Schema, and therefore share their security considerations:

• JSON
• YAML
• JSON Schema Core
• JSON Schema Validation

Tooling and Usage Scenarios

In addition, OpenAPI Descriptions are processed by a wide variety of tooling for numerous different purposes, such as client code generation, documentation generation, server side routing, and API testing. OpenAPI Description authors must consider the risks of the scenarios where the OpenAPI Description may be used.

Security Schemes

An OpenAPI Description describes the security schemes used to protect the resources it defines. The security schemes available offer varying degrees of protection. Factors such as the sensitivity of the data and the potential impact of a security breach should guide the selection of security schemes for the API resources. Some security schemes, such as basic auth and OAuth Implicit flow, are supported for compatibility with existing APIs. However, their inclusion in OpenAPI does not constitute an endorsement of their use, particularly for highly sensitive data or operations.

Handling External Resources

OpenAPI Descriptions may contain references to external resources that may be dereferenced automatically by consuming tools. External resources may be hosted on different domains that may be untrusted.

Handling Reference Cycles

References in an OpenAPI Description may cause a cycle. Tooling must detect and handle cycles to prevent resource exhaustion.

Markdown and HTML Sanitization

Certain fields allow the use of Markdown which can contain HTML including script. It is the responsibility of tooling to appropriately sanitize the Markdown.

Appendix A: Revision History

Version	Date	Notes
3.0.4	2024-10-24	Patch release of the OpenAPI Specification 3.0.4
3.0.3	2020-02-20	Patch release of the OpenAPI Specification 3.0.3
3.0.2	2018-10-08	Patch release of the OpenAPI Specification 3.0.2
3.0.1	2017-12-06	Patch release of the OpenAPI Specification 3.0.1
3.0.0	2017-07-26	Release of the OpenAPI Specification 3.0.0
3.0.0-rc2	2017-06-16	rc2 of the 3.0 specification
3.0.0-rc1	2017-04-27	rc1 of the 3.0 specification
3.0.0-rc0	2017-02-28	Implementer's Draft of the 3.0 specification
2.0	2015-12-31	Donation of Swagger 2.0 to the OpenAPI Initiative
2.0	2014-09-08	Release of Swagger 2.0
1.2	2014-03-14	Initial release of the formal document.
1.1	2012-08-22	Release of Swagger 1.1
1.0	2011-08-10	First release of the Swagger Specification

Appendix B: Data Type Conversion

Serializing typed data to plain text, which can occur in text/plain message bodies or multipart parts, as well as in the application/x-www-form-urlencoded format in either URL query strings or message bodies, involves significant implementation- or application-defined behavior.

Schema Objects validate data based on the JSON Schema data model, which only recognizes four primitive data types: strings (which are only broadly interoperable as UTF-8), numbers, booleans, and null. Notably, integers are not a distinct type from other numbers, with type: "integer" being a convenience defined mathematically, rather than based on the presence or absence of a decimal point in any string representation.

The Parameter Object, Header Object, and Encoding Object offer features to control how to arrange values from array or object types. They can also be used to control how strings are further encoded to avoid reserved or illegal characters. However, there is no general-purpose specification for converting schema-validated non-UTF-8 primitive data types (or entire arrays or objects) to strings.

Two cases do offer standards-based guidance:

• RFC3987 provides guidance for converting non-Unicode strings to UTF-8, particularly in the context of URIs (and by extension, the form media types which use the same encoding rules)
• RFC6570 specifies which values, including but not limited to null, are considered undefined and therefore treated specially in the expansion process when serializing based on that specification

Implementations of RFC6570 often have their own conventions for converting non-string values, but these are implementation-specific and not defined by the RFC itself. This is one reason for the OpenAPI Specification to leave these conversions as implementation-defined: It allows using RFC6570 implementations regardless of how they choose to perform the conversions.

To control the serialization of numbers, booleans, and null (or other values RFC6570 deems to be undefined) more precisely, schemas can be defined as type: "string" and constrained using pattern, enum, format, and other keywords to communicate how applications must pre-convert their data prior to schema validation. The resulting strings would not require any further type conversion.

The format keyword can assist in serialization. Some formats (such as date-time) are unambiguous, while others (such as decimal in the Format Registry) are less clear. However, care must be taken with format to ensure that the specific formats are supported by all relevant tools as unrecognized formats are ignored.

Requiring input as pre-formatted, schema-validated strings also improves round-trip interoperability as not all programming languages and environments support the same data types.

Appendix C: Using RFC6570-Based Serialization

Serialization is defined in terms of RFC6570 URI Templates in three scenarios:

Object	Condition
Parameter Object	When schema is present
Header Object	When schema is present
Encoding Object	When encoding for application/x-www-form-urlencoded and any of style, explode, or allowReserved are used

Implementations of this specification MAY use an implementation of RFC6570 to perform variable expansion, however, some caveats apply.

Note that when using style: "form" RFC6570 expansion to produce an application/x-www-form-urlencoded HTTP message body, it is necessary to remove the ? prefix that is produced to satisfy the URI query string syntax.

Note also that not all RFC6570 implementations support all four levels of operators, all of which are needed to fully support the OpenAPI Specification's usage. Using an implementation with a lower level of support will require additional manual construction of URI Templates to work around the limitations.

Equivalences Between Fields and RFC6570 Operators

Certain field values translate to RFC6570 operators (or lack thereof):

field	value	equivalent
style	"simple"	n/a
style	"matrix"	; prefix operator
style	"label"	. prefix operator
style	"form"	? prefix operator
allowReserved	false	n/a
allowReserved	true	+ prefix operator
explode	false	n/a
explode	true	* modifier suffix

Multiple style: "form" parameters are equivalent to a single RFC6570 variable list using the ? prefix operator:

parameters:
- name: foo
  in: query
  schema:
    type: object
  explode: true
- name: bar
  in: query
  schema:
    type: string

This example is equivalent to RFC6570's {?foo*,bar}, and NOT {?foo*}{&bar}. The latter is problematic because if foo is not defined, the result will be an invalid URI. The & prefix operator has no equivalent in the Parameter Object.

Note that RFC6570 does not specify behavior for compound values beyond the single level addressed by explode. The result of using objects or arrays where no behavior is clearly specified for them is implementation-defined.

Delimiters in Parameter Values

Delimiters used by RFC6570 expansion, such as the , used to join arrays or object values with style: "simple", are all automatically percent-encoded as long as allowReserved is false. Note that since RFC6570 does not define a way to parse variables based on a URI Template, users must take care to first split values by delimiter before percent-decoding values that might contain the delimiter character.

When allowReserved is true, both percent-encoding (prior to joining values with a delimiter) and percent-decoding (after splitting on the delimiter) must be done manually at the correct time.

See Appendix E for additional guidance on handling delimiters for style values with no RFC6570 equivalent that already need to be percent-encoded when used as delimiters.

Non-RFC6570 Field Values and Combinations

Configurations with no direct RFC6570 equivalent SHOULD also be handled according to RFC6570. Implementations MAY create a properly delimited URI Template with variables for individual names and values using RFC6570 regular or reserved expansion (based on allowReserved).

This includes:

• the styles pipeDelimited, spaceDelimited, and deepObject, which have no equivalents at all
• the combination of the style form with allowReserved: true, which is not allowed because only one prefix operator can be used at a time
• any parameter name that is not a legal RFC6570 variable name

The Parameter Object's name field has a much more permissive syntax than RFC6570 variable name syntax. A parameter name that includes characters outside of the allowed RFC6570 variable character set MUST be percent-encoded before it can be used in a URI Template.

Examples

Let's say we want to use the following data in a form query string, where formulas is exploded, and words is not:

formulas:
  a: x+y
  b: x/y
  c: x^y
words:
- math
- is
- fun

RFC6570-Equivalent Expansion

This array of Parameter Objects uses regular style: "form" expansion, fully supported by RFC6570:

parameters:
- name: formulas
  in: query
  schema:
    type: object
    additionalProperties:
      type: string
  explode: true
- name: words
  in: query
  schema:
    type: array
    items:
      type: string

This translates to the following URI Template:

{?formulas*,words}

when expanded with the data given earlier, we get:

?a=x%2By&b=x%2Fy&c=x%5Ey&words=math,is,fun

Expansion with Non-RFC6570-Supported Options

But now let's say that (for some reason), we really want that / in the b formula to show up as-is in the query string, and we want our words to be space-separated like in a written phrase. To do that, we'll add allowReserved: true to formulas, and change to style: "spaceDelimited" for words:

parameters:
- name: formulas
  in: query
  schema:
    type: object
    additionalProperties:
      type: string
  explode: true
  allowReserved: true
- name: words
  in: query
  style: spaceDelimited
  explode: false
  schema:
    type: array
    items:
      type: string

We can't combine the ? and + RFC6570 prefixes, and there's no way with RFC6570 to replace the , separator with a space character. So we need to restructure the data to fit a manually constructed URI Template that passes all of the pieces through the right sort of expansion.

Here is one such template, using a made-up convention of words.0 for the first entry in the words value, words.1 for the second, and words.2 for the third:

?a={+a}&b={+b}&c={+c}&words={words.0} {words.1} {words.2}

RFC6570 mentions the use of . "to indicate name hierarchy in substructures," but does not define any specific naming convention or behavior for it. Since the . usage is not automatic, we'll need to construct an appropriate input structure for this new template.

We'll also need to pre-process the values for formulas because while / and most other reserved characters are allowed in the query string by RFC3986, [, ], and # are not, and &, =, and + all have special behavior in the application/x-www-form-urlencoded format, which is what we are using in the query string.

Setting allowReserved: true does not make reserved characters that are not allowed in URIs allowed, it just allows them to be passed through expansion unchanged. Therefore, any tooling still needs to percent-encode those characters because reserved expansion will not do it, but it will leave the percent-encoded triples unchanged. See also Appendix E for further guidance on percent-encoding and form media types, including guidance on handling the delimiter characters for spaceDelimited, pipeDelimited, and deepObject in parameter names and values.

So here is our data structure that arranges the names and values to suit the template above, where values for formulas have []#&=+ pre-percent encoded (although only + appears in this example):

a: x%2By
b: x/y
c: x^y
words.0: math
words.1: is
words.2: fun

Expanding our manually assembled template with our restructured data yields the following query string:

?a=x%2By&b=x/y&c=x%5Ey&words=math%20is%20fun

The / and the pre-percent-encoded %2B have been left alone, but the disallowed ^ character (inside a value) and space characters (in the template but outside of the expanded variables) were percent-encoded.

Undefined Values and Manual URI Template Construction

Care must be taken when manually constructing templates to handle the values that RFC6570 considers to be undefined correctly:

formulas: {}
words:
- hello
- world

Using this data with our original RFC6570-friendly URI Template, {?formulas*,words}, produces the following:

?words=hello,world

This means that the manually constructed URI Template and restructured data need to leave out the formulas object entirely so that the words parameter is the first and only parameter in the query string.

Restructured data:

words.0: hello
words.1: world

Manually constructed URI Template:

?words={words.0} {words.1}

Result:

?words=hello%20world

Illegal Variable Names as Parameter Names

In this example, the heart emoji is not legal in URI Template names (or URIs):

parameters:
- name: ❤️
  in: query
  schema:
    type: string

We can't just pass ❤️: "love!" to an RFC6570 implementation. Instead, we have to pre-percent-encode the name (which is a six-octet UTF-8 sequence) in both the data and the URI Template:

"%E2%9D%A4%EF%B8%8F": love!

{?%E2%9D%A4%EF%B8%8F}

This will expand to the result:

?%E2%9D%A4%EF%B8%8F=love%21

Appendix D: Serializing Headers and Cookies

RFC6570's percent-encoding behavior is not always appropriate for in: "header" and in: "cookie" parameters. In many cases, it is more appropriate to use content with a media type such as text/plain and require the application to assemble the correct string.

For both RFC6265 cookies and HTTP headers using the RFC8941 structured fields syntax, non-ASCII content is handled using base64 encoding (format: "byte"). Note that the standard base64-encoding alphabet includes non-URL-safe characters that are percent-encoded by RFC6570 expansion; serializing values through both encodings is NOT RECOMMENDED.

Most HTTP headers predate the structured field syntax, and a comprehensive assessment of their syntax and encoding rules is well beyond the scope of this specification. While RFC8187 recommends percent-encoding HTTP (header or trailer) field parameters, these parameters appear after a ; character. With style: "simple", that delimiter would itself be percent-encoded, violating the general HTTP field syntax.

Using style: "form" with in: "cookie" is ambiguous for a single value, and incorrect for multiple values. This is true whether the multiple values are the result of using explode: true or not.

This style is specified to be equivalent to RFC6570 form expansion which includes the ? character (see Appendix C for more details), which is not part of the cookie syntax. However, examples of this style in past versions of this specification have not included the ? prefix, suggesting that the comparison is not exact. Because implementations that rely on an RFC6570 implementation and those that perform custom serialization based on the style example will produce different results, it is implementation-defined as to which of the two results is correct.

For multiple values, style: "form" is always incorrect as name=value pairs in cookies are delimited by ; (a semicolon followed by a space character) rather than &.

Appendix E: Percent-Encoding and Form Media Types

NOTE: In this section, the application/x-www-form-urlencoded and multipart/form-data media types are abbreviated as form-urlencoded and form-data, respectively, for readability.

Percent-encoding is used in URIs and media types that derive their syntax from URIs. This process is concerned with three sets of characters, the names of which vary among specifications but are defined as follows for the purposes of this section:

• unreserved characters do not need to be percent-encoded; while it is safe to percent-encode them, doing so produces a URI that is not normalized
• reserved characters either have special behavior in the URI syntax (such as delimiting components) or are reserved for other specifications that need to define special behavior (e.g. form-urlencoded defines special behavior for =, &, and +)
• unsafe characters are known to cause problems when parsing URIs in certain environments

Unless otherwise specified, this section uses RFC3986's definition of reserved and unreserved, and defines the unsafe set as all characters not included in either of those sets.

Percent-Encoding and form-urlencoded

Each URI component (such as the query string) considers some of the reserved characters to be unsafe, either because they serve as delimiters between the components (e.g. #), or (in the case of [ and ]) were historically considered globally unsafe but were later given reserved status for limited purposes.

Reserved characters with no special meaning defined within a component can be left un-percent encoded. However, other specifications can define special meanings, requiring percent-encoding for those characters outside of the additional special meanings.

The form-urlencoded media type defines special meanings for = and & as delimiters, and + as the replacement for the space character (instead of its percent-encoded form of %20). This means that while these three characters are reserved-but-allowed in query strings by RFC3986, they must be percent-encoded in form-urlencoded query strings except when used for their form-urlencoded purposes; see Appendix C for an example of handling + in form values.

Percent-Encoding and form-data

RFC7578 suggests RFC3986-based percent-encoding as a mechanism to keep text-based per-part header data such as file names within the ASCII character set. This suggestion was not part of older (pre-2015) specifications for form-data, so care must be taken to ensure interoperability.

The form-data media type allows arbitrary text or binary data in its parts, so percent-encoding is not needed and is likely to cause interoperability problems unless the Content-Type of the part is defined to require it.

Generating and Validating URIs and form-urlencoded Strings

URI percent encoding and the form-urlencoded media type have complex specification histories spanning multiple revisions and, in some cases, conflicting claims of ownership by different standards bodies. Unfortunately, these specifications each define slightly different percent-encoding rules, which need to be taken into account if the URIs or form-urlencoded message bodies will be subject to strict validation. (Note that many URI parsers do not perform validation by default.)

This specification normatively cites the following relevant standards:

Specification	Date	OAS Usage	Percent-Encoding	Notes
RFC3986	01/2005	URI/URL syntax	[[RFC3986]]	obsoletes [[RFC1738]], [[RFC2396]]
RFC6570	03/2012	style-based serialization	[[RFC3986]]	does not use + for form‑urlencoded
RFC1866	11/1995	content-based serialization	[[RFC1738]]	obsoleted by [[HTML401]] Section 17.13.4.1, [[URL]] Section 5

Style-based serialization is used in the Parameter Object when schema is present, and in the Encoding Object when at least one of style, explode, or allowReserved is present. See Appendix C for more details of RFC6570's two different approaches to percent-encoding, including an example involving +.

Content-based serialization is defined by the Media Type Object, and used with the Parameter Object when the content field is present, and with the Encoding Object based on the contentType field when the fields style, explode, and allowReserved are absent. Each part is encoded based on the media type (e.g. text/plain or application/json), and must then be percent-encoded for use in a form-urlencoded string.

Note that content-based serialization for form-data does not expect or require percent-encoding in the data, only in per-part header values.

Interoperability with Historical Specifications

In most cases, generating query strings in strict compliance with [[RFC3986]] is sufficient to pass validation (including JSON Schema's format: "uri" and format: "uri-reference"), but some form-urlencoded implementations still expect the slightly more restrictive [[RFC1738]] rules to be used.

Since all RFC1738-compliant URIs are compliant with RFC3986, applications needing to ensure historical interoperability SHOULD use RFC1738's rules.

Interoperability with Web Browser Environments

WHATWG is a web browser-oriented standards group that has defined a "URL Living Standard" for parsing and serializing URLs in a browser context, including parsing and serializing form-urlencoded data. WHATWG's percent-encoding rules for query strings are different depending on whether the query string is being treated as form-urlencoded (where it requires more percent-encoding than [[RFC1738]]) or as part of the generic syntax, where it allows characters that [[RFC3986]] forbids.

Implementations needing maximum compatibility with web browsers SHOULD use WHATWG's form-urlencoded percent-encoding rules. However, they SHOULD NOT rely on WHATWG's less stringent generic query string rules, as the resulting URLs would fail RFC3986 validation, including JSON Schema's format: uri and format: uri-reference.

Decoding URIs and form-urlencoded Strings

The percent-decoding algorithm does not care which characters were or were not percent-decoded, which means that URIs percent-encoded according to any specification will be decoded correctly.

Similarly, all form-urlencoded decoding algorithms simply add +-for-space handling to the percent-decoding algorithm, and will work regardless of the encoding specification used.

However, care must be taken to use form-urlencoded decoding if + represents a space, and to use regular percent-decoding if + represents itself as a literal value.

Percent-Encoding and Illegal or Reserved Delimiters

The [, ], |, and space characters, which are used as delimiters for the deepObject, pipeDelimited, and spaceDelimited styles, respectively, all MUST be percent-encoded to comply with [[RFC3986]]. This requires users to pre-encode the character(s) in some other way in parameter names and values to distinguish them from the delimiter usage when using one of these styles.

The space character is always illegal and encoded in some way by all implementations of all versions of the relevant standards. While one could use the form-urlencoded convention of + to distinguish spaces in parameter names and values from spaceDelimited delimiters encoded as %20, the specifications define the decoding as a single pass, making it impossible to distinguish the different usages in the decoded result.

Some environments use [, ], and possibly | unencoded in query strings without apparent difficulties, and WHATWG's generic query string rules do not require percent-encoding them. Code that relies on leaving these delimiters unencoded, while using regular percent-encoding for them within names and values, is not guaranteed to be interoperable across all implementations.

For maximum interoperability, it is RECOMMENDED to either define and document an additional escape convention while percent-encoding the delimiters for these styles, or to avoid these styles entirely. The exact method of additional encoding/escaping is left to the API designer, and is expected to be performed before serialization and encoding described in this specification, and reversed after this specification's encoding and serialization steps are reversed. This keeps it outside of the processes governed by this specification.

Appendix F: Resolving Security Requirements in a Referenced Document

This appendix shows how to retrieve an HTTP-accessible multi-document OpenAPI Description (OAD) and resolve a Security Requirement Object in the referenced (non-entry) document. See Resolving Implicit Connections for more information.

First, the entry document is where parsing begins. It defines the MySecurity security scheme to be JWT-based, and it defines a Path Item as a reference to a component in another document:

GET /api/description/openapi HTTP/1.1
Host: www.example.com
Accept: application/openapi+json

"components": {
  "securitySchemes": {
    "MySecurity": {
      "type": "http",
      "scheme": "bearer",
      "bearerFormat": "JWT"
    }
  }
},
"paths": {
  "/foo": {
    "$ref": "other#/components/pathItems/Foo"
  }
}

GET /api/description/openapi HTTP/1.1
Host: www.example.com
Accept: application/openapi+yaml

components:
  securitySchemes:
    MySecurity:
      type: http
      scheme: bearer
      bearerFormat: JWT
paths:
  /foo:
    $ref: 'other#/components/pathItems/Foo'

This entry document references another document, other, without using a file extension. This gives the client the flexibility to choose an acceptable format on a resource-by-resource basis, assuming both representations are available:

GET /api/description/other HTTP/1.1
Host: www.example.com
Accept: application/openapi+json

"components": {
  "securitySchemes": {
    "MySecurity": {
      "type": "http",
      "scheme": "basic"
    }
  },
  "pathItems": {
    "Foo": {
      "get": {
        "security": [
          "MySecurity": []
        ]
      }
    }
  }
}

GET /api/description/other HTTP/1.1
Host: www.example.com
Accept: application/openapi+yaml

components:
  securitySchemes:
    MySecurity:
      type: http
      scheme: basic
  pathItems:
    Foo:
      get:
        security:
          - MySecurity: []

In the other document, the referenced path item has a Security Requirement for a Security Scheme, MySecurity. The same Security Scheme exists in the original entry document. As outlined in Resolving Implicit Connections, MySecurity is resolved with an implementation-defined behavior. However, documented in that section, it is RECOMMENDED that tools resolve component names from the entry document. As with all implementation-defined behavior, it is important to check tool documentation to determine which behavior is supported.