diff --git a/index.d.ts b/index.d.ts
new file mode 100644
index 0000000..9b321db
--- /dev/null
+++ b/index.d.ts
@@ -0,0 +1,428 @@
+declare module "flexsearch" {
+    // Type definitions for flexsearch 0.7
+    // Project: https://github.com/nextapps-de/flexsearch/
+    // Definitions by: LOSSES Don <https://github.com/Losses>
+    // Definitions: https://github.com/DefinitelyTyped/DefinitelyTyped
+
+    /************************************/
+    /* Utils                            */
+    /************************************/
+    export type Id = number | string;
+    export type Limit = number;
+    export type ExportHandler<T> = (id: string | number, value: T) => void;
+    export type AsyncCallback<T = undefined> = T extends undefined
+        ? () => void
+        : (result: T) => void;
+    export type UnknownFunction = (...x: unknown[]) => unknown;
+
+    export type StoreOption = boolean | string | string[];
+    export type EnrichStoreOption = true | string | string[];
+
+    /************************************/
+    /* Common Options                   */
+    /************************************/
+
+    /**
+     * **Document:**
+     * * Presets: https://github.com/nextapps-de/flexsearch#presets
+     */
+    export type Preset = "memory" | "performance" | "match" | "score" | "default";
+
+    /**
+     * **Document:**
+     * * Tokenizer: https://github.com/nextapps-de/flexsearch#tokenizer-prefix-search
+     * * Add custom tokenizer: https://github.com/nextapps-de/flexsearch#add-custom-tokenizer
+     */
+    export type Tokenizer =
+        | "strict"
+        | "forward"
+        | "reverse"
+        | "full"
+        | ((x: string) => string[]);
+
+    /**
+     * **Document:**
+     * * Encoders: https://github.com/nextapps-de/flexsearch#encoders
+     */
+    export type Encoders =
+        | false
+        | "default"
+        | "simple"
+        | "balance"
+        | "advanced"
+        | "extra"
+        | ((x: string) => string[]);
+
+    /**
+     * **Document:**
+     * * Contextual search: https://github.com/nextapps-de/flexsearch#contextual
+     */
+    export interface ContextOptions {
+        resolution: number;
+        depth: false | number;
+        bidirectional: boolean;
+    }
+
+    /**
+     * **Document:**
+     * * Search options: https://github.com/nextapps-de/flexsearch#search-options
+     */
+    export interface SearchOptions {
+        query?: string;
+        limit?: number;
+        offset?: number;
+        suggest?: boolean;
+    }
+
+    /**
+     * **Document:**
+     * * The document descriptor: https://github.com/nextapps-de/flexsearch#the-document-descriptor
+     */
+    export interface Descriptor<T, Store extends StoreOption = false> {
+        id: string | number;
+        field: string[] | Array<IndexOptions<T, Store>>;
+    }
+
+    /**
+     * **Document:**
+     * * Context Options: https://github.com/nextapps-de/flexsearch#context-options
+     */
+    export interface ContextOptions {
+        resolution: number;
+        depth: false | number;
+        bidirectional: boolean;
+    }
+
+    /**
+     * **Document:**
+     * * Charset options: https://github.com/nextapps-de/flexsearch#charset-options
+     */
+    export interface CharsetOptions {
+        split: false | string | RegExp;
+        rtl: boolean;
+        encode: (x: string) => string[];
+    }
+
+    export interface Stemmer {
+        [key: string]: string;
+    }
+
+    export interface Matcher {
+        [key: string]: string;
+    }
+
+    export type FilterFunction = (x: string) => boolean;
+    export type FilterArray = string[];
+
+    /**
+     * **Document:**
+     * * Language Options: https://github.com/nextapps-de/flexsearch#language-options
+     * * Language: https://github.com/nextapps-de/flexsearch#languages
+     */
+    export interface LanguageOptions {
+        stemmer: false | string | Stemmer | UnknownFunction;
+        filter: false | string | FilterArray | FilterFunction;
+        matcher: false | string | Matcher | UnknownFunction;
+    }
+
+    /**
+     * These options will determine how the documents be indexed.
+     *
+     * **Generic type parameters:**
+     *
+     * @template T The type of the document.
+     * @template Store If store is enabled.
+     *
+     * **Document:**
+     * * Index options: https://github.com/nextapps-de/flexsearch#index-options
+     * * Language: https://github.com/nextapps-de/flexsearch#languages
+     */
+    export interface IndexOptions<T, Store extends StoreOption = false> {
+        preset?: Preset;
+        tokenize?: Tokenizer;
+        cache?: boolean | number;
+        resolution?: number;
+        context?: boolean | IndexOptions<T, Store> | ContextOptions;
+        optimize?: boolean;
+        boost?: (words: string[], term: string, index: number) => number;
+
+        // Language-specific Options and Encoding
+        charset?: CharsetOptions | string;
+        language?: LanguageOptions | string;
+        encode?: Encoders;
+        stemmer?: LanguageOptions["stemmer"];
+        filter?: LanguageOptions["filter"];
+        matcher?: LanguageOptions["matcher"];
+    }
+
+    /************************************/
+    /* Index Search                     */
+    /************************************/
+
+    export type IndexSearchResult = Id[];
+
+    /**
+     * **Document:**
+     * * Basic usage and variants: https://github.com/nextapps-de/flexsearch#basic-usage-and-variants
+     * * API overview: https://github.com/nextapps-de/flexsearch#api-overview
+     * * Usage: https://github.com/nextapps-de/flexsearch#usage
+     */
+
+    export class Index {
+        constructor(x?: Preset | IndexOptions<string>);
+        add(id: Id, item: string): this;
+        append(id: Id, item: string): this;
+        update(id: Id, item: string): this;
+        remove(target: Id): this;
+        search(query: string, options?: Limit | SearchOptions): IndexSearchResult;
+        search(
+            query: string,
+            limit: number,
+            options: SearchOptions
+        ): IndexSearchResult;
+        search(options: SearchOptions): IndexSearchResult;
+
+        // https://github.com/nextapps-de/flexsearch#check-existence-of-already-indexed-ids
+        contain(id: Id): boolean;
+
+        export(handler: ExportHandler<string>): Promise<void>;
+        import(id: Id, item: string): Promise<void>;
+
+        // Async Methods
+        addAsync(
+            id: Id,
+            item: string,
+            callback?: AsyncCallback<this>
+        ): Promise<this>;
+        appendAsync(
+            id: Id,
+            item: string,
+            callback?: AsyncCallback<this>
+        ): Promise<this>;
+        updateAsync(
+            id: Id,
+            item: string,
+            callback?: AsyncCallback<this>
+        ): Promise<this>;
+        removeAsync(target: Id, callback?: AsyncCallback<this>): Promise<this>;
+        searchAsync(
+            query: string,
+            options?: Limit | SearchOptions,
+            callback?: AsyncCallback<IndexSearchResult>
+        ): Promise<IndexSearchResult>;
+        searchAsync(
+            query: string,
+            limit: number,
+            options?: Limit | SearchOptions
+        ): IndexSearchResult;
+        searchAsync(options: SearchOptions): Promise<IndexSearchResult>;
+    }
+
+    /**
+     * **Document:**
+     * * Basic usage and variants: https://github.com/nextapps-de/flexsearch#basic-usage-and-variants
+     * * API overview: https://github.com/nextapps-de/flexsearch#api-overview
+     * * Worker index: https://github.com/nextapps-de/flexsearch#worker-index
+     */
+    export class Worker {
+        constructor(x?: Preset | IndexOptions<string>);
+
+        add(id: Id, item: string, callback?: AsyncCallback<Worker>): Promise<this>;
+        append(id: Id, item: string, callback?: AsyncCallback<this>): Promise<this>;
+        update(id: Id, item: string, callback?: AsyncCallback<this>): Promise<this>;
+        remove(target: Id, callback?: AsyncCallback<this>): Promise<this>;
+        search(
+            query: string,
+            options?: Limit | SearchOptions,
+            callback?: AsyncCallback<IndexSearchResult>
+        ): Promise<IndexSearchResult>;
+        search(
+            query: string,
+            limit: number,
+            options?: Limit | SearchOptions
+        ): IndexSearchResult;
+        search(options: SearchOptions): Promise<IndexSearchResult>;
+
+        // Async Methods
+        addAsync(
+            id: Id,
+            item: string,
+            callback?: AsyncCallback<this>
+        ): Promise<this>;
+        appendAsync(
+            id: Id,
+            item: string,
+            callback?: AsyncCallback<this>
+        ): Promise<this>;
+        updateAsync(
+            id: Id,
+            item: string,
+            callback?: AsyncCallback<this>
+        ): Promise<this>;
+        removeAsync(target: Id, callback?: AsyncCallback<this>): Promise<this>;
+        searchAsync(
+            query: string,
+            options?: Limit | SearchOptions,
+            callback?: AsyncCallback<IndexSearchResult>
+        ): Promise<IndexSearchResult>;
+        searchAsync(
+            query: string,
+            limit: number,
+            options?: Limit | SearchOptions
+        ): IndexSearchResult;
+        searchAsync(options: SearchOptions): Promise<IndexSearchResult>;
+    }
+
+    /************************************/
+    /* Document Search                  */
+    /************************************/
+
+    /*
+     * **Document:**
+     * * Document options: https://github.com/nextapps-de/flexsearch#document-options
+     */
+    export interface DocumentOptions<T, Store extends StoreOption = false> {
+        id: string;
+        tag?: false | string;
+        index:
+            | string
+            | string[]
+            | Array<IndexOptions<T, Store> & { field: string }>;
+        store?: Store;
+    }
+
+    /*
+     * **Document:**
+     * * Index options: https://github.com/nextapps-de/flexsearch#index-options
+     */
+    export interface IndexOptionsForDocumentSearch<
+        T,
+        Store extends StoreOption = false
+    > extends IndexOptions<T, Store> {
+        // Additional Options for Document Indexes
+        worker?: boolean;
+        document?: DocumentOptions<T, Store> | Descriptor<T, Store>;
+    }
+
+    export interface SimpleDocumentSearchResultSetUnit {
+        field: string;
+        result: Id[];
+    }
+
+    export interface EnrichedDocumentSearchResultSetUnitResultUnit<T> {
+        id: Id[];
+        doc: T;
+    }
+
+    export interface EnrichedDocumentSearchResultSetUnit<T> {
+        field: string;
+        result: Array<EnrichedDocumentSearchResultSetUnitResultUnit<T>>;
+    }
+
+    /**
+     *  # Document Search Result
+     *
+     *  To make your result return the full document:
+     *  * set `store` to `true` while creating the document;
+     *  * set `enrich` to `true` while searching.
+     *
+     *  If neither of these conditions is met, then the returned result will be a `ISimpleDocumentSearchResult`.
+     */
+    export type DocumentSearchResult<
+        T,
+        Store extends StoreOption = false,
+        Enrich extends boolean = false
+    > = [Store, Enrich] extends [EnrichStoreOption, true]
+        ? Array<EnrichedDocumentSearchResultSetUnit<T>>
+        : SimpleDocumentSearchResultSetUnit[];
+
+    /**
+     * **Document:**
+     * * Document search options: https://github.com/nextapps-de/flexsearch#document-search-options
+     */
+    export interface DocumentSearchOptions<T extends boolean> extends SearchOptions {
+        index?: string | string[] | SearchOptions[];
+        tag?: string | string[];
+        enrich?: T;
+        bool?: "and" | "or";
+    }
+
+    /**
+     * **Document:**
+     * * Basic usage and variants: https://github.com/nextapps-de/flexsearch#basic-usage-and-variants
+     * * API overview: https://github.com/nextapps-de/flexsearch#api-overview
+     * * Document store: https://github.com/nextapps-de/flexsearch#document-store
+     */
+    export class Document<T, Store extends StoreOption = false> {
+        constructor(
+            options: IndexOptionsForDocumentSearch<T, Store>,
+            typeHack?: T
+        );
+        add(document: T): this;
+        add(id: Id, document: T): this;
+        append(document: T): this;
+        append(id: Id, document: T): this;
+        update(document: T): this;
+        update(id: Id, document: T): this;
+        remove(target: Id | T): this;
+        search(query: string, limit?: number): SimpleDocumentSearchResultSetUnit[];
+
+        // https://github.com/nextapps-de/flexsearch#field-search
+        search(
+            query: string,
+            options: string[] | Partial<DocumentSearchOptions<boolean>>
+        ): SimpleDocumentSearchResultSetUnit[];
+
+        search<Enrich extends boolean = false>(
+            query: string,
+            limit?: number,
+            options?: Partial<DocumentSearchOptions<Enrich>>
+        ): DocumentSearchResult<T, Store, Enrich>;
+        search(
+            options: Partial<DocumentSearchOptions<boolean>>
+        ): SimpleDocumentSearchResultSetUnit[];
+        export(handler: ExportHandler<T>): Promise<void>;
+        import(id: Id, document: T): Promise<void>;
+
+        // Async Methods
+        addAsync(id: Id, document: T, callback?: AsyncCallback): Promise<this>;
+        appendAsync(id: Id, document: T, callback?: AsyncCallback): Promise<this>;
+        updateAsync(id: Id, document: T, callback?: AsyncCallback): Promise<this>;
+        removeAsync(target: Id | T, callback?: AsyncCallback): Promise<this>;
+        searchAsync<Enrich extends boolean = false>(
+            query: string,
+            options: string[] | Partial<DocumentSearchOptions<Enrich>>
+        ): Promise<DocumentSearchResult<T, Store, Enrich>>;
+        searchAsync(
+            query: string,
+            limit?: number
+        ): Promise<SimpleDocumentSearchResultSetUnit[]>;
+        searchAsync(
+            query: string,
+            limit: number,
+            callback: AsyncCallback<SimpleDocumentSearchResultSetUnit[]>
+        ): Promise<this>;
+        searchAsync<Enrich extends boolean = false>(
+            query: string,
+            options: Partial<DocumentSearchOptions<Enrich>>,
+            callback: AsyncCallback<DocumentSearchResult<T, Store, Enrich>>
+        ): Promise<this>;
+        searchAsync<Enrich extends boolean = false>(
+            options: Partial<DocumentSearchOptions<Enrich>>
+        ): Promise<DocumentSearchResult<T, Store, Enrich>>;
+        searchAsync<Enrich extends boolean = false>(
+            options: Partial<DocumentSearchOptions<Enrich>>,
+            callback: AsyncCallback<DocumentSearchResult<T, Store, Enrich>>
+        ): Promise<this>;
+    }
+
+    /************************************/
+    /* Miscellaneous                    */
+    /************************************/
+    export function create(options: IndexOptions<string>): Index;
+    export function registerCharset(name: string, charset: CharsetOptions): void;
+    export function registerLanguage(
+        name: string,
+        language: LanguageOptions
+    ): void;
+}
\ No newline at end of file
diff --git a/package.json b/package.json
index 850050b..6f804c1 100644
--- a/package.json
+++ b/package.json
@@ -61,6 +61,7 @@
     "dist/**",
     "src/**",
     "task/**",
+    "index.d.ts",
     "README.md",
     "CHANGELOG.md",
     "LICENSE"