diff --git a/.github/workflows/test-application.yaml b/.github/workflows/test-application.yaml
index 93d54dcc..39bfaaf8 100644
--- a/.github/workflows/test-application.yaml
+++ b/.github/workflows/test-application.yaml
@@ -8,8 +8,72 @@ on:
             - '[0-9]+.x'
 
 jobs:
-    php:
-        name: 'Run tests with php ${{ matrix.php-version }} with symfony ${{ matrix.symfony-version}}'
+    code-style:
+      runs-on: ubuntu-latest
+
+      steps:
+        - name: Checkout project
+          uses: actions/checkout@v3
+
+        - name: Install and configure PHP
+          uses: shivammathur/setup-php@v2
+          with:
+            coverage: none
+            php-version: 8.1
+
+        - name: Get composer cache directory
+          id: composer-cache-dir
+          run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+        - name: Cache dependencies
+          uses: actions/cache@v2
+          id: composer-cache
+          with:
+            path: ${{ steps.composer-cache-dir.outputs.dir }}
+            key: ${{ runner.os }}-composer-${{ hashFiles('composer.lock') }}
+            restore-keys: |
+              ${{ runner.os }}-composer-
+
+        - name: Install dependencies
+          run: composer install --no-interaction --prefer-dist
+
+        - name: Fix code style
+          run: vendor/bin/phpcs -p --standard=PSR2 --ignore=vendor/ ./
+
+    phpstan:
+      runs-on: ubuntu-latest
+
+      steps:
+        - name: Checkout project
+          uses: actions/checkout@v3
+
+        - name: Install and configure PHP
+          uses: shivammathur/setup-php@v2
+          with:
+            coverage: none
+            php-version: 8.1
+
+        - name: Get composer cache directory
+          id: composer-cache-dir
+          run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+        - name: Cache dependencies
+          uses: actions/cache@v2
+          id: composer-cache
+          with:
+            path: ${{ steps.composer-cache-dir.outputs.dir }}
+            key: ${{ runner.os }}-composer-${{ hashFiles('composer.lock') }}
+            restore-keys: |
+              ${{ runner.os }}-composer-
+
+        - name: Install dependencies
+          run: composer install --no-interaction --prefer-dist
+
+        - name: Fix code style
+          run: vendor/bin/phpstan analyse -l3 src/
+
+    unit-test:
+        name: 'Run unit tests with php ${{ matrix.php-version }} with symfony ${{ matrix.symfony-version}}'
         runs-on: ubuntu-latest
 
         strategy:
@@ -17,19 +81,15 @@ jobs:
             matrix:
                 include:
                     - php-version: '8.0'
-                      lint: true
                       symfony-version: '5.4.*'
 
                     - php-version: '8.1'
-                      lint: false
                       symfony-version: '5.4.*'
 
                     - php-version: '8.1'
-                      lint: false
                       symfony-version: '6.0.*'
 
                     - php-version: '8.1'
-                      lint: false
                       symfony-version: '6.1.*'
 
         steps:
@@ -61,14 +121,51 @@ jobs:
                   composer require --no-update symfony/serializer:${{ matrix.symfony-version }}
                   composer install --no-interaction --prefer-dist
 
-            - name: Fix code style
-              if: ${{ matrix.lint }}
-              run: vendor/bin/phpcs -p --standard=PSR2 --ignore=vendor/ ./
-
             - name: Setup OpenSearch
               uses: ankane/setup-opensearch@v1
               with:
                 opensearch-version: '1.2'
 
             - name: Run tests
-              run: vendor/bin/phpunit --coverage-clover=coverage.xml
+              run: vendor/bin/phpunit --testsuite=unit --coverage-clover=coverage.xml
+
+    functional-test:
+      name: 'Run functional tests'
+      runs-on: ubuntu-latest
+
+      steps:
+        - name: Checkout project
+          uses: actions/checkout@v3
+
+        - name: Install and configure PHP
+          uses: shivammathur/setup-php@v2
+          with:
+            coverage: none
+            php-version: 8.1
+
+        - name: Get composer cache directory
+          id: composer-cache-dir
+          run: echo "::set-output name=dir::$(composer config cache-files-dir)"
+
+        - name: Cache dependencies
+          uses: actions/cache@v2
+          id: composer-cache
+          with:
+            path: ${{ steps.composer-cache-dir.outputs.dir }}
+            key: ${{ runner.os }}-composer-${{ hashFiles('composer.lock') }}
+            restore-keys: |
+              ${{ runner.os }}-composer-
+
+        - name: Install dependencies
+          run: |
+            composer validate --strict
+            composer require --no-update symfony/serializer:${{ matrix.symfony-version }}
+            composer install --no-interaction --prefer-dist
+
+        - name: Setup OpenSearch
+          uses: ankane/setup-opensearch@v1
+          with:
+            opensearch-version: '1.2'
+
+        - name: Run tests
+          run: vendor/bin/phpunit --testsuite=functional
\ No newline at end of file
diff --git a/composer.json b/composer.json
index 9e6ccf54..ccb3d4c9 100644
--- a/composer.json
+++ b/composer.json
@@ -25,7 +25,8 @@
     },
     "require-dev": {
         "phpunit/phpunit": "^9.5",
-        "squizlabs/php_codesniffer": "^3.0"
+        "squizlabs/php_codesniffer": "^3.0",
+        "phpstan/phpstan": "^1.8"
     },
     "autoload": {
         "psr-4": {
diff --git a/src/Aggregation/AbstractAggregation.php b/src/Aggregation/AbstractAggregation.php
index 99a1e8ce..6f5fc041 100644
--- a/src/Aggregation/AbstractAggregation.php
+++ b/src/Aggregation/AbstractAggregation.php
@@ -12,6 +12,7 @@
 namespace OpenSearchDSL\Aggregation;
 
 use OpenSearchDSL\BuilderBag;
+use OpenSearchDSL\BuilderInterface;
 use OpenSearchDSL\NameAwareTrait;
 use OpenSearchDSL\NamedBuilderInterface;
 use OpenSearchDSL\ParametersTrait;
@@ -63,7 +64,7 @@ public function addAggregation(AbstractAggregation $abstractAggregation): static
     /**
      * Returns all sub aggregations.
      *
-     * @return BuilderBag[]|NamedBuilderInterface[]
+     * @return BuilderInterface[]
      */
     public function getAggregations(): array
     {
@@ -76,11 +77,8 @@ public function getAggregations(): array
 
     /**
      * Returns sub aggregation.
-     * @param string $name Aggregation name to return.
-     *
-     * @return AbstractAggregation|NamedBuilderInterface|null
      */
-    public function getAggregation($name)
+    public function getAggregation(string $name): ?BuilderInterface
     {
         if ($this->aggregations && $this->aggregations->has($name)) {
             return $this->aggregations->get($name);
@@ -112,7 +110,7 @@ public function toArray(): array
      *
      * @return array
      */
-    protected function collectNestedAggregations()
+    protected function collectNestedAggregations(): array
     {
         $result = [];
         /** @var AbstractAggregation $aggregation */
diff --git a/src/Aggregation/Metric/TopHitsAggregation.php b/src/Aggregation/Metric/TopHitsAggregation.php
index 907a90f8..4c016ac8 100644
--- a/src/Aggregation/Metric/TopHitsAggregation.php
+++ b/src/Aggregation/Metric/TopHitsAggregation.php
@@ -23,18 +23,17 @@
  */
 class TopHitsAggregation extends AbstractAggregation
 {
-    public BuilderInterface $sort;
     use MetricTrait;
 
     /**
-     * @var int Number of top matching hits to return per bucket.
+     * @var int|null Number of top matching hits to return per bucket.
      */
-    private int $size;
+    private ?int $size;
 
     /**
-     * @var int The offset from the first result you want to fetch.
+     * @var int|null The offset from the first result you want to fetch.
      */
-    private int $from;
+    private ?int $from;
 
     /**
      * @var BuilderInterface[] How the top matching hits should be sorted.
@@ -42,14 +41,12 @@ class TopHitsAggregation extends AbstractAggregation
     private array $sorts = [];
 
     /**
-     * Constructor for top hits.
-     *
      * @param string                $name Aggregation name.
      * @param null|int              $size Number of top matching hits to return per bucket.
      * @param null|int              $from The offset from the first result you want to fetch.
      * @param null|BuilderInterface $sort How the top matching hits should be sorted.
      */
-    public function __construct($name, $size = null, $from = null, $sort = null)
+    public function __construct(string $name, ?int $size = null, ?int $from = null, ?BuilderInterface $sort = null)
     {
         parent::__construct($name);
         $this->setFrom($from);
@@ -57,22 +54,12 @@ public function __construct($name, $size = null, $from = null, $sort = null)
         $this->addSort($sort);
     }
 
-    /**
-     * Return from.
-     *
-     * @return int
-     */
-    public function getFrom()
+    public function getFrom(): ?int
     {
         return $this->from;
     }
 
-    /**
-     * @param int $from
-     *
-     * @return $this
-     */
-    public function setFrom($from)
+    public function setFrom(?int $from): self
     {
         $this->from = $from;
 
@@ -82,51 +69,36 @@ public function setFrom($from)
     /**
      * @return BuilderInterface[]
      */
-    public function getSorts()
+    public function getSorts(): array
     {
         return $this->sorts;
     }
 
     /**
      * @param BuilderInterface[] $sorts
-     *
-     * @return $this
      */
-    public function setSorts(array $sorts)
+    public function setSorts(array $sorts): self
     {
         $this->sorts = $sorts;
 
         return $this;
     }
 
-    /**
-     * Add sort.
-     *
-     * @param BuilderInterface $sort
-     */
-    public function addSort($sort)
+    public function addSort(BuilderInterface $sort): self
     {
         $this->sorts[] = $sort;
+
+        return $this;
     }
 
-    /**
-     * @param int $size
-     *
-     * @return $this
-     */
-    public function setSize($size)
+    public function setSize(?int $size): self
     {
         $this->size = $size;
 
         return $this;
     }
 
-    /**
-     * Return size.
-     *
-     * @return int
-     */
-    public function getSize()
+    public function getSize(): ?int
     {
         return $this->size;
     }
@@ -139,10 +111,7 @@ public function getType(): string
         return 'top_hits';
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getArray(): array
+    public function getArray(): array|stdClass
     {
         $sortsOutput = [];
         $addedSorts = array_filter($this->getSorts());
@@ -154,43 +123,12 @@ public function getArray(): array
             $sortsOutput = null;
         }
 
-        $output = array_filter(
-            [
-                'sort' => $sortsOutput,
-                'size' => $this->getSize(),
-                'from' => $this->getFrom(),
-            ],
-            fn($val) => $val || is_array($val) || ($val || is_numeric($val))
-        );
+        $output = array_filter([
+            'sort' => $sortsOutput,
+            'size' => $this->getSize(),
+            'from' => $this->getFrom(),
+        ]);
 
         return empty($output) ? new stdClass() : $output;
     }
-
-    /**
-     * @deprecated sorts now is a container, use `getSorts()`instead.
-     * Return sort.
-     *
-     * @return BuilderInterface
-     */
-    public function getSort()
-    {
-        if (isset($this->sorts[0])) {
-            return $this->sorts[0];
-        }
-
-        return null;
-    }
-
-    /**
-     * @deprecated sorts now is a container, use `addSort()`instead.
-     *
-     *
-     * @return $this
-     */
-    public function setSort(BuilderInterface $sort)
-    {
-        $this->sort = $sort;
-
-        return $this;
-    }
 }
diff --git a/src/ParametersTrait.php b/src/ParametersTrait.php
index 9040e8a7..48a54f75 100644
--- a/src/ParametersTrait.php
+++ b/src/ParametersTrait.php
@@ -18,6 +18,9 @@
  */
 trait ParametersTrait
 {
+    /**
+     * @var array<string, array|string|int|float|bool|stdClass>
+     */
     private array $parameters = [];
 
     public function hasParameter(string $name): bool
@@ -39,6 +42,9 @@ public function getParameter(string $name): array|string|int|float|bool|stdClass
         return $this->parameters[$name];
     }
 
+    /**
+     * @return array<string, array|string|int|float|bool|stdClass>
+     */
     public function getParameters(): array
     {
         return $this->parameters;
diff --git a/src/Query/Compound/BoolQuery.php b/src/Query/Compound/BoolQuery.php
index 1203882d..8362ff0e 100644
--- a/src/Query/Compound/BoolQuery.php
+++ b/src/Query/Compound/BoolQuery.php
@@ -30,12 +30,15 @@ class BoolQuery implements BuilderInterface
     public const SHOULD = 'should';
     public const FILTER = 'filter';
 
+    /**
+     * @var array<string, array<string, BuilderInterface>>
+     */
     private array $container = [];
 
     /**
      * Constructor to prepare container.
      *
-     * @param array $container
+     * @param array<string, BuilderInterface|BuilderInterface[]> $container
      */
     public function __construct(array $container = [])
     {
@@ -51,11 +54,9 @@ public function __construct(array $container = [])
     /**
      * Returns the query instances (by bool type).
      *
-     * @param  string|null $boolType
-     *
-     * @return array
+     * @return array<string, BuilderInterface>
      */
-    public function getQueries($boolType = null)
+    public function getQueries(?string $boolType = null): array
     {
         if ($boolType === null) {
             $queries = [];
@@ -79,19 +80,19 @@ public function getQueries($boolType = null)
      *
      * @param BuilderInterface $query Query add to the bool.
      * @param string           $type  Bool type. Example: must, must_not, should.
-     * @param string           $key   Key that indicates a builder id.
+     * @param string|null      $key   Key that indicates a builder id.
      *
      * @return string Key of added builder.
      *
      * @throws UnexpectedValueException
      */
-    public function add(BuilderInterface $query, $type = self::MUST, $key = null)
+    public function add(BuilderInterface $query, string $type = self::MUST, ?string $key = null): string
     {
         if (!in_array($type, [self::MUST, self::MUST_NOT, self::SHOULD, self::FILTER])) {
             throw new UnexpectedValueException(sprintf('The bool operator %s is not supported', $type));
         }
 
-        if (!$key) {
+        if ($key === null) {
             $key = bin2hex(random_bytes(30));
         }
 
@@ -115,7 +116,6 @@ public function toArray(): array
         $output = [];
 
         foreach ($this->container as $boolType => $builders) {
-            /** @var BuilderInterface $builder */
             foreach ($builders as $builder) {
                 $output[$boolType][] = $builder->toArray();
             }
@@ -130,9 +130,6 @@ public function toArray(): array
         return [$this->getType() => $output];
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function getType(): string
     {
         return 'bool';
diff --git a/src/Query/Span/SpanContainingQuery.php b/src/Query/Span/SpanContainingQuery.php
index 162fa07c..1b806ba6 100644
--- a/src/Query/Span/SpanContainingQuery.php
+++ b/src/Query/Span/SpanContainingQuery.php
@@ -22,62 +22,22 @@ class SpanContainingQuery implements SpanQueryInterface
 {
     use ParametersTrait;
 
-    /**
-     * @param SpanQueryInterface
-     */
-    private $little;
-
-    /**
-     * @param SpanQueryInterface
-     */
-    private $big;
-
-    /**
-     * @param SpanQueryInterface $little
-     * @param SpanQueryInterface $big
-     */
-    public function __construct(SpanQueryInterface $little, SpanQueryInterface $big)
-    {
-        $this->setLittle($little);
-        $this->setBig($big);
+    public function __construct(
+        private SpanQueryInterface $little,
+        private SpanQueryInterface $big
+    ) {
     }
 
-    /**
-     * @return SpanQueryInterface
-     */
-    public function getLittle()
+    public function getLittle(): SpanQueryInterface
     {
         return $this->little;
     }
 
-    /**
-     * @return $this
-     */
-    public function setLittle(SpanQueryInterface $little)
-    {
-        $this->little = $little;
-
-        return $this;
-    }
-
-    /**
-     * @return SpanQueryInterface
-     */
-    public function getBig()
+    public function getBig(): SpanQueryInterface
     {
         return $this->big;
     }
 
-    /**
-     * @return $this
-     */
-    public function setBig(SpanQueryInterface $big)
-    {
-        $this->big = $big;
-
-        return $this;
-    }
-
     /**
      * {@inheritdoc}
      */
diff --git a/src/Search.php b/src/Search.php
index b9d00705..cb09912d 100644
--- a/src/Search.php
+++ b/src/Search.php
@@ -28,6 +28,7 @@
 use OpenSearchDSL\SearchEndpoint\SuggestEndpoint;
 use OpenSearchDSL\Serializer\Normalizer\CustomReferencedNormalizer;
 use OpenSearchDSL\Serializer\OrderedSerializer;
+use stdClass;
 use Symfony\Component\Serializer\Normalizer\CustomNormalizer;
 
 /**
@@ -121,6 +122,8 @@ class Search
      * URI parameters alongside Request body search.
      *
      * @link https://www.elastic.co/guide/en/elasticsearch/reference/current/search-uri-request.html
+     *
+     * @var array<string, string|array|bool>
      */
     private array $uriParams = [];
 
@@ -140,29 +143,20 @@ class Search
      */
     private array $endpoints = [];
 
-    /**
-     * Constructor to initialize static properties
-     */
     public function __construct()
     {
         $this->initializeSerializer();
     }
 
-    /**
-     * Wakeup method to initialize static properties
-     */
     public function __wakeup()
     {
         $this->initializeSerializer();
     }
 
-    /**
-     * Initializes the serializer
-     */
-    private function initializeSerializer()
+    private function initializeSerializer(): void
     {
-        if (static::$serializer === null) {
-            static::$serializer = new OrderedSerializer(
+        if (self::$serializer === null) {
+            self::$serializer = new OrderedSerializer(
                 [
                     new CustomReferencedNormalizer(),
                     new CustomNormalizer(),
@@ -176,19 +170,12 @@ private function initializeSerializer()
      *
      * @param string $type Endpoint type.
      */
-    public function destroyEndpoint($type)
+    public function destroyEndpoint(string $type): void
     {
         unset($this->endpoints[$type]);
     }
 
-    /**
-     * Adds query to the search.
-     *
-     * @param string           $boolType
-     * @param string           $key
-     * @return $this
-     */
-    public function addQuery(BuilderInterface $query, $boolType = BoolQuery::MUST, $key = null)
+    public function addQuery(BuilderInterface $query, string $boolType = BoolQuery::MUST, ?string $key = null): self
     {
         $endpoint = $this->getEndpoint(QueryEndpoint::NAME);
         $endpoint->addToBool($query, $boolType, $key);
@@ -196,28 +183,15 @@ public function addQuery(BuilderInterface $query, $boolType = BoolQuery::MUST, $
         return $this;
     }
 
-    /**
-     * Returns endpoint instance.
-     *
-     * @param string $type Endpoint type.
-     *
-     * @return SearchEndpointInterface
-     */
-    private function getEndpoint($type)
+    private function getEndpoint(string $type): SearchEndpointInterface
     {
-        if (!array_key_exists($type, $this->endpoints)) {
-            $this->endpoints[$type] = SearchEndpointFactory::get($type);
-        }
-
-        return $this->endpoints[$type];
+        return $this->endpoints[$type] ??= SearchEndpointFactory::get($type);
     }
 
     /**
      * Returns queries inside BoolQuery instance.
-     *
-     * @return BoolQuery
      */
-    public function getQueries()
+    public function getQueries(): ?BoolQuery
     {
         $endpoint = $this->getEndpoint(QueryEndpoint::NAME);
 
@@ -226,11 +200,8 @@ public function getQueries()
 
     /**
      * Sets query endpoint parameters.
-     *
-     *
-     * @return $this
      */
-    public function setQueryParameters(array $parameters)
+    public function setQueryParameters(array $parameters): self
     {
         $this->setEndpointParameters(QueryEndpoint::NAME, $parameters);
 
@@ -240,11 +211,9 @@ public function setQueryParameters(array $parameters)
     /**
      * Sets parameters to the endpoint.
      *
-     * @param string $endpointName
-     *
-     * @return $this
+     * @param array<string, array|string|int|float|bool|stdClass> $parameters
      */
-    public function setEndpointParameters($endpointName, array $parameters)
+    public function setEndpointParameters(string $endpointName, array $parameters): self
     {
         /** @var AbstractSearchEndpoint $endpoint */
         $endpoint = $this->getEndpoint($endpointName);
@@ -255,18 +224,12 @@ public function setEndpointParameters($endpointName, array $parameters)
 
     /**
      * Adds a post filter to search.
-     *
-     * @param BuilderInterface $filter   Filter.
-     * @param string           $boolType Example boolType values:
-     *                                   - must
-     *                                   - must_not
-     *                                   - should.
-     * @param string           $key
-     *
-     * @return $this.
      */
-    public function addPostFilter(BuilderInterface $filter, $boolType = BoolQuery::MUST, $key = null)
-    {
+    public function addPostFilter(
+        BuilderInterface $filter,
+        string $boolType = BoolQuery::MUST,
+        ?string $key = null
+    ): self {
         $this
             ->getEndpoint(PostFilterEndpoint::NAME)
             ->addToBool($filter, $boolType, $key);
@@ -276,10 +239,8 @@ public function addPostFilter(BuilderInterface $filter, $boolType = BoolQuery::M
 
     /**
      * Returns queries inside BoolFilter instance.
-     *
-     * @return BoolQuery
      */
-    public function getPostFilters()
+    public function getPostFilters(): ?BoolQuery
     {
         $endpoint = $this->getEndpoint(PostFilterEndpoint::NAME);
 
@@ -288,11 +249,8 @@ public function getPostFilters()
 
     /**
      * Sets post filter endpoint parameters.
-     *
-     *
-     * @return $this
      */
-    public function setPostFilterParameters(array $parameters)
+    public function setPostFilterParameters(array $parameters): self
     {
         $this->setEndpointParameters(PostFilterEndpoint::NAME, $parameters);
 
@@ -301,11 +259,8 @@ public function setPostFilterParameters(array $parameters)
 
     /**
      * Adds aggregation into search.
-     *
-     *
-     * @return $this
      */
-    public function addAggregation(AbstractAggregation $aggregation)
+    public function addAggregation(AbstractAggregation $aggregation): self
     {
         $this->getEndpoint(AggregationsEndpoint::NAME)->add($aggregation, $aggregation->getName());
 
@@ -317,18 +272,15 @@ public function addAggregation(AbstractAggregation $aggregation)
      *
      * @return BuilderInterface[]
      */
-    public function getAggregations()
+    public function getAggregations(): array
     {
         return $this->getEndpoint(AggregationsEndpoint::NAME)->getAll();
     }
 
     /**
      * Adds inner hit into search.
-     *
-     *
-     * @return $this
      */
-    public function addInnerHit(NestedInnerHit $innerHit)
+    public function addInnerHit(NestedInnerHit $innerHit): self
     {
         $this->getEndpoint(InnerHitsEndpoint::NAME)->add($innerHit, $innerHit->getName());
 
@@ -338,20 +290,17 @@ public function addInnerHit(NestedInnerHit $innerHit)
     /**
      * Returns all inner hits.
      *
-     * @return BuilderInterface[]
+     * @return array<string, BuilderInterface>
      */
-    public function getInnerHits()
+    public function getInnerHits(): array
     {
         return $this->getEndpoint(InnerHitsEndpoint::NAME)->getAll();
     }
 
     /**
      * Adds sort to search.
-     *
-     *
-     * @return $this
      */
-    public function addSort(BuilderInterface $sort)
+    public function addSort(BuilderInterface $sort): self
     {
         $this->getEndpoint(SortEndpoint::NAME)->add($sort);
 
@@ -363,19 +312,15 @@ public function addSort(BuilderInterface $sort)
      *
      * @return BuilderInterface[]
      */
-    public function getSorts()
+    public function getSorts(): array
     {
         return $this->getEndpoint(SortEndpoint::NAME)->getAll();
     }
 
     /**
      * Allows to highlight search results on one or more fields.
-     *
-     * @param Highlight $highlight
-     *
-     * @return $this.
      */
-    public function addHighlight($highlight)
+    public function addHighlight(Highlight $highlight): self
     {
         $this->getEndpoint(HighlightEndpoint::NAME)->add($highlight);
 
@@ -384,10 +329,8 @@ public function addHighlight($highlight)
 
     /**
      * Returns highlight builder.
-     *
-     * @return BuilderInterface
      */
-    public function getHighlights()
+    public function getHighlights(): ?BuilderInterface
     {
         /** @var HighlightEndpoint $highlightEndpoint */
         $highlightEndpoint = $this->getEndpoint(HighlightEndpoint::NAME);
@@ -397,12 +340,8 @@ public function getHighlights()
 
     /**
     * Adds suggest into search.
-    *
-    * @param BuilderInterface $suggest
-    *
-    * @return $this
     */
-    public function addSuggest(NamedBuilderInterface $suggest)
+    public function addSuggest(NamedBuilderInterface $suggest): self
     {
         $this->getEndpoint(SuggestEndpoint::NAME)->add($suggest, $suggest->getName());
 
@@ -414,258 +353,161 @@ public function addSuggest(NamedBuilderInterface $suggest)
     *
     * @return BuilderInterface[]
     */
-    public function getSuggests()
+    public function getSuggests(): array
     {
         return $this->getEndpoint(SuggestEndpoint::NAME)->getAll();
     }
 
-    /**
-     * @return null|int
-     */
-    public function getFrom()
+    public function getFrom(): ?int
     {
         return $this->from;
     }
 
-    /**
-     * @param null|int $from
-     *
-     * @return $this
-     */
-    public function setFrom($from)
+    public function setFrom(?int $from): self
     {
         $this->from = $from;
 
         return $this;
     }
 
-    /**
-     * @return bool
-     */
-    public function isTrackTotalHits()
+    public function isTrackTotalHits(): ?bool
     {
         return $this->trackTotalHits;
     }
 
-    /**
-     * @return $this
-     */
-    public function setTrackTotalHits(bool $trackTotalHits)
+    public function setTrackTotalHits(bool $trackTotalHits): self
     {
         $this->trackTotalHits = $trackTotalHits;
 
         return $this;
     }
 
-    /**
-     * @return null|int
-     */
-    public function getSize()
+    public function getSize(): ?int
     {
         return $this->size;
     }
 
-    /**
-     * @param null|int $size
-     *
-     * @return $this
-     */
-    public function setSize($size)
+    public function setSize(?int $size): self
     {
         $this->size = $size;
 
         return $this;
     }
 
-    public function isSource(): array|bool|string
+    public function isSource(): array|bool|string|null
     {
         return $this->source;
     }
 
-    /**
-     * @return $this
-     */
-    public function setSource(array|bool|string $source)
+    public function setSource(array|bool|string $source): self
     {
         $this->source = $source;
 
         return $this;
     }
 
-    /**
-     * @return array
-     */
-    public function getStoredFields()
+    public function getStoredFields(): ?array
     {
         return $this->storedFields;
     }
 
-    /**
-     * @param array $storedFields
-     *
-     * @return $this
-     */
-    public function setStoredFields($storedFields)
+    public function setStoredFields(array $storedFields): self
     {
         $this->storedFields = $storedFields;
 
         return $this;
     }
 
-    /**
-     * @return array
-     */
-    public function getScriptFields()
+    public function getScriptFields(): ?array
     {
         return $this->scriptFields;
     }
 
-    /**
-     * @param array $scriptFields
-     *
-     * @return $this
-     */
-    public function setScriptFields($scriptFields)
+    public function setScriptFields(array $scriptFields): self
     {
         $this->scriptFields = $scriptFields;
 
         return $this;
     }
 
-    /**
-     * @return array
-     */
-    public function getDocValueFields()
+    public function getDocValueFields(): ?array
     {
         return $this->docValueFields;
     }
 
-    /**
-     * @param array $docValueFields
-     *
-     * @return $this
-     */
-    public function setDocValueFields($docValueFields)
+    public function setDocValueFields(array $docValueFields): self
     {
         $this->docValueFields = $docValueFields;
 
         return $this;
     }
 
-    /**
-     * @return bool
-     */
-    public function isExplain()
+    public function isExplain(): ?bool
     {
         return $this->explain;
     }
 
-    /**
-     * @param bool $explain
-     *
-     * @return $this
-     */
-    public function setExplain($explain)
+    public function setExplain(bool $explain): self
     {
         $this->explain = $explain;
 
         return $this;
     }
 
-    /**
-     * @return bool
-     */
-    public function isVersion()
+    public function isVersion(): ?bool
     {
         return $this->version;
     }
 
-    /**
-     * @param bool $version
-     *
-     * @return $this
-     */
-    public function setVersion($version)
+    public function setVersion(bool $version): self
     {
         $this->version = $version;
 
         return $this;
     }
 
-    /**
-     * @return array
-     */
-    public function getIndicesBoost()
+    public function getIndicesBoost(): ?array
     {
         return $this->indicesBoost;
     }
 
-    /**
-     * @param array $indicesBoost
-     *
-     * @return $this
-     */
-    public function setIndicesBoost($indicesBoost)
+    public function setIndicesBoost(array $indicesBoost): self
     {
         $this->indicesBoost = $indicesBoost;
 
         return $this;
     }
 
-    /**
-     * @return int
-     */
-    public function getMinScore()
+    public function getMinScore(): ?int
     {
         return $this->minScore;
     }
 
-    /**
-     * @param int $minScore
-     *
-     * @return $this
-     */
-    public function setMinScore($minScore)
+    public function setMinScore(int $minScore): self
     {
         $this->minScore = $minScore;
 
         return $this;
     }
 
-    /**
-     * @return array
-     */
-    public function getSearchAfter()
+    public function getSearchAfter(): ?array
     {
         return $this->searchAfter;
     }
 
-    /**
-     * @param array $searchAfter
-     *
-     * @return $this
-     */
-    public function setSearchAfter($searchAfter)
+    public function setSearchAfter(array $searchAfter): self
     {
         $this->searchAfter = $searchAfter;
 
         return $this;
     }
 
-    /**
-     * @return string
-     */
-    public function getScroll()
+    public function getScroll(): ?string
     {
         return $this->scroll;
     }
 
-    /**
-     * @param string $scroll
-     *
-     * @return $this
-     */
-    public function setScroll($scroll = '5m')
+    public function setScroll(string $scroll = '5m'): self
     {
         $this->scroll = $scroll;
 
@@ -674,12 +516,7 @@ public function setScroll($scroll = '5m')
         return $this;
     }
 
-    /**
-     * @param string $name
-     *
-     * @return $this
-     */
-    public function addUriParam($name, string|array|bool $value)
+    public function addUriParam(string $name, string|array|bool $value): self
     {
         if (in_array($name, [
             'q',
@@ -719,19 +556,16 @@ public function addUriParam($name, string|array|bool $value)
     /**
      * Returns query url parameters.
      *
-     * @return array
+     * @return array<string, string|array|bool>
      */
-    public function getUriParams()
+    public function getUriParams(): array
     {
         return $this->uriParams;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function toArray(): array
     {
-        $output = array_filter(static::$serializer->normalize($this->endpoints));
+        $output = array_filter(self::$serializer->normalize($this->endpoints));
 
         $params = [
             'from' => 'from',
diff --git a/src/SearchEndpoint/AbstractSearchEndpoint.php b/src/SearchEndpoint/AbstractSearchEndpoint.php
index cf563a78..7f15ee4c 100644
--- a/src/SearchEndpoint/AbstractSearchEndpoint.php
+++ b/src/SearchEndpoint/AbstractSearchEndpoint.php
@@ -14,6 +14,7 @@
 use BadFunctionCallException;
 use OpenSearchDSL\BuilderInterface;
 use OpenSearchDSL\ParametersTrait;
+use OpenSearchDSL\Query\Compound\BoolQuery;
 use OpenSearchDSL\Serializer\Normalizer\AbstractNormalizable;
 use OverflowException;
 
@@ -25,14 +26,14 @@ abstract class AbstractSearchEndpoint extends AbstractNormalizable implements Se
     use ParametersTrait;
 
     /**
-     * @var BuilderInterface[]
+     * @var array<string, BuilderInterface>
      */
     private array $container = [];
 
     /**
      * {@inheritdoc}
      */
-    public function add(BuilderInterface $builder, $key = null)
+    public function add(BuilderInterface $builder, $key = null): string
     {
         if (array_key_exists($key, $this->container)) {
             throw new OverflowException(sprintf('Builder with %s name for endpoint has already been added!', $key));
@@ -47,18 +48,12 @@ public function add(BuilderInterface $builder, $key = null)
         return $key;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function addToBool(BuilderInterface $builder, $boolType = null, $key = null)
+    public function addToBool(BuilderInterface $builder, string $boolType = BoolQuery::MUST, ?string $key = null): string
     {
         throw new BadFunctionCallException(sprintf("Endpoint %s doesn't support bool statements", static::NAME));
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function remove($key)
+    public function remove(string $key): static
     {
         if ($this->has($key)) {
             unset($this->container[$key]);
@@ -69,40 +64,23 @@ public function remove($key)
 
     /**
      * Checks if builder with specific key exists.
-     *
-     * @param string $key Key to check if it exists in container.
-     *
-     * @return bool
      */
-    public function has($key)
+    public function has(string $key): bool
     {
         return array_key_exists($key, $this->container);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function get($key)
+    public function get(string $key): ?BuilderInterface
     {
-        if ($this->has($key)) {
-            return $this->container[$key];
-        }
-
-        return null;
+        return $this->container[$key] ?? null;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getAll($boolType = null)
+    public function getAll(?string $boolType = null): array
     {
         return $this->container;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getBool()
+    public function getBool(): ?BoolQuery
     {
         throw new BadFunctionCallException(sprintf("Endpoint %s doesn't support bool statements", static::NAME));
     }
diff --git a/src/SearchEndpoint/HighlightEndpoint.php b/src/SearchEndpoint/HighlightEndpoint.php
index b5e33f58..9e5ef910 100644
--- a/src/SearchEndpoint/HighlightEndpoint.php
+++ b/src/SearchEndpoint/HighlightEndpoint.php
@@ -44,10 +44,7 @@ public function normalize(NormalizerInterface $normalizer, $format = null, array
         return false;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function add(BuilderInterface $builder, $key = null)
+    public function add(BuilderInterface $builder, ?string $key = null): string
     {
         if ($this->highlight !== null) {
             throw new OverflowException('Only one highlight can be set');
@@ -55,20 +52,16 @@ public function add(BuilderInterface $builder, $key = null)
 
         $this->key = $key;
         $this->highlight = $builder;
+
+        return $this->key;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getAll($boolType = null)
+    public function getAll(?string $boolType = null): array
     {
         return [$this->key => $this->highlight];
     }
 
-    /**
-     * @return BuilderInterface
-     */
-    public function getHighlight()
+    public function getHighlight(): ?BuilderInterface
     {
         return $this->highlight;
     }
diff --git a/src/SearchEndpoint/PostFilterEndpoint.php b/src/SearchEndpoint/PostFilterEndpoint.php
index 85e877b5..5060ecf7 100644
--- a/src/SearchEndpoint/PostFilterEndpoint.php
+++ b/src/SearchEndpoint/PostFilterEndpoint.php
@@ -38,7 +38,7 @@ public function normalize(NormalizerInterface $normalizer, $format = null, array
     /**
      * {@inheritdoc}
      */
-    public function getOrder()
+    public function getOrder(): int
     {
         return 1;
     }
diff --git a/src/SearchEndpoint/QueryEndpoint.php b/src/SearchEndpoint/QueryEndpoint.php
index bd586f69..d6d58f4f 100644
--- a/src/SearchEndpoint/QueryEndpoint.php
+++ b/src/SearchEndpoint/QueryEndpoint.php
@@ -27,13 +27,9 @@ class QueryEndpoint extends AbstractSearchEndpoint implements OrderedNormalizerI
     public const NAME = 'query';
 
     private ?BoolQuery $bool = null;
-
     private bool $filtersSet = false;
 
-    /**
-     * {@inheritdoc}
-     */
-    public function normalize(NormalizerInterface $normalizer, $format = null, array $context = []): array|string|int|float|bool
+    public function normalize(NormalizerInterface $normalizer, string $format = null, array $context = []): array|string|int|float|bool
     {
         if (!$this->filtersSet && $this->hasReference('filter_query')) {
             /** @var BuilderInterface $filter */
@@ -49,18 +45,12 @@ public function normalize(NormalizerInterface $normalizer, $format = null, array
         return $this->bool->toArray();
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function add(BuilderInterface $builder, $key = null)
+    public function add(BuilderInterface $builder, ?string $key = null): string
     {
         return $this->addToBool($builder, BoolQuery::MUST, $key);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function addToBool(BuilderInterface $builder, $boolType = null, $key = null)
+    public function addToBool(BuilderInterface $builder, string $boolType = BoolQuery::MUST, ?string $key = null): string
     {
         if ($this->bool === null) {
             $this->bool = new BoolQuery();
@@ -69,26 +59,17 @@ public function addToBool(BuilderInterface $builder, $boolType = null, $key = nu
         return $this->bool->add($builder, $boolType, $key);
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getOrder()
+    public function getOrder(): int
     {
         return 2;
     }
 
-    /**
-     * @return BoolQuery
-     */
-    public function getBool()
+    public function getBool(): ?BoolQuery
     {
         return $this->bool;
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function getAll($boolType = null)
+    public function getAll(?string $boolType = null): array
     {
         return $this->bool->getQueries($boolType);
     }
diff --git a/src/SearchEndpoint/SearchEndpointFactory.php b/src/SearchEndpoint/SearchEndpointFactory.php
index f0ae3d84..a0c6794e 100644
--- a/src/SearchEndpoint/SearchEndpointFactory.php
+++ b/src/SearchEndpoint/SearchEndpointFactory.php
@@ -40,7 +40,7 @@ class SearchEndpointFactory
      *
      * @throws RuntimeException Endpoint does not exist.
      */
-    public static function get($type)
+    public static function get(string $type): SearchEndpointInterface
     {
         if (!array_key_exists($type, self::$endpoints)) {
             throw new RuntimeException('Endpoint does not exist.');
diff --git a/src/SearchEndpoint/SearchEndpointInterface.php b/src/SearchEndpoint/SearchEndpointInterface.php
index fe83d7f5..b3ef1216 100644
--- a/src/SearchEndpoint/SearchEndpointInterface.php
+++ b/src/SearchEndpoint/SearchEndpointInterface.php
@@ -24,55 +24,44 @@ interface SearchEndpointInterface extends NormalizableInterface
      * Adds builder to search endpoint.
      *
      * @param BuilderInterface $builder Builder to add.
-     * @param array            $key     Additional parameters relevant to builder.
+     * @param string|null      $key     Optional key for builder to add.
      *
      * @return string Key of added builder.
      */
-    public function add(BuilderInterface $builder, $key = null);
+    public function add(BuilderInterface $builder, ?string $key = null): string;
 
     /**
      * Adds builder to search endpoint's specific bool type container.
      *
      * @param BuilderInterface $builder  Builder to add.
-     * @param array            $boolType Bool type for query or filter. If bool type is left null
-     *                                       it will be treated as MUST.
-     * @param array            $key      Additional parameters relevant to builder.
+     * @param string           $boolType Bool type for query or filter.
+     * @param string|null      $key      Additional parameters relevant to builder.
      *
      * @return string Key of added builder.
      */
-    public function addToBool(BuilderInterface $builder, $boolType = null, $key = null);
+    public function addToBool(BuilderInterface $builder, string $boolType = BoolQuery::MUST, ?string $key = null): string;
 
     /**
      * Removes contained builder.
-     *
-     * @param int $key
-     *
-     * @return $this
      */
-    public function remove($key);
+    public function remove(string $key): static;
 
     /**
      * Returns contained builder or null if Builder is not found.
-     *
-     * @param int $key
-     *
-     * @return BuilderInterface|null
      */
-    public function get($key);
+    public function get(string $key): ?BuilderInterface;
 
     /**
      * Returns contained builder or null if Builder is not found.
      *
      * @param string|null $boolType If bool type is left null it will return all builders from container.
      *
-     * @return array
+     * @return array<string, BuilderInterface>
      */
-    public function getAll($boolType = null);
+    public function getAll(?string $boolType = null): array;
 
     /**
      * Returns Bool filter or query instance with all builder objects inside.
-     *
-     * @return BoolQuery
      */
-    public function getBool();
+    public function getBool(): ?BoolQuery;
 }
diff --git a/src/SearchEndpoint/SuggestEndpoint.php b/src/SearchEndpoint/SuggestEndpoint.php
index f17ed17e..688e6ddf 100644
--- a/src/SearchEndpoint/SuggestEndpoint.php
+++ b/src/SearchEndpoint/SuggestEndpoint.php
@@ -31,7 +31,6 @@ public function normalize(NormalizerInterface $normalizer, $format = null, array
     {
         $output = [];
         if ($this->getAll() !== []) {
-            /** @var TermSuggest $suggest */
             foreach ($this->getAll() as $suggest) {
                 $output = array_merge($output, $suggest->toArray());
             }
diff --git a/src/Serializer/Normalizer/OrderedNormalizerInterface.php b/src/Serializer/Normalizer/OrderedNormalizerInterface.php
index ee471ccf..f31fdb1e 100644
--- a/src/Serializer/Normalizer/OrderedNormalizerInterface.php
+++ b/src/Serializer/Normalizer/OrderedNormalizerInterface.php
@@ -18,8 +18,6 @@ interface OrderedNormalizerInterface
 {
     /**
      * Returns normalization priority.
-     *
-     * @return int
      */
-    public function getOrder();
+    public function getOrder(): int;
 }