diff --git a/src/Body/FormPayload.php b/src/Body/FormPayload.php
index 80d0616..913ebfa 100644
--- a/src/Body/FormPayload.php
+++ b/src/Body/FormPayload.php
@@ -9,17 +9,11 @@
 
 final class FormPayload extends Map implements PayloadInterface
 {
-    /**
-     * Get the header content type value.
-     */
     public function contentType(): ?string
     {
         return 'application/x-www-form-urlencoded';
     }
 
-    /**
-     * Get the string representation of the payload.
-     */
     public function __toString()
     {
         return \http_build_query($this->all());
diff --git a/src/Body/JsonPayload.php b/src/Body/JsonPayload.php
index 877e2ee..7c80674 100644
--- a/src/Body/JsonPayload.php
+++ b/src/Body/JsonPayload.php
@@ -21,17 +21,11 @@ public function __construct(array $parameters = [], int $flags = 0)
         $this->flags = $flags;
     }
 
-    /**
-     * Get the header content type value.
-     */
     public function contentType(): ?string
     {
         return 'application/json';
     }
 
-    /**
-     * Get the string representation of the payload.
-     */
     public function __toString()
     {
         return \json_encode($this->all(), $this->flags) ?: '';
diff --git a/src/Body/MultipartPayload.php b/src/Body/MultipartPayload.php
index 738e2a5..4858905 100644
--- a/src/Body/MultipartPayload.php
+++ b/src/Body/MultipartPayload.php
@@ -17,13 +17,6 @@ final class MultipartPayload extends Map implements PayloadInterface
      */
     private $boundary;
 
-    /**
-     * Create new multipart payload instance.
-     *
-     * @param  array  $parameters
-     * @param  null|string  $boundary
-     * @return void
-     */
     public function __construct(array $parameters = [], ?string $boundary = null)
     {
         parent::__construct($parameters);
@@ -31,9 +24,6 @@ public function __construct(array $parameters = [], ?string $boundary = null)
         $this->boundary = $boundary ?: \bin2hex(\random_bytes(20));
     }
 
-    /**
-     * Get the header content type value.
-     */
     public function contentType(): ?string
     {
         return 'multipart/form-data; boundary='.$this->boundary;
@@ -94,9 +84,6 @@ private function part(string $name, $value): string
         return $str;
     }
 
-    /**
-     * Get the string representation of the payload.
-     */
     public function __toString()
     {
         $str = '';
diff --git a/src/Body/RawPayload.php b/src/Body/RawPayload.php
index 3c66185..14a5a1d 100644
--- a/src/Body/RawPayload.php
+++ b/src/Body/RawPayload.php
@@ -19,9 +19,6 @@ public function __construct(string $payload = '')
         $this->payload = $payload;
     }
 
-    /**
-     * Get the header content type value.
-     */
     public function contentType(): ?string
     {
         return null;
@@ -114,9 +111,6 @@ public function isEmpty(): bool
         return $this->payload === '';
     }
 
-    /**
-     * Get the string representation of the payload.
-     */
     public function __toString()
     {
         return $this->payload;
diff --git a/src/ConnectorConfigurator.php b/src/ConnectorConfigurator.php
index 5ebdeae..2bde60d 100644
--- a/src/ConnectorConfigurator.php
+++ b/src/ConnectorConfigurator.php
@@ -19,7 +19,7 @@
 class ConnectorConfigurator
 {
     /**
-     * @var \Closure[]
+     * @var array<\Closure(T): void>
      */
     private $handlers = [];
 
@@ -64,7 +64,6 @@ final public function middleware(callable $middleware, string $name = '')
     protected function register(\Closure $handler)
     {
         $clone = clone $this;
-
         $clone->handlers[] = $handler;
 
         return $clone;
diff --git a/src/Decoder/ChainDecoder.php b/src/Decoder/ChainDecoder.php
index 6a4775b..97c729d 100644
--- a/src/Decoder/ChainDecoder.php
+++ b/src/Decoder/ChainDecoder.php
@@ -26,6 +26,10 @@ public function __construct(iterable $decoders)
     public function decode(ResponseInterface $response): iterable
     {
         foreach ($this->decoders as $decoder) {
+            if (! $decoder instanceof DecoderInterface) {
+                throw new \InvalidArgumentException(sprintf('Decoder must implement %s. %s given', DecoderInterface::class, \get_debug_type($decoder)));
+            }
+
             try {
                 yield from $decoder->decode($response);
             } catch (NotDecodableException $e) {
diff --git a/src/Middleware.php b/src/Middleware.php
index ae5a4ff..26501c1 100644
--- a/src/Middleware.php
+++ b/src/Middleware.php
@@ -14,6 +14,9 @@ final class Middleware implements \IteratorAggregate, \Countable
      */
     private $middleware = [];
 
+    /**
+     * @param  array<array-key, callable(RequestInterface, callable): ResponseInterface> $middleware
+     */
     public function __construct(array $middleware = [])
     {
         foreach ($middleware as $name => $value) {
diff --git a/src/Middleware/Interceptor.php b/src/Middleware/Interceptor.php
index e0af739..fd9115b 100644
--- a/src/Middleware/Interceptor.php
+++ b/src/Middleware/Interceptor.php
@@ -12,6 +12,8 @@ final class Interceptor
 {
     /**
      * Add a request interceptor.
+     *
+     * @param  \Closure(RequestInterface): RequestInterface $callback
      */
     public static function request(Closure $callback): Closure
     {
@@ -22,6 +24,8 @@ public static function request(Closure $callback): Closure
 
     /**
      * Add a response interceptor.
+     *
+     * @param  \Closure(ResponseInterface): ResponseInterface $callback
      */
     public static function response(Closure $callback): Closure
     {
diff --git a/src/Retry/RetryCallback.php b/src/Retry/RetryCallback.php
index 94765dc..4002777 100644
--- a/src/Retry/RetryCallback.php
+++ b/src/Retry/RetryCallback.php
@@ -13,15 +13,19 @@
 final class RetryCallback implements RetryStrategyInterface
 {
     /**
-     * @var \Closure
+     * @var \Closure(RequestInterface, ResponseInterface): bool
      */
     private $when;
 
     /**
-     * @var \Closure
+     * @var \Closure(RetryContext): int
      */
     private $delay;
 
+    /**
+     * @param  \Closure(RequestInterface, ResponseInterface): bool $when
+     * @param  \Closure(RetryContext): int $delay
+     */
     public function __construct(Closure $when, Closure $delay)
     {
         $this->when = $when;
diff --git a/src/Traits/HasClient.php b/src/Traits/HasClient.php
index 1f51cba..df641bd 100644
--- a/src/Traits/HasClient.php
+++ b/src/Traits/HasClient.php
@@ -24,7 +24,6 @@ trait HasClient
     public function withClient(ClientInterface $client)
     {
         $clone = clone $this;
-
         $clone->client = $client;
 
         return $clone;
diff --git a/src/Traits/HasMiddleware.php b/src/Traits/HasMiddleware.php
index d372997..1e35def 100644
--- a/src/Traits/HasMiddleware.php
+++ b/src/Traits/HasMiddleware.php
@@ -5,6 +5,8 @@
 namespace Fansipan\Traits;
 
 use Fansipan\Middleware;
+use Psr\Http\Message\RequestInterface;
+use Psr\Http\Message\ResponseInterface;
 
 trait HasMiddleware
 {
@@ -29,6 +31,8 @@ public function middleware(): Middleware
 
     /**
      * Get default middleware.
+     *
+     * @return array<array-key, callable(RequestInterface, callable): ResponseInterface>
      */
     protected function defaultMiddleware(): array
     {