diff --git a/spec/Plugin/ErrorPluginSpec.php b/spec/Plugin/ErrorPluginSpec.php
index 67e5c7e..205192a 100644
--- a/spec/Plugin/ErrorPluginSpec.php
+++ b/spec/Plugin/ErrorPluginSpec.php
@@ -27,7 +27,7 @@ public function it_is_a_plugin()
 
     public function it_throw_client_error_exception_on_4xx_error(RequestInterface $request, ResponseInterface $response)
     {
-        $response->getStatusCode()->willReturn('400');
+        $response->getStatusCode()->willReturn(400);
         $response->getReasonPhrase()->willReturn('Bad request');
 
         $next = function (RequestInterface $receivedRequest) use ($request, $response) {
@@ -45,7 +45,7 @@ public function it_does_not_throw_client_error_exception_on_4xx_error_if_only_se
     {
         $this->beConstructedWith(['only_server_exception' => true]);
 
-        $response->getStatusCode()->willReturn('400');
+        $response->getStatusCode()->willReturn(400);
         $response->getReasonPhrase()->willReturn('Bad request');
 
         $next = function (RequestInterface $receivedRequest) use ($request, $response) {
@@ -59,7 +59,7 @@ public function it_does_not_throw_client_error_exception_on_4xx_error_if_only_se
 
     public function it_throw_server_error_exception_on_5xx_error(RequestInterface $request, ResponseInterface $response)
     {
-        $response->getStatusCode()->willReturn('500');
+        $response->getStatusCode()->willReturn(500);
         $response->getReasonPhrase()->willReturn('Server error');
 
         $next = function (RequestInterface $receivedRequest) use ($request, $response) {
@@ -75,7 +75,7 @@ public function it_throw_server_error_exception_on_5xx_error(RequestInterface $r
 
     public function it_returns_response(RequestInterface $request, ResponseInterface $response)
     {
-        $response->getStatusCode()->willReturn('200');
+        $response->getStatusCode()->willReturn(200);
 
         $next = function (RequestInterface $receivedRequest) use ($request, $response) {
             if (Argument::is($request->getWrappedObject())->scoreArgument($receivedRequest)) {
diff --git a/spec/Plugin/RedirectPluginSpec.php b/spec/Plugin/RedirectPluginSpec.php
index de9b30a..3342f60 100644
--- a/spec/Plugin/RedirectPluginSpec.php
+++ b/spec/Plugin/RedirectPluginSpec.php
@@ -37,7 +37,7 @@ public function it_redirects_on_302(
         ResponseInterface $finalResponse,
         Promise $promise
     ) {
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(true);
         $responseRedirect->getHeaderLine('Location')->willReturn('/redirect');
 
@@ -156,7 +156,7 @@ public function it_replace_full_url(
         $request->getUri()->willReturn($uri);
         $uri->__toString()->willReturn('/original');
 
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(true);
         $responseRedirect->getHeaderLine('Location')->willReturn('https://server.com:8000/redirect?query#fragment');
 
@@ -203,7 +203,7 @@ public function it_throws_http_exception_on_no_location(RequestInterface $reques
 
         $request->getUri()->willReturn($uri);
         $uri->__toString()->willReturn('/original');
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(false);
 
         $promise = $this->handleRequest($request, $next, function () {});
@@ -223,7 +223,7 @@ public function it_throws_http_exception_on_invalid_location(RequestInterface $r
         $uri->__toString()->willReturn('/original');
         $responseRedirect->getHeaderLine('Location')->willReturn('scheme:///invalid');
 
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(true);
 
         $promise = $this->handleRequest($request, $next, function () {});
@@ -240,7 +240,7 @@ public function it_throw_multi_redirect_exception_on_300(RequestInterface $reque
         };
 
         $this->beConstructedWith(['preserve_header' => true, 'use_default_for_multiple' => false]);
-        $responseRedirect->getStatusCode()->willReturn('300');
+        $responseRedirect->getStatusCode()->willReturn(300);
 
         $promise = $this->handleRequest($request, $next, function () {});
         $promise->shouldReturnAnInstanceOf(HttpRejectedPromise::class);
@@ -255,7 +255,7 @@ public function it_throw_multi_redirect_exception_on_300_if_no_location(RequestI
             }
         };
 
-        $responseRedirect->getStatusCode()->willReturn('300');
+        $responseRedirect->getStatusCode()->willReturn(300);
         $responseRedirect->hasHeader('Location')->willReturn(false);
 
         $promise = $this->handleRequest($request, $next, function () {});
@@ -275,7 +275,7 @@ public function it_switch_method_for_302(
         $request->getUri()->willReturn($uri);
         $uri->__toString()->willReturn('/original');
 
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(true);
         $responseRedirect->getHeaderLine('Location')->willReturn('/redirect');
 
@@ -324,7 +324,7 @@ public function it_clears_headers(
         $request->getUri()->willReturn($uri);
         $uri->__toString()->willReturn('/original');
 
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(true);
         $responseRedirect->getHeaderLine('Location')->willReturn('/redirect');
 
@@ -468,7 +468,7 @@ public function it_redirects_http_to_https(
         ResponseInterface $finalResponse,
         Promise $promise
     ) {
-        $responseRedirect->getStatusCode()->willReturn('302');
+        $responseRedirect->getStatusCode()->willReturn(302);
         $responseRedirect->hasHeader('Location')->willReturn(true);
         $responseRedirect->getHeaderLine('Location')->willReturn('https://my-site.com/original');
 
diff --git a/src/Deferred.php b/src/Deferred.php
index 7c3f9f5..4c50721 100644
--- a/src/Deferred.php
+++ b/src/Deferred.php
@@ -79,7 +79,7 @@ public function getState(): string
     /**
      * Resolve this deferred with a Response.
      */
-    public function resolve(ResponseInterface $response)
+    public function resolve(ResponseInterface $response): void
     {
         if (self::PENDING !== $this->state) {
             return;
@@ -96,7 +96,7 @@ public function resolve(ResponseInterface $response)
     /**
      * Reject this deferred with an Exception.
      */
-    public function reject(Exception $exception)
+    public function reject(Exception $exception): void
     {
         if (self::PENDING !== $this->state) {
             return;
diff --git a/src/Exception/BatchException.php b/src/Exception/BatchException.php
index 5167842..46d1e47 100644
--- a/src/Exception/BatchException.php
+++ b/src/Exception/BatchException.php
@@ -28,10 +28,8 @@ public function __construct(BatchResult $result)
 
     /**
      * Returns the BatchResult that contains all responses and exceptions.
-     *
-     * @return BatchResult
      */
-    public function getResult()
+    public function getResult(): BatchResult
     {
         return $this->result;
     }
diff --git a/src/HttpClientPool.php b/src/HttpClientPool.php
index 9e979eb..24ab421 100644
--- a/src/HttpClientPool.php
+++ b/src/HttpClientPool.php
@@ -20,5 +20,5 @@ interface HttpClientPool extends HttpAsyncClient, HttpClient
      *
      * @param ClientInterface|HttpAsyncClient|HttpClientPoolItem $client
      */
-    public function addHttpClient($client);
+    public function addHttpClient($client): void;
 }
diff --git a/src/HttpClientPool/HttpClientPool.php b/src/HttpClientPool/HttpClientPool.php
index 0c417c0..ffa21d2 100644
--- a/src/HttpClientPool/HttpClientPool.php
+++ b/src/HttpClientPool/HttpClientPool.php
@@ -27,7 +27,7 @@ abstract class HttpClientPool implements HttpClientPoolInterface
      *
      * @param ClientInterface|HttpAsyncClient|HttpClientPoolItem $client
      */
-    public function addHttpClient($client)
+    public function addHttpClient($client): void
     {
         if (!$client instanceof HttpClientPoolItem) {
             $client = new HttpClientPoolItem($client);
diff --git a/src/HttpClientPool/HttpClientPoolItem.php b/src/HttpClientPool/HttpClientPoolItem.php
index 47c9eb2..31ff569 100644
--- a/src/HttpClientPool/HttpClientPoolItem.php
+++ b/src/HttpClientPool/HttpClientPoolItem.php
@@ -144,7 +144,7 @@ public function getSendingRequestCount(): int
     /**
      * Increment the request count.
      */
-    private function incrementRequestCount()
+    private function incrementRequestCount(): void
     {
         ++$this->sendingRequestCount;
     }
@@ -152,7 +152,7 @@ private function incrementRequestCount()
     /**
      * Decrement the request count.
      */
-    private function decrementRequestCount()
+    private function decrementRequestCount(): void
     {
         --$this->sendingRequestCount;
     }
@@ -160,7 +160,7 @@ private function decrementRequestCount()
     /**
      * Enable the current client.
      */
-    private function enable()
+    private function enable(): void
     {
         $this->disabledAt = null;
     }
@@ -168,7 +168,7 @@ private function enable()
     /**
      * Disable the current client.
      */
-    private function disable()
+    private function disable(): void
     {
         $this->disabledAt = new \DateTime('now');
     }
diff --git a/src/HttpClientRouter.php b/src/HttpClientRouter.php
index 37f8c3c..ac97de0 100644
--- a/src/HttpClientRouter.php
+++ b/src/HttpClientRouter.php
@@ -45,7 +45,7 @@ public function sendAsyncRequest(RequestInterface $request)
      *
      * @param HttpClient|HttpAsyncClient $client
      */
-    public function addClient($client, RequestMatcher $requestMatcher)
+    public function addClient($client, RequestMatcher $requestMatcher): void
     {
         $this->clients[] = [
             'matcher' => $requestMatcher,
diff --git a/src/HttpClientRouterInterface.php b/src/HttpClientRouterInterface.php
index 4526e7f..ae012cf 100644
--- a/src/HttpClientRouterInterface.php
+++ b/src/HttpClientRouterInterface.php
@@ -23,5 +23,5 @@ interface HttpClientRouterInterface extends HttpClient, HttpAsyncClient
      *
      * @param ClientInterface|HttpAsyncClient $client
      */
-    public function addClient($client, RequestMatcher $requestMatcher);
+    public function addClient($client, RequestMatcher $requestMatcher): void;
 }
diff --git a/src/HttpMethodsClient.php b/src/HttpMethodsClient.php
index 9c53c71..9db9363 100644
--- a/src/HttpMethodsClient.php
+++ b/src/HttpMethodsClient.php
@@ -71,7 +71,7 @@ public function options($uri, array $headers = [], $body = null): ResponseInterf
         return $this->send('OPTIONS', $uri, $headers, $body);
     }
 
-    public function send($method, $uri, array $headers = [], $body = null): ResponseInterface
+    public function send(string $method, $uri, array $headers = [], $body = null): ResponseInterface
     {
         return $this->sendRequest($this->requestFactory->createRequest(
             $method,
diff --git a/src/HttpMethodsClientInterface.php b/src/HttpMethodsClientInterface.php
index 20fbf03..bc0829a 100644
--- a/src/HttpMethodsClientInterface.php
+++ b/src/HttpMethodsClientInterface.php
@@ -112,5 +112,5 @@ public function options($uri, array $headers = [], $body = null): ResponseInterf
      *
      * @throws Exception
      */
-    public function send($method, $uri, array $headers = [], $body = null): ResponseInterface;
+    public function send(string $method, $uri, array $headers = [], $body = null): ResponseInterface;
 }
diff --git a/src/Plugin/AddHostPlugin.php b/src/Plugin/AddHostPlugin.php
index db89d34..33ede17 100644
--- a/src/Plugin/AddHostPlugin.php
+++ b/src/Plugin/AddHostPlugin.php
@@ -66,7 +66,7 @@ public function handleRequest(RequestInterface $request, callable $next, callabl
         return $next($request);
     }
 
-    private function configureOptions(OptionsResolver $resolver)
+    private function configureOptions(OptionsResolver $resolver): void
     {
         $resolver->setDefaults([
             'replace' => false,
diff --git a/src/Plugin/CookiePlugin.php b/src/Plugin/CookiePlugin.php
index 8399210..2ec5265 100644
--- a/src/Plugin/CookiePlugin.php
+++ b/src/Plugin/CookiePlugin.php
@@ -91,11 +91,9 @@ public function handleRequest(RequestInterface $request, callable $next, callabl
     /**
      * Creates a cookie from a string.
      *
-     * @return Cookie|null
-     *
      * @throws TransferException
      */
-    private function createCookie(RequestInterface $request, string $setCookieHeader)
+    private function createCookie(RequestInterface $request, string $setCookieHeader): ?Cookie
     {
         $parts = array_map('trim', explode(';', $setCookieHeader));
 
@@ -168,6 +166,8 @@ private function createCookie(RequestInterface $request, string $setCookieHeader
      * Separates key/value pair from cookie.
      *
      * @param string $part A single cookie value in format key=value
+     *
+     * @return string[]
      */
     private function createValueKey(string $part): array
     {
diff --git a/src/Plugin/RedirectPlugin.php b/src/Plugin/RedirectPlugin.php
index e562553..061f35b 100644
--- a/src/Plugin/RedirectPlugin.php
+++ b/src/Plugin/RedirectPlugin.php
@@ -9,7 +9,6 @@
 use Http\Client\Common\Plugin;
 use Http\Client\Exception\HttpException;
 use Http\Promise\Promise;
-use Psr\Http\Message\MessageInterface;
 use Psr\Http\Message\RequestInterface;
 use Psr\Http\Message\ResponseInterface;
 use Psr\Http\Message\UriInterface;
@@ -98,7 +97,7 @@ final class RedirectPlugin implements Plugin
     private $useDefaultForMultiple;
 
     /**
-     * @var array
+     * @var string[][] Chain identifier => list of URLs for this chain
      */
     private $circularDetection = [];
 
@@ -180,63 +179,51 @@ public function handleRequest(RequestInterface $request, callable $next, callabl
         });
     }
 
-    /**
-     * Builds the redirect request.
-     *
-     * @param RequestInterface $request    Original request
-     * @param UriInterface     $uri        New uri
-     * @param int              $statusCode Status code from the redirect response
-     *
-     * @return MessageInterface|RequestInterface
-     */
-    private function buildRedirectRequest(RequestInterface $request, UriInterface $uri, $statusCode)
+    private function buildRedirectRequest(RequestInterface $originalRequest, UriInterface $targetUri, int $statusCode): RequestInterface
     {
-        $request = $request->withUri($uri);
+        $originalRequest = $originalRequest->withUri($targetUri);
 
-        if (false !== $this->redirectCodes[$statusCode]['switch'] && !in_array($request->getMethod(), $this->redirectCodes[$statusCode]['switch']['unless'])) {
-            $request = $request->withMethod($this->redirectCodes[$statusCode]['switch']['to']);
+        if (false !== $this->redirectCodes[$statusCode]['switch'] && !in_array($originalRequest->getMethod(), $this->redirectCodes[$statusCode]['switch']['unless'])) {
+            $originalRequest = $originalRequest->withMethod($this->redirectCodes[$statusCode]['switch']['to']);
         }
 
         if (is_array($this->preserveHeader)) {
-            $headers = array_keys($request->getHeaders());
+            $headers = array_keys($originalRequest->getHeaders());
 
             foreach ($headers as $name) {
                 if (!in_array($name, $this->preserveHeader)) {
-                    $request = $request->withoutHeader($name);
+                    $originalRequest = $originalRequest->withoutHeader($name);
                 }
             }
         }
 
-        return $request;
+        return $originalRequest;
     }
 
     /**
      * Creates a new Uri from the old request and the location header.
      *
-     * @param ResponseInterface $response The redirect response
-     * @param RequestInterface  $request  The original request
-     *
      * @throws HttpException                If location header is not usable (missing or incorrect)
      * @throws MultipleRedirectionException If a 300 status code is received and default location cannot be resolved (doesn't use the location header or not present)
      */
-    private function createUri(ResponseInterface $response, RequestInterface $request): UriInterface
+    private function createUri(ResponseInterface $redirectResponse, RequestInterface $originalRequest): UriInterface
     {
-        if ($this->redirectCodes[$response->getStatusCode()]['multiple'] && (!$this->useDefaultForMultiple || !$response->hasHeader('Location'))) {
-            throw new MultipleRedirectionException('Cannot choose a redirection', $request, $response);
+        if ($this->redirectCodes[$redirectResponse->getStatusCode()]['multiple'] && (!$this->useDefaultForMultiple || !$redirectResponse->hasHeader('Location'))) {
+            throw new MultipleRedirectionException('Cannot choose a redirection', $originalRequest, $redirectResponse);
         }
 
-        if (!$response->hasHeader('Location')) {
-            throw new HttpException('Redirect status code, but no location header present in the response', $request, $response);
+        if (!$redirectResponse->hasHeader('Location')) {
+            throw new HttpException('Redirect status code, but no location header present in the response', $originalRequest, $redirectResponse);
         }
 
-        $location = $response->getHeaderLine('Location');
+        $location = $redirectResponse->getHeaderLine('Location');
         $parsedLocation = parse_url($location);
 
         if (false === $parsedLocation) {
-            throw new HttpException(sprintf('Location %s could not be parsed', $location), $request, $response);
+            throw new HttpException(sprintf('Location %s could not be parsed', $location), $originalRequest, $redirectResponse);
         }
 
-        $uri = $request->getUri();
+        $uri = $originalRequest->getUri();
 
         if (array_key_exists('scheme', $parsedLocation)) {
             $uri = $uri->withScheme($parsedLocation['scheme']);