diff --git a/.github/workflows/tests.yml b/.github/workflows/tests.yml
index ba38486..0b6a230 100644
--- a/.github/workflows/tests.yml
+++ b/.github/workflows/tests.yml
@@ -1,9 +1,24 @@
 name: CI
 on:
     - push
-    - pull_request
 jobs:
-    build:
+    phpstan:
+        runs-on: ubuntu-latest
+        steps:
+            -   name: Checkout
+                uses: actions/checkout@v2
+
+            -   name: Setup PHP, with composer and extensions
+                uses: shivammathur/setup-php@v2
+                with:
+                    php-version: 7.3
+
+            -   name: Install dependencies with Composer
+                uses: ramsey/composer-install@v1
+
+            -   name: Run phpstan
+                run: vendor/bin/phpstan analyse --level=6 src/
+    tests:
         strategy:
             matrix:
                 dependencies:
@@ -13,6 +28,7 @@ jobs:
                     - 7.3
                     - 7.4
                     - 8.0
+                    - 8.1
         runs-on: ubuntu-latest
         steps:
             -   name: Checkout
diff --git a/composer.json b/composer.json
index 15db6bf..77bcca9 100644
--- a/composer.json
+++ b/composer.json
@@ -16,9 +16,8 @@
         "maximebf/debugbar": "^1.4",
         "psr/http-server-handler": "^1.0",
         "psr/http-server-middleware": "^1.0",
-        "psr/container": "^1.0",
-        "psr/http-message": "^1.0.1",
-        "psr/http-factory": "^1.0",
+        "psr/container-implementation": "^1.0 || ^2.0",
+        "psr/http-message-implementation": "^1.0",
         "psr/http-factory-implementation": "^1.0"
     },
     "require-dev": {
@@ -28,7 +27,8 @@
         "mezzio/mezzio": "^3.0",
         "mezzio/mezzio-fastroute": "^3.0.1",
         "laminas/laminas-servicemanager": "^3.3.2",
-        "laminas/laminas-diactoros": "^2.0"
+        "laminas/laminas-diactoros": "^2.0",
+        "phpstan/phpstan": "^1.4"
     },
     "autoload": {
         "psr-4": {
diff --git a/phpunit.xml b/phpunit.xml
index b0c7e5f..fd2da66 100644
--- a/phpunit.xml
+++ b/phpunit.xml
@@ -1,15 +1,13 @@
 <?xml version="1.0" encoding="UTF-8"?>
-
-<phpunit bootstrap="./vendor/autoload.php" colors="true">
-    <testsuites>
-        <testsuite name="unit">
-            <directory>./test</directory>
-        </testsuite>
-    </testsuites>
-
-    <filter>
-        <whitelist processUncoveredFilesFromWhitelist="true">
-            <directory suffix=".php">./src</directory>
-        </whitelist>
-    </filter>
+<phpunit xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" bootstrap="./vendor/autoload.php" colors="true" xsi:noNamespaceSchemaLocation="vendor/phpunit/phpunit/phpunit.xsd">
+  <coverage processUncoveredFiles="true">
+    <include>
+      <directory suffix=".php">./src</directory>
+    </include>
+  </coverage>
+  <testsuites>
+    <testsuite name="unit">
+      <directory>./test</directory>
+    </testsuite>
+  </testsuites>
 </phpunit>
diff --git a/src/ConfigProvider.php b/src/ConfigProvider.php
index 6204d59..375bad1 100644
--- a/src/ConfigProvider.php
+++ b/src/ConfigProvider.php
@@ -5,11 +5,17 @@
 
 final class ConfigProvider
 {
+    /**
+     * @return array<string, mixed>
+     */
     public static function getConfig(): array
     {
         return (new self())();
     }
 
+    /**
+     * @return array<string, mixed>
+     */
     public function __invoke(): array
     {
         $config = include __DIR__ . '/../config/phpdebugbar.config.php';
diff --git a/src/JavascriptRendererFactory.php b/src/JavascriptRendererFactory.php
index c47fef0..3063abc 100644
--- a/src/JavascriptRendererFactory.php
+++ b/src/JavascriptRendererFactory.php
@@ -11,11 +11,11 @@ final class JavascriptRendererFactory
 {
     public function __invoke(ContainerInterface $container): JavascriptRenderer
     {
-        $debugbar = $container->get(DebugBar::class);
+        $debugBar = $container->get(DebugBar::class);
         $config = $container->get(ConfigProvider::class);
         $rendererOptions = $config['phpmiddleware']['phpdebugbar']['javascript_renderer'];
 
-        $renderer = new JavascriptRenderer($debugbar);
+        $renderer = new JavascriptRenderer($debugBar);
         $renderer->setOptions($rendererOptions);
 
         return $renderer;
diff --git a/src/PhpDebugBarMiddleware.php b/src/PhpDebugBarMiddleware.php
index 6bdc2f6..8d4a892 100644
--- a/src/PhpDebugBarMiddleware.php
+++ b/src/PhpDebugBarMiddleware.php
@@ -21,16 +21,27 @@ final class PhpDebugBarMiddleware implements MiddlewareInterface
 {
     public const FORCE_KEY = 'X-Enable-Debug-Bar';
 
+    /**
+     * @var DebugBarRenderer
+     */
     private $debugBarRenderer;
+
+    /**
+     * @var ResponseFactoryInterface
+     */
     private $responseFactory;
+
+    /**
+     * @var StreamFactoryInterface
+     */
     private $streamFactory;
 
     public function __construct(
-        DebugBarRenderer $debugbarRenderer,
+        DebugBarRenderer $debugBarRenderer,
         ResponseFactoryInterface $responseFactory,
         StreamFactoryInterface $streamFactory
     ) {
-        $this->debugBarRenderer = $debugbarRenderer;
+        $this->debugBarRenderer = $debugBarRenderer;
         $this->responseFactory = $responseFactory;
         $this->streamFactory = $streamFactory;
     }
@@ -60,7 +71,14 @@ public function process(ServerRequest $request, RequestHandler $handler): Respon
     public function __invoke(ServerRequest $request, Response $response, callable $next): Response
     {
         $handler = new class($next, $response) implements RequestHandler {
+            /**
+             * @var callable
+             */
             private $next;
+
+            /**
+             * @var Response
+             */
             private $response;
 
             public function __construct(callable $next, Response $response)
@@ -81,9 +99,9 @@ private function shouldReturnResponse(ServerRequest $request, Response $response
     {
         $forceHeaderValue = $request->getHeaderLine(self::FORCE_KEY);
         $forceCookieValue = $request->getCookieParams()[self::FORCE_KEY] ?? '';
-        $forceAttibuteValue = $request->getAttribute(self::FORCE_KEY, '');
-        $isForceEnable = in_array('true', [$forceHeaderValue, $forceCookieValue, $forceAttibuteValue], true);
-        $isForceDisable = in_array('false', [$forceHeaderValue, $forceCookieValue, $forceAttibuteValue], true);
+        $forceAttributeValue = $request->getAttribute(self::FORCE_KEY, '');
+        $isForceEnable = in_array('true', [$forceHeaderValue, $forceCookieValue, $forceAttributeValue], true);
+        $isForceDisable = in_array('false', [$forceHeaderValue, $forceCookieValue, $forceAttributeValue], true);
 
         return $isForceDisable || (!$isForceEnable && ($this->isRedirect($response) || !$this->isHtmlAccepted($request)));
     }
@@ -169,22 +187,22 @@ private function getContentTypeByFileName(string $filename): string
             'woff2' => 'application/font-woff2',
         ];
 
-        return isset($map[$ext]) ? $map[$ext] : 'text/plain';
+        return $map[$ext] ?? 'text/plain';
     }
 
     private function isHtmlResponse(Response $response): bool
     {
-        return $this->hasHeaderContains($response, 'Content-Type', 'text/html');
+        return $this->isHtml($response, 'Content-Type');
     }
 
     private function isHtmlAccepted(ServerRequest $request): bool
     {
-        return $this->hasHeaderContains($request, 'Accept', 'text/html');
+        return $this->isHtml($request, 'Accept');
     }
 
-    private function hasHeaderContains(MessageInterface $message, string $headerName, string $value): bool
+    private function isHtml(MessageInterface $message, string $headerName): bool
     {
-        return strpos($message->getHeaderLine($headerName), $value) !== false;
+        return strpos($message->getHeaderLine($headerName), 'text/html') !== false;
     }
 
     private function isRedirect(Response $response): bool
@@ -216,6 +234,9 @@ private function serializeResponse(Response $response) : string
         );
     }
 
+    /**
+     * @param array<string, array<string>> $headers
+     */
     private function serializeHeaders(array $headers) : string
     {
         $lines = [];