diff --git a/composer.json b/composer.json
index 3aacdd31..1a8dd68b 100644
--- a/composer.json
+++ b/composer.json
@@ -22,14 +22,18 @@
         }
     ],
     "require": {
+        "php": ">=7.1",
         "ext-json": "*",
         "monolog/monolog": "^1.24",
-        "php": ">=7.1",
         "php-di/php-di": "^6.0",
+
         "slim/psr7": "^0.5",
         "slim/slim": "^4.1"
     },
     "require-dev": {
+        "phpstan/phpstan": "@stable",
+        "phpstan/phpstan-deprecation-rules": "@stable",
+        "phpstan/phpstan-strict-rules": "@stable",
         "phpunit/phpunit": "^7.5"
     },
     "config": {
@@ -47,6 +51,7 @@
         }
     },
     "scripts": {
+        "phpstan": "./vendor/bin/phpstan analyse --level 3 --configuration phpstan.neon app src",
         "start": "php -S localhost:8080 -t public",
         "test": "phpunit"
     }
diff --git a/phpstan.neon b/phpstan.neon
new file mode 100644
index 00000000..8cf8a641
--- /dev/null
+++ b/phpstan.neon
@@ -0,0 +1,5 @@
+includes:
+    - ./vendor/phpstan/phpstan-deprecation-rules/rules.neon
+    - ./vendor/phpstan/phpstan-strict-rules/rules.neon
+parameters:
+    inferPrivatePropertyTypeFromConstructor: true
diff --git a/src/Application/Handlers/ShutdownHandler.php b/src/Application/Handlers/ShutdownHandler.php
index 323f16af..143d51e2 100644
--- a/src/Application/Handlers/ShutdownHandler.php
+++ b/src/Application/Handlers/ShutdownHandler.php
@@ -24,13 +24,6 @@ class ShutdownHandler
      */
     private $displayErrorDetails;
 
-    /**
-     * ShutdownHandler constructor.
-     *
-     * @param Request       $request
-     * @param $errorHandler $errorHandler
-     * @param bool          $displayErrorDetails
-     */
     public function __construct(
         Request $request,
         HttpErrorHandler $errorHandler,
@@ -41,10 +34,10 @@ public function __construct(
         $this->displayErrorDetails = $displayErrorDetails;
     }
 
-    public function __invoke()
+    public function __invoke() : void
     {
         $error = error_get_last();
-        if ($error) {
+        if (is_array($error)) {
             $errorFile = $error['file'];
             $errorLine = $error['line'];
             $errorMessage = $error['message'];
diff --git a/src/Domain/User/UserNotFoundException.php b/src/Domain/User/UserNotFoundException.php
index 2080774a..6c350ed3 100644
--- a/src/Domain/User/UserNotFoundException.php
+++ b/src/Domain/User/UserNotFoundException.php
@@ -7,5 +7,8 @@
 
 class UserNotFoundException extends DomainRecordNotFoundException
 {
+    /**
+     * @var string
+     */
     public $message = 'The user you requested does not exist.';
 }