diff --git a/phpstan.neon b/phpstan.neon
index 6d55e95..c3ece0f 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -2,7 +2,7 @@ includes:
     - vendor/phpstan/phpstan-phpunit/extension.neon
     - vendor/phpstan/phpstan-phpunit/rules.neon
     - lib/phpstan/phpstan.neon
-	- vendor/phpat/phpat/extension.neon
+    - vendor/phpat/phpat/extension.neon
 
 parameters:
 	bootstrapFiles:
diff --git a/src/ArtyCodingStandard/PHPAt/CleanArchitectureTest.php b/src/ArtyCodingStandard/PHPAt/CleanArchitectureTest.php
new file mode 100644
index 0000000..a5a1f1e
--- /dev/null
+++ b/src/ArtyCodingStandard/PHPAt/CleanArchitectureTest.php
@@ -0,0 +1,78 @@
+<?php
+
+declare(strict_types=1);
+
+namespace ArtyCodingStandard\PHPAt;
+
+use PHPat\Selector\Selector;
+use PHPat\Test\Builder\Rule;
+use PHPat\Test\PHPat;
+
+final class CleanArchitectureTest
+{
+    public function testDomainDoesNotDependOnApplication(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Domain'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('App\Application'))
+            ->because('Domain is the core layer and must remain independent of outer layers');
+    }
+
+    public function testDomainDoesNotDependOnInfrastructure(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Domain'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('App\Infrastructure'))
+            ->because('Domain must not know about infrastructure concerns (DB, HTTP, etc.)');
+    }
+
+    public function testDomainDoesNotDependOnSymfony(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Domain'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('Symfony'))
+            ->because('Domain must be framework-agnostic');
+    }
+
+    public function testDomainDoesNotDependOnDoctrine(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Domain'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('Doctrine'))
+            ->because('Domain must not depend on persistence concerns');
+    }
+
+    public function testApplicationDoesNotDependOnInfrastructure(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Application'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('App\Infrastructure'))
+            ->because('Application layer must depend on Domain abstractions, not Infrastructure implementations');
+    }
+
+    public function testApplicationDoesNotDependOnSymfony(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Application'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('Symfony'))
+            ->because('Application use-cases must be framework-agnostic');
+    }
+
+    public function testApplicationDoesNotDependOnDoctrine(): Rule
+    {
+        return PHPat::rule()
+            ->classes(Selector::inNamespace('App\Application'))
+            ->shouldNotDependOn()
+            ->classes(Selector::inNamespace('Doctrine'))
+            ->because(
+                'Application layer must not depend on persistence concerns'
+                . ' — use Domain repository interfaces instead'
+            );
+    }
+}