diff --git a/README.md b/README.md
index 882dc41a..1ad2a7c2 100644
--- a/README.md
+++ b/README.md
@@ -368,10 +368,12 @@ You can add multiple parameters, the violation will happen when one of them matc
 ```php
 $rules[] = Rule::allClasses()
     ->that(new ResideInOneOfTheseNamespaces('App\Domain'))
-    ->should(new NotHaveDependencyOutsideNamespace('App\Domain', ['Ramsey\Uuid'], true))
+    ->should(new NotHaveDependencyOutsideNamespace('App\Domain', ['Ramsey\Uuid']))
     ->because('we want protect our domain except for Ramsey\Uuid');
 ```
 
+Note: PHP core classes (e.g., `DateTime`, `Exception`, `PDO`) are automatically excluded from dependency checks.
+
 ### Not have a name matching a pattern
 
 ```php
diff --git a/src/Analyzer/ClassDescriptionBuilder.php b/src/Analyzer/ClassDescriptionBuilder.php
index fb137d3e..a3a54700 100644
--- a/src/Analyzer/ClassDescriptionBuilder.php
+++ b/src/Analyzer/ClassDescriptionBuilder.php
@@ -78,6 +78,11 @@ public function addInterface(string $FQCN, int $line): self
 
     public function addDependency(ClassDependency $cd): self
     {
+        // Filter out PHP core classes
+        if ($this->isPhpCoreClass($cd)) {
+            return $this;
+        }
+
         $this->classDependencies[] = $cd;
 
         return $this;
@@ -169,4 +174,26 @@ public function build(): ClassDescription
             $this->filePath
         );
     }
+
+    /**
+     * Checks if a dependency is a PHP core/internal class.
+     * Uses Reflection to detect PHP built-in classes from core and extensions
+     * (e.g., DateTime, Exception, MongoDB\Driver\Manager, Swoole\Server).
+     */
+    private function isPhpCoreClass(ClassDependency $dependency): bool
+    {
+        $fqcn = $dependency->getFQCN();
+
+        try {
+            /** @var class-string $className */
+            $className = $fqcn->toString();
+            $reflection = new \ReflectionClass($className);
+
+            return $reflection->isInternal();
+        } catch (\ReflectionException $e) {
+            // Class doesn't exist in the current environment
+            // It's likely a user-defined class in the project being analyzed
+            return false;
+        }
+    }
 }
diff --git a/src/Expression/ForClasses/NotHaveDependencyOutsideNamespace.php b/src/Expression/ForClasses/NotHaveDependencyOutsideNamespace.php
index 4501d6e1..24fa721b 100644
--- a/src/Expression/ForClasses/NotHaveDependencyOutsideNamespace.php
+++ b/src/Expression/ForClasses/NotHaveDependencyOutsideNamespace.php
@@ -19,13 +19,10 @@ class NotHaveDependencyOutsideNamespace implements Expression
     /** @var array<string> */
     private array $externalDependenciesToExclude;
 
-    private bool $excludeCoreNamespace;
-
-    public function __construct(string $namespace, array $externalDependenciesToExclude = [], bool $excludeCoreNamespace = false)
+    public function __construct(string $namespace, array $externalDependenciesToExclude = [])
     {
         $this->namespace = $namespace;
         $this->externalDependenciesToExclude = $externalDependenciesToExclude;
-        $this->excludeCoreNamespace = $excludeCoreNamespace;
     }
 
     public function describe(ClassDescription $theClass, string $because): Description
@@ -49,10 +46,6 @@ public function evaluate(ClassDescription $theClass, Violations $violations, str
                 continue;
             }
 
-            if ($this->excludeCoreNamespace && '' === $externalDep->getFQCN()->namespace()) {
-                continue;
-            }
-
             $violation = Violation::createWithErrorLine(
                 $theClass->getFQCN(),
                 ViolationMessage::withDescription(
diff --git a/tests/Unit/Analyzer/ClassDescriptionBuilderTest.php b/tests/Unit/Analyzer/ClassDescriptionBuilderTest.php
index 21a55e40..a12ba3a5 100644
--- a/tests/Unit/Analyzer/ClassDescriptionBuilderTest.php
+++ b/tests/Unit/Analyzer/ClassDescriptionBuilderTest.php
@@ -180,4 +180,101 @@ public function test_it_should_create_not_trait(): void
         self::assertInstanceOf(ClassDescription::class, $classDescription);
         self::assertFalse($classDescription->isTrait());
     }
+
+    public function test_it_should_filter_out_php_core_classes(): void
+    {
+        $FQCN = 'MyClass';
+
+        $classDescription = (new ClassDescriptionBuilder())
+            ->setFilePath('src/Foo.php')
+            ->setClassName($FQCN)
+            ->addDependency(new ClassDependency('DateTime', 10))
+            ->addDependency(new ClassDependency('Exception', 15))
+            ->addDependency(new ClassDependency('PDO', 20))
+            ->build();
+
+        self::assertInstanceOf(ClassDescription::class, $classDescription);
+
+        // PHP core classes should be filtered out
+        self::assertCount(0, $classDescription->getDependencies());
+    }
+
+    public function test_it_should_not_filter_user_defined_classes_in_root_namespace(): void
+    {
+        $FQCN = 'MyClass';
+
+        $classDescription = (new ClassDescriptionBuilder())
+            ->setFilePath('src/Foo.php')
+            ->setClassName($FQCN)
+            ->addDependency(new ClassDependency('NonExistentUserClass', 10))
+            ->build();
+
+        self::assertInstanceOf(ClassDescription::class, $classDescription);
+
+        // User-defined classes in root namespace should NOT be filtered
+        self::assertCount(1, $classDescription->getDependencies());
+        self::assertEquals('NonExistentUserClass', $classDescription->getDependencies()[0]->getFQCN()->toString());
+    }
+
+    public function test_it_should_not_filter_user_defined_classes_with_namespace(): void
+    {
+        $FQCN = 'MyClass';
+
+        $classDescription = (new ClassDescriptionBuilder())
+            ->setFilePath('src/Foo.php')
+            ->setClassName($FQCN)
+            ->addDependency(new ClassDependency('Vendor\Package\SomeClass', 10))
+            ->addDependency(new ClassDependency('App\Domain\Entity', 15))
+            ->build();
+
+        self::assertInstanceOf(ClassDescription::class, $classDescription);
+
+        // User-defined classes with namespaces should not be filtered
+        self::assertCount(2, $classDescription->getDependencies());
+    }
+
+    public function test_it_should_filter_mixed_dependencies_correctly(): void
+    {
+        $FQCN = 'MyClass';
+
+        $classDescription = (new ClassDescriptionBuilder())
+            ->setFilePath('src/Foo.php')
+            ->setClassName($FQCN)
+            ->addDependency(new ClassDependency('DateTime', 10)) // PHP core - filtered
+            ->addDependency(new ClassDependency('Vendor\Package\SomeClass', 15)) // Namespaced - kept
+            ->addDependency(new ClassDependency('Exception', 20)) // PHP core - filtered
+            ->addDependency(new ClassDependency('NonExistentUserClass', 25)) // User root class - kept
+            ->addDependency(new ClassDependency('PDO', 30)) // PHP core - filtered
+            ->build();
+
+        self::assertInstanceOf(ClassDescription::class, $classDescription);
+
+        // Should keep only the 2 non-PHP-core dependencies
+        self::assertCount(2, $classDescription->getDependencies());
+
+        $dependencies = $classDescription->getDependencies();
+        self::assertEquals('Vendor\Package\SomeClass', $dependencies[0]->getFQCN()->toString());
+        self::assertEquals('NonExistentUserClass', $dependencies[1]->getFQCN()->toString());
+    }
+
+    public function test_it_should_filter_internal_classes_with_namespaces(): void
+    {
+        $FQCN = 'MyClass';
+
+        // ReflectionClass is a PHP internal class in the root namespace
+        // If other internal namespaced classes exist (e.g., MongoDB\Driver\Manager),
+        // they should also be filtered. We test with ReflectionClass which is always available.
+        $classDescription = (new ClassDescriptionBuilder())
+            ->setFilePath('src/Foo.php')
+            ->setClassName($FQCN)
+            ->addDependency(new ClassDependency('ReflectionClass', 10)) // Internal root - filtered
+            ->addDependency(new ClassDependency('App\MyClass', 15)) // User namespaced - kept
+            ->build();
+
+        self::assertInstanceOf(ClassDescription::class, $classDescription);
+
+        // ReflectionClass should be filtered, only App\MyClass should remain
+        self::assertCount(1, $classDescription->getDependencies());
+        self::assertEquals('App\MyClass', $classDescription->getDependencies()[0]->getFQCN()->toString());
+    }
 }
diff --git a/tests/Unit/Expressions/ForClasses/NotHaveDependencyOutsideNamespaceTest.php b/tests/Unit/Expressions/ForClasses/NotHaveDependencyOutsideNamespaceTest.php
index bcc3e0d5..aa729738 100644
--- a/tests/Unit/Expressions/ForClasses/NotHaveDependencyOutsideNamespaceTest.php
+++ b/tests/Unit/Expressions/ForClasses/NotHaveDependencyOutsideNamespaceTest.php
@@ -57,14 +57,13 @@ public function test_it_should_return_false_if_depends_on_namespace(): void
             ->setClassName('HappyIsland')
             ->addDependency(new ClassDependency('myNamespace', 100))
             ->addDependency(new ClassDependency('another\class', 200))
-            ->addDependency(new ClassDependency('\DateTime', 300))
             ->build();
 
         $because = 'we want to add this rule for our software';
         $violations = new Violations();
         $notHaveDependencyOutsideNamespace->evaluate($classDescription, $violations, $because);
 
-        self::assertEquals(2, $violations->count());
+        self::assertEquals(1, $violations->count());
     }
 
     public function test_it_should_not_return_violation_error_if_dependency_excluded(): void
@@ -84,20 +83,22 @@ public function test_it_should_not_return_violation_error_if_dependency_excluded
         self::assertEquals(0, $violations->count());
     }
 
-    public function test_it_should_not_return_violation_error_if_core_dependency_excluded(): void
+    public function test_it_should_automatically_exclude_php_core_classes(): void
     {
-        $notHaveDependencyOutsideNamespace = new NotHaveDependencyOutsideNamespace('myNamespace', [], true);
+        $notHaveDependencyOutsideNamespace = new NotHaveDependencyOutsideNamespace('myNamespace');
 
         $classDescription = (new ClassDescriptionBuilder())
             ->setFilePath('src/Foo.php')
             ->setClassName('HappyIsland')
-            ->addDependency(new ClassDependency('\DateTime', 100))
+            ->addDependency(new ClassDependency('another\class', 100))
             ->build();
 
         $because = 'we want to add this rule for our software';
         $violations = new Violations();
         $notHaveDependencyOutsideNamespace->evaluate($classDescription, $violations, $because);
 
-        self::assertEquals(0, $violations->count());
+        // PHP core classes are automatically filtered at the ClassDescriptionBuilder level
+        // So only 'another\class' should be reported as a violation
+        self::assertEquals(1, $violations->count());
     }
 }