diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..e57a11e
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,4 @@
+/vendor/
+/.php-cs-fixer.cache
+/.phpunit.result.cache
+/composer.lock
diff --git a/extension-mocks.neon b/extension-mocks.neon
new file mode 100644
index 0000000..a172105
--- /dev/null
+++ b/extension-mocks.neon
@@ -0,0 +1,3 @@
+rules:
+    - Ibexa\PHPStan\Rules\RequireMockObjectInPropertyTypeRule
+    - Ibexa\PHPStan\Rules\RequireConcreteTypeForMockReturnRule
diff --git a/phpstan.neon b/phpstan.neon
index ab3d432..c6a905c 100644
--- a/phpstan.neon
+++ b/phpstan.neon
@@ -3,4 +3,6 @@ parameters:
     paths:
         - rules
         - tests
+    excludePaths:
+        - tests/rules/Fixtures/*
     checkMissingCallableSignature: true
diff --git a/rules/NoConfigResolverParametersInConstructorRule.php b/rules/NoConfigResolverParametersInConstructorRule.php
index 6bd3213..94fa6d8 100644
--- a/rules/NoConfigResolverParametersInConstructorRule.php
+++ b/rules/NoConfigResolverParametersInConstructorRule.php
@@ -60,7 +60,7 @@ public function processNode(Node $node, Scope $scope): array
         return [
             RuleErrorBuilder
                 ::message('Referring to ConfigResolver parameters in constructor is not allowed due to potential scope change.')
-                ->identifier('Ibexa.NoConfigResolverParametersInConstructor')
+                ->identifier('Ibexa.noConfigResolverParametersInConstructor')
                 ->nonIgnorable()
                 ->build(),
         ];
diff --git a/rules/RequireClosureReturnTypeRule.php b/rules/RequireClosureReturnTypeRule.php
index 5a9975e..ace2ca5 100644
--- a/rules/RequireClosureReturnTypeRule.php
+++ b/rules/RequireClosureReturnTypeRule.php
@@ -23,6 +23,9 @@ public function getNodeType(): string
         return Node\Expr::class;
     }
 
+    /**
+     * @return list<\PHPStan\Rules\IdentifierRuleError>
+     */
     public function processNode(Node $node, Scope $scope): array
     {
         if (!$node instanceof Node\Expr\Closure && !$node instanceof Node\Expr\ArrowFunction) {
@@ -35,7 +38,7 @@ public function processNode(Node $node, Scope $scope): array
             return [
                 RuleErrorBuilder::message(
                     sprintf('%s is missing a return type declaration', $nodeType)
-                )->build(),
+                )->identifier('Ibexa.requireClosureReturnType')->build(),
             ];
         }
 
diff --git a/rules/RequireConcreteTypeForMockReturnRule.php b/rules/RequireConcreteTypeForMockReturnRule.php
new file mode 100644
index 0000000..30332a0
--- /dev/null
+++ b/rules/RequireConcreteTypeForMockReturnRule.php
@@ -0,0 +1,170 @@
+<?php
+
+/**
+ * @copyright Copyright (C) Ibexa AS. All rights reserved.
+ * @license For full copyright and license information view LICENSE file distributed with this source code.
+ */
+declare(strict_types=1);
+
+namespace Ibexa\PHPStan\Rules;
+
+use PhpParser\Node;
+use PhpParser\Node\Expr\MethodCall;
+use PhpParser\Node\Expr\StaticCall;
+use PhpParser\Node\Expr\Variable;
+use PhpParser\Node\Identifier;
+use PhpParser\Node\IntersectionType;
+use PhpParser\Node\Name;
+use PhpParser\Node\NullableType;
+use PhpParser\Node\Stmt\ClassMethod;
+use PhpParser\Node\UnionType;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+
+/**
+ * @implements Rule<ClassMethod>
+ */
+final readonly class RequireConcreteTypeForMockReturnRule implements Rule
+{
+    public function getNodeType(): string
+    {
+        return ClassMethod::class;
+    }
+
+    /**
+     * @return list<\PHPStan\Rules\IdentifierRuleError>
+     */
+    public function processNode(Node $node, Scope $scope): array
+    {
+        if ($node->returnType === null || $node->stmts === null) {
+            return [];
+        }
+
+        if (!$this->returnsMock($node)) {
+            return [];
+        }
+
+        if (!$this->typeNodeIsMockObjectOnly($node->returnType)) {
+            return [];
+        }
+
+        return [
+            RuleErrorBuilder::message('Method returns a mock and declares only MockObject as return type. Use an intersection with a concrete type.')
+                ->identifier('Ibexa.requireConcreteTypeForMockReturn')
+                ->build(),
+        ];
+    }
+
+    private function returnsMock(ClassMethod $node): bool
+    {
+        $mockVariables = [];
+        foreach ($node->getStmts() ?? [] as $stmt) {
+            if ($stmt instanceof Node\Stmt\Expression && $stmt->expr instanceof Node\Expr\Assign) {
+                $assign = $stmt->expr;
+                if ($assign->var instanceof Variable && is_string($assign->var->name)) {
+                    if ($assign->expr instanceof MethodCall && $this->isCreateMockCall($assign->expr)) {
+                        $mockVariables[$assign->var->name] = true;
+                    }
+
+                    if ($assign->expr instanceof StaticCall && $this->isCreateMockCall($assign->expr)) {
+                        $mockVariables[$assign->var->name] = true;
+                    }
+                }
+            }
+
+            if (!$stmt instanceof Node\Stmt\Return_ || $stmt->expr === null) {
+                continue;
+            }
+
+            $expr = $stmt->expr;
+            if ($expr instanceof MethodCall && $this->isCreateMockCall($expr)) {
+                return true;
+            }
+
+            if ($expr instanceof StaticCall && $this->isCreateMockCall($expr)) {
+                return true;
+            }
+
+            if ($expr instanceof Variable && is_string($expr->name) && isset($mockVariables[$expr->name])) {
+                return true;
+            }
+        }
+
+        return false;
+    }
+
+    /**
+     * @param \PhpParser\Node\Expr\MethodCall|\PhpParser\Node\Expr\StaticCall $call
+     */
+    private function isCreateMockCall(Node $call): bool
+    {
+        if (!$call->name instanceof Node\Identifier) {
+            return false;
+        }
+
+        if ($call->name->toString() !== 'createMock') {
+            return false;
+        }
+
+        if ($call instanceof MethodCall) {
+            return $call->var instanceof Variable && $call->var->name === 'this';
+        }
+
+        return true;
+    }
+
+    private function typeNodeIsMockObjectOnly(Node $type): bool
+    {
+        if ($type instanceof NullableType) {
+            return $this->typeNodeIsMockObjectOnly($type->type);
+        }
+
+        if ($type instanceof IntersectionType) {
+            $hasMockObject = false;
+            foreach ($type->types as $innerType) {
+                if ($this->isMockObjectType($innerType)) {
+                    $hasMockObject = true;
+                    continue;
+                }
+
+                return false;
+            }
+
+            return $hasMockObject;
+        }
+
+        if ($type instanceof UnionType) {
+            $hasMockObject = false;
+            foreach ($type->types as $innerType) {
+                if ($innerType instanceof Name && $innerType->getLast() === 'null') {
+                    continue;
+                }
+
+                if ($this->isMockObjectType($innerType)) {
+                    $hasMockObject = true;
+                    continue;
+                }
+
+                return false;
+            }
+
+            return $hasMockObject;
+        }
+
+        return $this->isMockObjectType($type);
+    }
+
+    private function isMockObjectType(Node $type): bool
+    {
+        if ($type instanceof Identifier) {
+            return $type->toString() === 'MockObject';
+        }
+
+        if ($type instanceof Name) {
+            return $type->getLast() === 'MockObject';
+        }
+
+        return false;
+    }
+}
diff --git a/rules/RequireMockObjectInPropertyTypeRule.php b/rules/RequireMockObjectInPropertyTypeRule.php
new file mode 100644
index 0000000..15d7fd9
--- /dev/null
+++ b/rules/RequireMockObjectInPropertyTypeRule.php
@@ -0,0 +1,92 @@
+<?php
+
+/**
+ * @copyright Copyright (C) Ibexa AS. All rights reserved.
+ * @license For full copyright and license information view LICENSE file distributed with this source code.
+ */
+declare(strict_types=1);
+
+namespace Ibexa\PHPStan\Rules;
+
+use PhpParser\Node;
+use PhpParser\Node\Identifier;
+use PhpParser\Node\IntersectionType;
+use PhpParser\Node\Name;
+use PhpParser\Node\NullableType;
+use PhpParser\Node\Stmt\Property;
+use PhpParser\Node\UnionType;
+use PHPStan\Analyser\Scope;
+use PHPStan\Rules\Rule;
+use PHPStan\Rules\RuleErrorBuilder;
+
+/**
+ * @implements Rule<Property>
+ */
+final readonly class RequireMockObjectInPropertyTypeRule implements Rule
+{
+    public function getNodeType(): string
+    {
+        return Property::class;
+    }
+
+    /**
+     * @return list<\PHPStan\Rules\IdentifierRuleError>
+     */
+    public function processNode(Node $node, Scope $scope): array
+    {
+        if ($node->type === null) {
+            return [];
+        }
+
+        if (!$this->docCommentIncludesMockObject($node)) {
+            return [];
+        }
+
+        if ($this->typeNodeIncludesMockObject($node->type)) {
+            return [];
+        }
+
+        return [
+            RuleErrorBuilder::message('Property typed as MockObject only in PHPDoc. Use intersection type with MockObject.')
+                ->identifier('Ibexa.requireMockObjectPropertyType')
+                ->build(),
+        ];
+    }
+
+    private function typeNodeIncludesMockObject(Node $type): bool
+    {
+        if ($type instanceof NullableType) {
+            return $this->typeNodeIncludesMockObject($type->type);
+        }
+
+        if ($type instanceof UnionType || $type instanceof IntersectionType) {
+            foreach ($type->types as $innerType) {
+                if ($this->typeNodeIncludesMockObject($innerType)) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        if ($type instanceof Identifier) {
+            return $type->toString() === 'MockObject';
+        }
+
+        if ($type instanceof Name) {
+            return $type->getLast() === 'MockObject';
+        }
+
+        return false;
+    }
+
+    private function docCommentIncludesMockObject(Property $property): bool
+    {
+        $docComment = $property->getDocComment();
+        if ($docComment === null) {
+            return false;
+        }
+
+        return preg_match('/@var\\s+[^\\n]*MockObject/', $docComment->getText()) === 1;
+    }
+}
diff --git a/tests/rules/Fixtures/RequireConcreteTypeForMockReturnFixture.php b/tests/rules/Fixtures/RequireConcreteTypeForMockReturnFixture.php
new file mode 100644
index 0000000..784402b
--- /dev/null
+++ b/tests/rules/Fixtures/RequireConcreteTypeForMockReturnFixture.php
@@ -0,0 +1,39 @@
+<?php
+
+/**
+ * @copyright Copyright (C) Ibexa AS. All rights reserved.
+ * @license For full copyright and license information view LICENSE file distributed with this source code.
+ */
+declare(strict_types=1);
+
+namespace Ibexa\Tests\PHPStan\Rules\Fixtures;
+
+use PHPUnit\Framework\TestCase;
+
+final class ConcreteMockReturnTypeFixture extends TestCase
+{
+    private function createFoo(): Foo
+    {
+        $foo = $this->createMock(Foo::class);
+
+        return $foo;
+    }
+
+    private function createFooOk(): Foo&MockObject
+    {
+        return $this->createMock(Foo::class);
+    }
+
+    private function createMockObjectOnly(): MockObject
+    {
+        return $this->createMock(Foo::class);
+    }
+}
+
+final class Foo
+{
+}
+
+interface MockObject
+{
+}
diff --git a/tests/rules/Fixtures/RequireMockObjectInPropertyTypeFixture.php b/tests/rules/Fixtures/RequireMockObjectInPropertyTypeFixture.php
new file mode 100644
index 0000000..3708f8b
--- /dev/null
+++ b/tests/rules/Fixtures/RequireMockObjectInPropertyTypeFixture.php
@@ -0,0 +1,25 @@
+<?php
+
+/**
+ * @copyright Copyright (C) Ibexa AS. All rights reserved.
+ * @license For full copyright and license information view LICENSE file distributed with this source code.
+ */
+declare(strict_types=1);
+
+namespace Ibexa\Tests\PHPStan\Rules\Fixtures;
+
+use PHPUnit\Framework\TestCase;
+
+final class PropertyMockTypeTest extends TestCase
+{
+    /** @var Foo&MockObject */
+    private Foo $foo;
+}
+
+final class Foo
+{
+}
+
+interface MockObject
+{
+}
diff --git a/tests/rules/RequireConcreteTypeForMockReturnRuleTest.php b/tests/rules/RequireConcreteTypeForMockReturnRuleTest.php
new file mode 100644
index 0000000..02855e9
--- /dev/null
+++ b/tests/rules/RequireConcreteTypeForMockReturnRuleTest.php
@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * @copyright Copyright (C) Ibexa AS. All rights reserved.
+ * @license For full copyright and license information view LICENSE file distributed with this source code.
+ */
+declare(strict_types=1);
+
+namespace Ibexa\Tests\PHPStan\Rules;
+
+use Ibexa\PHPStan\Rules\RequireConcreteTypeForMockReturnRule;
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<RequireConcreteTypeForMockReturnRule>
+ */
+final class RequireConcreteTypeForMockReturnRuleTest extends RuleTestCase
+{
+    protected function getRule(): Rule
+    {
+        return new RequireConcreteTypeForMockReturnRule();
+    }
+
+    public function testRule(): void
+    {
+        $this->analyse(
+            [__DIR__ . '/Fixtures/RequireConcreteTypeForMockReturnFixture.php'],
+            [
+                [
+                    'Method returns a mock and declares only MockObject as return type. Use an intersection with a concrete type.',
+                    27,
+                ],
+            ]
+        );
+    }
+}
diff --git a/tests/rules/RequireMockObjectInPropertyTypeRuleTest.php b/tests/rules/RequireMockObjectInPropertyTypeRuleTest.php
new file mode 100644
index 0000000..55e97cb
--- /dev/null
+++ b/tests/rules/RequireMockObjectInPropertyTypeRuleTest.php
@@ -0,0 +1,37 @@
+<?php
+
+/**
+ * @copyright Copyright (C) Ibexa AS. All rights reserved.
+ * @license For full copyright and license information view LICENSE file distributed with this source code.
+ */
+declare(strict_types=1);
+
+namespace Ibexa\Tests\PHPStan\Rules;
+
+use Ibexa\PHPStan\Rules\RequireMockObjectInPropertyTypeRule;
+use PHPStan\Rules\Rule;
+use PHPStan\Testing\RuleTestCase;
+
+/**
+ * @extends RuleTestCase<RequireMockObjectInPropertyTypeRule>
+ */
+final class RequireMockObjectInPropertyTypeRuleTest extends RuleTestCase
+{
+    protected function getRule(): Rule
+    {
+        return new RequireMockObjectInPropertyTypeRule();
+    }
+
+    public function testRule(): void
+    {
+        $this->analyse(
+            [__DIR__ . '/Fixtures/RequireMockObjectInPropertyTypeFixture.php'],
+            [
+                [
+                    'Property typed as MockObject only in PHPDoc. Use intersection type with MockObject.',
+                    16,
+                ],
+            ]
+        );
+    }
+}