diff --git a/README.md b/README.md
index 282e69e..b44b6d0 100644
--- a/README.md
+++ b/README.md
@@ -95,6 +95,7 @@ These are the available attributes and their corresponding PHPDoc annotations:
 
 | Attribute                                                                                                         | PHPDoc Annotations                   |
 |-------------------------------------------------------------------------------------------------------------------|--------------------------------------|
+| [Assert](https://github.com/php-static-analysis/attributes/blob/main/doc/Assert.md)                               | `@assert`                            |
 | [DefineType](https://github.com/php-static-analysis/attributes/blob/main/doc/DefineType.md)                       | `@type`                              |
 | [Deprecated](https://github.com/php-static-analysis/attributes/blob/main/doc/Deprecated.md)                       | `@deprecated`                        |
 | [Immmutable](https://github.com/php-static-analysis/attributes/blob/main/doc/Immmutable.md)                       | `@immmutable`                        |
diff --git a/composer.json b/composer.json
index 512bbfc..6d53369 100644
--- a/composer.json
+++ b/composer.json
@@ -24,9 +24,10 @@
     "prefer-stable": true,
     "require": {
         "php": ">=8.0",
-        "php-static-analysis/attributes": "^0.3.0 || dev-main",
-        "php-static-analysis/node-visitor": "^0.3.0 || dev-main",
-        "phpstan/phpstan": "^1.8"
+        "php-static-analysis/attributes": "^0.3.1 || dev-main",
+        "php-static-analysis/node-visitor": "^0.3.1 || dev-main",
+        "phpstan/phpstan": "^1.8",
+        "webmozart/assert": "^1.11"
     },
     "require-dev": {
         "php-static-analysis/psalm-plugin": "dev-main",
diff --git a/src/Parser/AttributeParser.php b/src/Parser/AttributeParser.php
index 82e2ec4..75be956 100644
--- a/src/Parser/AttributeParser.php
+++ b/src/Parser/AttributeParser.php
@@ -10,6 +10,7 @@
 use PhpStaticAnalysis\Attributes\Param;
 use PhpStaticAnalysis\Attributes\Returns;
 use PhpStaticAnalysis\NodeVisitor\AttributeNodeVisitor;
+use Webmozart\Assert\Assert;
 
 class AttributeParser implements Parser
 {
@@ -39,7 +40,7 @@ private function traverseAst(array $ast): array
         $traverser->addVisitor($nodeVisitor);
 
         $ast = $traverser->traverse($ast);
-        /** @var Stmt[] $ast */
+        Assert::allIsInstanceOf($ast, Stmt::class);
         return $ast;
     }
 }
diff --git a/tests/AssertAttributeTest.php b/tests/AssertAttributeTest.php
new file mode 100644
index 0000000..724216c
--- /dev/null
+++ b/tests/AssertAttributeTest.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension;
+
+class AssertAttributeTest extends BaseAttributeTestCase
+{
+    public function testMethodAssertAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/Assert/MethodAssertAttribute.php');
+        $this->assertCount(0, $errors);
+    }
+
+    public function testFunctionAssertAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/Assert/FunctionAssertAttribute.php');
+        $this->assertCount(0, $errors);
+    }
+
+    public function testInvalidMethodAssertAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/Assert/InvalidMethodAssertAttribute.php');
+
+        $expectedErrors = [
+            'Parameter #1 ...$params of attribute class PhpStaticAnalysis\Attributes\Assert constructor expects string, int given.' => 9,
+            'Attribute class PhpStaticAnalysis\Attributes\Assert does not have the property target.' => 14,
+        ];
+
+        $this->checkExpectedErrors($errors, $expectedErrors);
+    }
+}
diff --git a/tests/AssertIfFalseAttributeTest.php b/tests/AssertIfFalseAttributeTest.php
new file mode 100644
index 0000000..387a94e
--- /dev/null
+++ b/tests/AssertIfFalseAttributeTest.php
@@ -0,0 +1,31 @@
+<?php
+
+
+use test\PhpStaticAnalysis\PHPStanExtension\BaseAttributeTestCase;
+
+class AssertIfFalseAttributeTest extends BaseAttributeTestCase
+{
+    public function testMethodAssertIfFalseAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/AssertIfFalse/MethodAssertIfFalseAttribute.php');
+        $this->assertCount(0, $errors);
+    }
+
+    public function testFunctionAssertIfFalseAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/AssertIfFalse/FunctionAssertIfFalseAttribute.php');
+        $this->assertCount(0, $errors);
+    }
+
+    public function testInvalidMethodAssertIfFalseAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/AssertIfFalse/InvalidMethodAssertIfFalseAttribute.php');
+
+        $expectedErrors = [
+            'Parameter #1 ...$params of attribute class PhpStaticAnalysis\Attributes\AssertIfFalse constructor expects string, int given.' => 9,
+            'Attribute class PhpStaticAnalysis\Attributes\AssertIfFalse does not have the property target.' => 15,
+        ];
+
+        $this->checkExpectedErrors($errors, $expectedErrors);
+    }
+}
diff --git a/tests/AssertIfTrueAttributeTest.php b/tests/AssertIfTrueAttributeTest.php
new file mode 100644
index 0000000..16bee61
--- /dev/null
+++ b/tests/AssertIfTrueAttributeTest.php
@@ -0,0 +1,31 @@
+<?php
+
+
+use test\PhpStaticAnalysis\PHPStanExtension\BaseAttributeTestCase;
+
+class AssertIfTrueAttributeTest extends BaseAttributeTestCase
+{
+    public function testMethodAssertIfTrueAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/AssertIfTrue/MethodAssertIfTrueAttribute.php');
+        $this->assertCount(0, $errors);
+    }
+
+    public function testFunctionAssertIfTrueAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/AssertIfTrue/FunctionAssertIfTrueAttribute.php');
+        $this->assertCount(0, $errors);
+    }
+
+    public function testInvalidMethodAssertIfTrueAttribute(): void
+    {
+        $errors = $this->analyse(__DIR__ . '/data/AssertIfTrue/InvalidMethodAssertIfTrueAttribute.php');
+
+        $expectedErrors = [
+            'Parameter #1 ...$params of attribute class PhpStaticAnalysis\Attributes\AssertIfTrue constructor expects string, int given.' => 9,
+            'Attribute class PhpStaticAnalysis\Attributes\AssertIfTrue does not have the property target.' => 15,
+        ];
+
+        $this->checkExpectedErrors($errors, $expectedErrors);
+    }
+}
diff --git a/tests/data/Assert/FunctionAssertAttribute.php b/tests/data/Assert/FunctionAssertAttribute.php
new file mode 100644
index 0000000..6c7d8f5
--- /dev/null
+++ b/tests/data/Assert/FunctionAssertAttribute.php
@@ -0,0 +1,14 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\Assert;
+
+use Exception;
+use PhpStaticAnalysis\Attributes\Assert;
+
+#[Assert(name: 'string')]
+function checkString(mixed $name): void
+{
+    if (!is_string($name)) {
+        throw new Exception();
+    }
+}
diff --git a/tests/data/Assert/InvalidMethodAssertAttribute.php b/tests/data/Assert/InvalidMethodAssertAttribute.php
new file mode 100644
index 0000000..d46c0fe
--- /dev/null
+++ b/tests/data/Assert/InvalidMethodAssertAttribute.php
@@ -0,0 +1,16 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\Assert;
+
+use PhpStaticAnalysis\Attributes\Assert;
+
+class InvalidMethodAssertAttribute
+{
+    #[Assert(0)]
+    public function checkString(mixed $name): void
+    {
+    }
+
+    #[Assert(property: 'string')]
+    public string $property;
+}
diff --git a/tests/data/Assert/MethodAssertAttribute.php b/tests/data/Assert/MethodAssertAttribute.php
new file mode 100644
index 0000000..90f5329
--- /dev/null
+++ b/tests/data/Assert/MethodAssertAttribute.php
@@ -0,0 +1,114 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\Assert;
+
+use Exception;
+use PhpStaticAnalysis\Attributes\Assert;
+
+class MethodAssertAttribute
+{
+    #[Assert(name: 'string')] // checks name is string
+    public function checkString(mixed $name): void
+    {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    #[Assert(exception: Exception::class)]
+    public function checkException(mixed $exception): void
+    {
+        if (!$exception instanceof Exception) {
+            throw new Exception();
+        }
+    }
+
+    #[Assert('string $name')]
+    public function checkOtherString(mixed $name): void
+    {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    /**
+     * @deprecated
+     */
+    #[Assert(name: 'string')]
+    public function checkAnotherString(mixed $name): void
+    {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    /**
+     * @assert int $name
+     */
+    #[Assert(name: 'string')]
+    public function checkEvenMoreString(mixed $name): void
+    {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    #[Assert(
+        name1: 'string',
+        name2: 'string'
+    )]
+    public function checkStrings(mixed $name1, mixed $name2): void
+    {
+        if (!is_string($name1) || !is_string($name2)) {
+            throw new Exception();
+        }
+    }
+
+    #[Assert(name1: 'string')]
+    #[Assert(name2: 'string')]
+    public function checkOtherStrings(mixed $name1, mixed $name2): void
+    {
+        if (!is_string($name1) || !is_string($name2)) {
+            throw new Exception();
+        }
+    }
+
+    /**
+     * @assert string $name
+     */
+    public function checkMoreAndMoreString(mixed $name): void
+    {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    public function checkStringInParam(
+        #[Assert('string')]
+        mixed $name
+    ): void {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    public function checkStringInParamWithName(
+        #[Assert(name: 'string')]
+        mixed $name
+    ): void {
+        if (!is_string($name)) {
+            throw new Exception();
+        }
+    }
+
+    public function checkStringInTwoParams(
+        #[Assert('string')]
+        mixed $name1,
+        #[Assert('string')]
+        mixed $name2
+    ): void {
+        if (!is_string($name1) || !is_string($name2)) {
+            throw new Exception();
+        }
+    }
+}
diff --git a/tests/data/AssertIfFalse/FunctionAssertIfFalseAttribute.php b/tests/data/AssertIfFalse/FunctionAssertIfFalseAttribute.php
new file mode 100644
index 0000000..c15837d
--- /dev/null
+++ b/tests/data/AssertIfFalse/FunctionAssertIfFalseAttribute.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\AssertIfFalse;
+
+use Exception;
+use PhpStaticAnalysis\Attributes\AssertIfFalse;
+
+#[AssertIfFalse(name: 'string')]
+function checkString(mixed $name): bool
+{
+    return !is_string($name);
+}
diff --git a/tests/data/AssertIfFalse/InvalidMethodAssertIfFalseAttribute.php b/tests/data/AssertIfFalse/InvalidMethodAssertIfFalseAttribute.php
new file mode 100644
index 0000000..636bdea
--- /dev/null
+++ b/tests/data/AssertIfFalse/InvalidMethodAssertIfFalseAttribute.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\AssertIfFalse;
+
+use PhpStaticAnalysis\Attributes\AssertIfFalse;
+
+class InvalidMethodAssertIfFalseAttribute
+{
+    #[AssertIfFalse(0)]
+    public function checkString(mixed $name): bool
+    {
+        return false;
+    }
+
+    #[AssertIfFalse(property: 'string')]
+    public string $property;
+}
diff --git a/tests/data/AssertIfFalse/MethodAssertIfFalseAttribute.php b/tests/data/AssertIfFalse/MethodAssertIfFalseAttribute.php
new file mode 100644
index 0000000..cd2eddb
--- /dev/null
+++ b/tests/data/AssertIfFalse/MethodAssertIfFalseAttribute.php
@@ -0,0 +1,98 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\AssertIfFalse;
+
+use Exception;
+use PhpStaticAnalysis\Attributes\AssertIfFalse;
+
+class MethodAssertIfFalseAttribute
+{
+    #[AssertIfFalse(name: 'string')] // checks name is string
+    public function checkString(mixed $name): bool
+    {
+        return !is_string($name);
+    }
+
+    #[AssertIfFalse(exception: Exception::class)]
+    public function checkException(mixed $exception): bool
+    {
+        return !$exception instanceof Exception;
+    }
+
+    #[AssertIfFalse('string $name')]
+    public function checkOtherString(mixed $name): bool
+    {
+        return !is_string($name);
+    }
+
+    #[AssertIfFalse('string $this->name')]
+    public function checkOtherPropertyString(mixed $name): bool
+    {
+        return !is_string($name);
+    }
+
+    /**
+     * @deprecated
+     */
+    #[AssertIfFalse(name: 'string')]
+    public function checkAnotherString(mixed $name): bool
+    {
+        return !is_string($name);
+    }
+
+    /**
+     * @assert int $name
+     */
+    #[AssertIfFalse(name: 'string')]
+    public function checkEvenMoreString(mixed $name): bool
+    {
+        return !is_string($name);
+    }
+
+    #[AssertIfFalse(
+        name1: 'string',
+        name2: 'string'
+    )]
+    public function checkStrings(mixed $name1, mixed $name2): bool
+    {
+        return !is_string($name1) || !is_string($name2);
+    }
+
+    #[AssertIfFalse(name1: 'string')]
+    #[AssertIfFalse(name2: 'string')]
+    public function checkOtherStrings(mixed $name1, mixed $name2): bool
+    {
+        return !is_string($name1) || !is_string($name2);
+    }
+
+    /**
+     * @assert string $name
+     */
+    public function checkMoreAndMoreString(mixed $name): bool
+    {
+        return !is_string($name);
+    }
+
+    public function checkStringInParam(
+        #[AssertIfFalse('string')]
+        mixed $name
+    ): bool {
+        return !is_string($name);
+    }
+
+    public function checkStringInParamWithName(
+        #[AssertIfFalse(name: 'string')]
+        mixed $name
+    ): bool {
+        return !is_string($name);
+    }
+
+    public function checkStringInTwoParams(
+        #[AssertIfFalse('string')]
+        mixed $name1,
+        #[AssertIfFalse('string')]
+        mixed $name2
+    ): bool {
+        return !is_string($name1) || !is_string($name2);
+    }
+}
diff --git a/tests/data/AssertIfTrue/FunctionAssertIfTrueAttribute.php b/tests/data/AssertIfTrue/FunctionAssertIfTrueAttribute.php
new file mode 100644
index 0000000..ce0d939
--- /dev/null
+++ b/tests/data/AssertIfTrue/FunctionAssertIfTrueAttribute.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\AssertIfTrue;
+
+use Exception;
+use PhpStaticAnalysis\Attributes\AssertIfTrue;
+
+#[AssertIfTrue(name: 'string')]
+function checkString(mixed $name): bool
+{
+    return is_string($name);
+}
diff --git a/tests/data/AssertIfTrue/InvalidMethodAssertIfTrueAttribute.php b/tests/data/AssertIfTrue/InvalidMethodAssertIfTrueAttribute.php
new file mode 100644
index 0000000..0d50195
--- /dev/null
+++ b/tests/data/AssertIfTrue/InvalidMethodAssertIfTrueAttribute.php
@@ -0,0 +1,17 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\AssertIfTrue;
+
+use PhpStaticAnalysis\Attributes\AssertIfTrue;
+
+class InvalidMethodAssertIfTrueAttribute
+{
+    #[AssertIfTrue(0)]
+    public function checkString(mixed $name): bool
+    {
+        return true;
+    }
+
+    #[AssertIfTrue(property: 'string')]
+    public string $property;
+}
diff --git a/tests/data/AssertIfTrue/MethodAssertIfTrueAttribute.php b/tests/data/AssertIfTrue/MethodAssertIfTrueAttribute.php
new file mode 100644
index 0000000..88d736a
--- /dev/null
+++ b/tests/data/AssertIfTrue/MethodAssertIfTrueAttribute.php
@@ -0,0 +1,98 @@
+<?php
+
+namespace test\PhpStaticAnalysis\PHPStanExtension\data\AssertIfTrue;
+
+use Exception;
+use PhpStaticAnalysis\Attributes\AssertIfTrue;
+
+class MethodAssertIfTrueAttribute
+{
+    #[AssertIfTrue(name: 'string')] // checks name is string
+    public function checkString(mixed $name): bool
+    {
+        return is_string($name);
+    }
+
+    #[AssertIfTrue(exception: Exception::class)]
+    public function checkException(mixed $exception): bool
+    {
+        return $exception instanceof Exception;
+    }
+
+    #[AssertIfTrue('string $name')]
+    public function checkOtherString(mixed $name): bool
+    {
+        return is_string($name);
+    }
+
+    #[AssertIfTrue('string $this->name')]
+    public function checkOtherPropertyString(mixed $name): bool
+    {
+        return is_string($name);
+    }
+
+    /**
+     * @deprecated
+     */
+    #[AssertIfTrue(name: 'string')]
+    public function checkAnotherString(mixed $name): bool
+    {
+        return is_string($name);
+    }
+
+    /**
+     * @assert int $name
+     */
+    #[AssertIfTrue(name: 'string')]
+    public function checkEvenMoreString(mixed $name): bool
+    {
+        return is_string($name);
+    }
+
+    #[AssertIfTrue(
+        name1: 'string',
+        name2: 'string'
+    )]
+    public function checkStrings(mixed $name1, mixed $name2): bool
+    {
+        return is_string($name1) && is_string($name2);
+    }
+
+    #[AssertIfTrue(name1: 'string')]
+    #[AssertIfTrue(name2: 'string')]
+    public function checkOtherStrings(mixed $name1, mixed $name2): bool
+    {
+        return is_string($name1) && is_string($name2);
+    }
+
+    /**
+     * @assert string $name
+     */
+    public function checkMoreAndMoreString(mixed $name): bool
+    {
+        return is_string($name);
+    }
+
+    public function checkStringInParam(
+        #[AssertIfTrue('string')]
+        mixed $name
+    ): bool {
+        return is_string($name);
+    }
+
+    public function checkStringInParamWithName(
+        #[AssertIfTrue(name: 'string')]
+        mixed $name
+    ): bool {
+        return is_string($name);
+    }
+
+    public function checkStringInTwoParams(
+        #[AssertIfTrue('string')]
+        mixed $name1,
+        #[AssertIfTrue('string')]
+        mixed $name2
+    ): bool {
+        return is_string($name1) && is_string($name2);
+    }
+}