diff --git a/src/Model/Fields/Field.php b/src/Model/Fields/Field.php
index d720c22..b50b5cd 100644
--- a/src/Model/Fields/Field.php
+++ b/src/Model/Fields/Field.php
@@ -36,12 +36,16 @@ class Field implements FieldTypes
     /** @var FieldValidator */
     protected $FieldValidator;
 
+    /** @var array<callable> */
+    protected $customValidators = [];
+
     /** @var array<string> */
     private $errors = [];
 
     public function __construct()
     {
         $this->FieldValidator = new FieldValidator();
+        $this->initValidators();
     }
 
     public function getValue()
@@ -61,6 +65,11 @@ public function getName()
         return $this->name;
     }
 
+    public function addValidator(callable $callback)
+    {
+        $this->customValidators[] = $callback;
+    }
+
     public function setValue($value)
     {
         $this->checkMaximum($value);
@@ -70,6 +79,9 @@ public function setValue($value)
         if (!is_null($value)) {
             $this->checkValue($value);
         }
+        if (!empty($this->customValidators)) {
+            $this->checkCustomValidators($value);
+        }
         if (!empty($this->errors)) {
             throw new InvalidArgumentException(print_r($this->errors, true));
         }
@@ -136,4 +148,27 @@ public function checkValue($value)
             );
         }
     }
+
+    protected function initValidators() {}
+
+    private function checkCustomValidators($value)
+    {
+        foreach ($this->customValidators as $validator) {
+            $result = $validator($value, $this);
+
+            if (!$result instanceof FieldValidationResultInterface) {
+                throw new InvalidArgumentException(
+                    'Custom validator must return an instance of FieldValidationResultInterface.'
+                );
+            }
+
+            if (!$result->isValid()) {
+                $this->errors[] = sprintf(
+                    'Validation failed for field %s: %s',
+                    $this->name,
+                    (string) $result->getMessage()
+                );
+            }
+        }
+    }
 }
diff --git a/src/Model/Fields/FieldValidationResult.php b/src/Model/Fields/FieldValidationResult.php
new file mode 100644
index 0000000..acd3906
--- /dev/null
+++ b/src/Model/Fields/FieldValidationResult.php
@@ -0,0 +1,30 @@
+<?php
+
+namespace Tpay\OpenApi\Model\Fields;
+
+class FieldValidationResult implements FieldValidationResultInterface
+{
+    /** @var bool */
+    private $valid;
+
+    /** @var null|string */
+    private $message;
+
+    public function __construct($valid, $message = null)
+    {
+        $this->valid = $valid;
+        $this->message = $message;
+    }
+
+    /** @return bool */
+    public function isValid()
+    {
+        return $this->valid;
+    }
+
+    /** @return null|string */
+    public function getMessage()
+    {
+        return $this->message;
+    }
+}
diff --git a/src/Model/Fields/FieldValidationResultInterface.php b/src/Model/Fields/FieldValidationResultInterface.php
new file mode 100644
index 0000000..ae5321c
--- /dev/null
+++ b/src/Model/Fields/FieldValidationResultInterface.php
@@ -0,0 +1,12 @@
+<?php
+
+namespace Tpay\OpenApi\Model\Fields;
+
+interface FieldValidationResultInterface
+{
+    /** @return bool */
+    public function isValid();
+
+    /** @return null|string */
+    public function getMessage();
+}
diff --git a/src/Model/Fields/FieldValidator.php b/src/Model/Fields/FieldValidator.php
index 4fa24e4..36675b7 100644
--- a/src/Model/Fields/FieldValidator.php
+++ b/src/Model/Fields/FieldValidator.php
@@ -12,7 +12,7 @@ class FieldValidator implements FieldTypes
      */
     public function isTooLong($maxLength, $value)
     {
-        return (bool) (strlen($value) > $maxLength);
+        return (bool) (strlen((string) $value) > $maxLength);
     }
 
     /**
@@ -23,7 +23,7 @@ public function isTooLong($maxLength, $value)
      */
     public function isTooShort($minLength, $value)
     {
-        return (bool) (strlen($value) < $minLength);
+        return (bool) (strlen((string) $value) < $minLength);
     }
 
     /**
diff --git a/src/Model/Fields/Payer/IP.php b/src/Model/Fields/Payer/IP.php
index 2b5e81a..eab1e0f 100644
--- a/src/Model/Fields/Payer/IP.php
+++ b/src/Model/Fields/Payer/IP.php
@@ -3,6 +3,7 @@
 namespace Tpay\OpenApi\Model\Fields\Payer;
 
 use Tpay\OpenApi\Model\Fields\Field;
+use Tpay\OpenApi\Model\Fields\FieldValidationResult;
 
 /**
  * @method getValue(): string
@@ -13,5 +14,15 @@ class IP extends Field
     protected $type = self::STRING;
     protected $minLength = 3;
     protected $maxLength = 255;
-    protected $pattern = '^([0-9]{1,3}\.){3}[0-9]{1,3}$';
+
+    protected function initValidators()
+    {
+        $this->addValidator(function ($value) {
+            if (false === filter_var($value, FILTER_VALIDATE_IP)) {
+                return new FieldValidationResult(false, 'Invalid IP address.');
+            }
+
+            return new FieldValidationResult(true);
+        });
+    }
 }
diff --git a/tests/Model/Fields/Payer/IpTest.php b/tests/Model/Fields/Payer/IpTest.php
new file mode 100644
index 0000000..e36f3db
--- /dev/null
+++ b/tests/Model/Fields/Payer/IpTest.php
@@ -0,0 +1,58 @@
+<?php
+
+namespace Model\Fields\Payer;
+
+use InvalidArgumentException;
+use PHPUnit\Framework\TestCase;
+use Tpay\OpenApi\Model\Fields\Payer\IP;
+
+class IpTest extends TestCase
+{
+    public function testIpv4()
+    {
+        $ip = new Ip();
+        $ip->setValue('127.0.0.1');
+
+        $this->assertEquals('127.0.0.1', $ip->getValue());
+    }
+
+    public function testIpv6()
+    {
+        $ip = new Ip();
+        $ip->setValue('2001:db8::1');
+
+        $this->assertEquals('2001:db8::1', $ip->getValue());
+    }
+
+    public function testInvalidIp()
+    {
+        $ip = new Ip();
+
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Validation failed for field Tpay\OpenApi\Model\Fields\Payer\IP: Invalid IP address.');
+
+        $ip->setValue('TEST123');
+    }
+
+    public function testNull()
+    {
+        $ip = new Ip();
+
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Value of field Tpay\OpenApi\Model\Fields\Payer\IP is too short. Min required 3');
+        $this->expectExceptionMessage('Validation failed for field Tpay\OpenApi\Model\Fields\Payer\IP: Invalid IP address.');
+
+        $ip->setValue(null);
+    }
+
+    public function testWrongType()
+    {
+        $ip = new Ip();
+
+        $this->expectException(InvalidArgumentException::class);
+        $this->expectExceptionMessage('Value type of field Tpay\OpenApi\Model\Fields\Payer\IP is invalid. Should be string type');
+        $this->expectExceptionMessage('Validation failed for field Tpay\OpenApi\Model\Fields\Payer\IP: Invalid IP address.');
+
+        $ip->setValue(123212312321);
+    }
+}
diff --git a/tests/Model/ModelsTest.php b/tests/Model/ModelsTest.php
index 9d5274f..193d383 100644
--- a/tests/Model/ModelsTest.php
+++ b/tests/Model/ModelsTest.php
@@ -6,6 +6,7 @@
 use RecursiveDirectoryIterator;
 use RecursiveIteratorIterator;
 use SplFileInfo;
+use Tpay\OpenApi\Model\Fields\FieldValidationResult;
 
 class ModelsTest extends TestCase
 {
@@ -42,6 +43,10 @@ public static function dataModel()
             );
             $className = str_replace('/', '\\', $className);
 
+            if (FieldValidationResult::class === $className) {
+                continue;
+            }
+
             yield $className => [$className];
         }
     }