> ## Documentation Index
> Fetch the complete documentation index at: https://docs.instructorphp.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Validation

## Overview

Instructor uses validation to verify if the response generated by LLM
meets the requirements of your response model. If the response does not
meet the requirements, Instructor will throw an exception.

Instructor uses Symfony's Validator component to validate the response,
check their documentation for more information on the usage:
[https://symfony.com/doc/current/components/validator.html](https://symfony.com/doc/current/components/validator.html)

Following example demonstrates how to use Symfony Validator's constraints
to validate the email field of response.

## Example

```php theme={null}
<?php
require 'examples/boot.php';

use Cognesy\Instructor\StructuredOutput;
use Cognesy\Instructor\Validation\Exceptions\ValidationException;
use Symfony\Component\Validator\Constraints as Assert;

class UserDetails
{
    public string $name;
    #[Assert\Email]
    #[Assert\NotBlank]
    /** Find user's email provided in the text or empty if it is missing */
    public ?string $email;
}

$caughtException = false;
$runtimeError = false;
try {
    $user = StructuredOutput::using('openai')
        ->withResponseClass(UserDetails::class)
        ->withMessages([['role' => 'user', 'content' => "you can reply to me via mail -- Jason"]])
        ->get();
} catch (ValidationException $e) {
    $caughtException = true;
    echo "Validation worked.\n";
} catch (Throwable $e) {
    // Provider/runtime failures are not validation behavior and should not fail the example.
    $runtimeError = true;
    echo "Validation failed with unexpected exception: {$e->getMessage()}\n";
}

if ($runtimeError) {
    echo "Skipping strict validation assertions due provider/runtime error.\n";
    return;
}

assert($caughtException === true);
assert(!isset($user));
?>
```