Validate the token

Learn how to securely validate Turnstile tokens on your server using the Siteverify API.

:::caution[Mandatory server-side validation]

You must call the Siteverify API to complete your Turnstile implementation. The client-side widget alone does not protect your forms.

Server-side validation is required because:

• Tokens can be forged. An attacker can submit any string to your form endpoint without completing a challenge.
• Tokens expire. Each token is valid for 300 seconds (5 minutes) after generation.
• Tokens are single-use. Each token can only be validated once. A replayed token will be rejected with the timeout-or-duplicate error code. :::

Process

1. Client generates token: Visitor completes Turnstile challenge on your webpage.
2. Token sent to server: Form submission includes the Turnstile token.
3. Server validates token: Your server calls Cloudflare's Siteverify API.
4. Cloudflare responds: Returns success or failure and additional data.
5. Server takes action: Allow or reject the original request based on validation.

Siteverify API overview

POST https://challenges.cloudflare.com/turnstile/v0/siteverify

Request format

The API accepts both application/x-www-form-urlencoded and application/json requests, but always returns JSON responses.

Required parameters

Token characteristics

• Maximum length: 2048 characters
• Validity period: 300 seconds (5 minutes) from generation
• Single use: Each token can only be validated once
• Automatic expiry: Tokens automatically expire and cannot be reused

The validation token issued by Turnstile is valid for five minutes. If a user submits the form after this period, the token is considered expired. In this scenario, the server-side verification API will return a failure, and the error-codes field in the response will include timeout-or-duplicate.

To ensure a successful validation, the visitor must initiate the request and submit the token to your backend within the five-minute window. Otherwise, the Turnstile widget needs to be refreshed to generate a new token. This can be done using the turnstile.reset function.

Basic validation examples

JavaScript

JSON

const SECRET_KEY = "your-secret-key";

async function validateTurnstile(token, remoteip) {
	try {
		const response = await fetch(
			"https://challenges.cloudflare.com/turnstile/v0/siteverify",
			{
				method: "POST",
				headers: {
					"Content-Type": "application/json",
				},
				body: JSON.stringify({
					secret: SECRET_KEY,
					response: token,
					remoteip: remoteip,
				}),
			},
		);

		const result = await response.json();
		return result;
	} catch (error) {
		console.error("Turnstile validation error:", error);
		return { success: false, "error-codes": ["internal-error"] };
	}
}

Form Data

const SECRET_KEY = "your-secret-key";

async function validateTurnstile(token, remoteip) {
	const formData = new FormData();
	formData.append("secret", SECRET_KEY);
	formData.append("response", token);
	formData.append("remoteip", remoteip);

	try {
		const response = await fetch(
			"https://challenges.cloudflare.com/turnstile/v0/siteverify",
			{
				method: "POST",
				body: formData,
			},
		);

		const result = await response.json();
		return result;
	} catch (error) {
		console.error("Turnstile validation error:", error);
		return { success: false, "error-codes": ["internal-error"] };
	}
}

// Usage in form handler
async function handleFormSubmission(request) {
	const body = await request.formData();
	const token = body.get("cf-turnstile-response");
	const ip =
		request.headers.get("CF-Connecting-IP") ||
		request.headers.get("X-Forwarded-For") ||
		"unknown";

	const validation = await validateTurnstile(token, ip);

	if (validation.success) {
		// Token is valid - process the form
		console.log("Valid submission from:", validation.hostname);
		return processForm(body);
	} else {
		// Token is invalid - reject the submission
		console.log("Invalid token:", validation["error-codes"]);
		return new Response("Invalid verification", { status: 400 });
	}
}

PHP

<?php
function validateTurnstile($token, $secret, $remoteip = null) {
    $url = 'https://challenges.cloudflare.com/turnstile/v0/siteverify';

    $data = [
        'secret' => $secret,
        'response' => $token
    ];

    if ($remoteip) {
        $data['remoteip'] = $remoteip;
    }

    $ch = curl_init($url);
    curl_setopt_array($ch, [
        CURLOPT_POST => true,
        CURLOPT_POSTFIELDS => http_build_query($data),
        CURLOPT_HTTPHEADER => ['Content-Type: application/x-www-form-urlencoded'],
        CURLOPT_RETURNTRANSFER => true,
        CURLOPT_CONNECTTIMEOUT => 5,
        CURLOPT_TIMEOUT => 10,
    ]);

    $response = curl_exec($ch);
    $error = curl_error($ch);
    curl_close($ch);

    if ($response === false || $error !== '') {
        return ['success' => false, 'error-codes' => ['internal-error']];
    }

    return json_decode($response, true);

}

// Usage
$secret_key = 'your-secret-key';
$token = $_POST['cf-turnstile-response'] ?? '';
$remoteip = $_SERVER['HTTP_CF_CONNECTING_IP'] ??
$_SERVER['HTTP_X_FORWARDED_FOR'] ??
$_SERVER['REMOTE_ADDR'];

$validation = validateTurnstile($token, $secret_key, $remoteip);

if ($validation['success']) {
// Valid token - process form
echo "Form submission successful!";
// Process your form data here
} else {
// Invalid token - show error
echo "Verification failed. Please try again.";
error_log('Turnstile validation failed: ' . implode(', ', $validation['error-codes']));
}
?>

Python

import requests

def validate_turnstile(token, secret, remoteip=None):
    url = 'https://challenges.cloudflare.com/turnstile/v0/siteverify'

    data = {
        'secret': secret,
        'response': token
    }

    if remoteip:
        data['remoteip'] = remoteip

    try:
        response = requests.post(url, data=data, timeout=10)
        response.raise_for_status()
        return response.json()
    except requests.RequestException as e:
        print(f"Turnstile validation error: {e}")
        return {'success': False, 'error-codes': ['internal-error']}

# Usage with Flask
from flask import Flask, request, jsonify

app = Flask(__name__)
SECRET_KEY = 'your-secret-key'

@app.route('/submit-form', methods=['POST'])
def submit_form():
    token = request.form.get('cf-turnstile-response')
    remoteip = request.headers.get('CF-Connecting-IP') or \
               request.headers.get('X-Forwarded-For') or \
               request.remote_addr

    validation = validate_turnstile(token, SECRET_KEY, remoteip)

    if validation['success']:
        # Valid token - process form
        return jsonify({'status': 'success', 'message': 'Form submitted successfully'})
    else:
        # Invalid token - reject submission
        return jsonify({
            'status': 'error',
            'message': 'Verification failed',
            'errors': validation['error-codes']
        }), 400

Java

import org.springframework.web.client.RestTemplate;
import org.springframework.util.LinkedMultiValueMap;
import org.springframework.util.MultiValueMap;
import org.springframework.http.HttpEntity;
import org.springframework.http.HttpHeaders;
import org.springframework.http.MediaType;
import org.springframework.http.ResponseEntity;

@Service
public class TurnstileService {
private static final String SITEVERIFY_URL = "https://challenges.cloudflare.com/turnstile/v0/siteverify";
private final String secretKey = "your-secret-key";
private final RestTemplate restTemplate = new RestTemplate();

    public TurnstileResponse validateToken(String token, String remoteip) {
        HttpHeaders headers = new HttpHeaders();
        headers.setContentType(MediaType.APPLICATION_FORM_URLENCODED);

        MultiValueMap<String, String> params = new LinkedMultiValueMap<>();
        params.add("secret", secretKey);
        params.add("response", token);
        if (remoteip != null) {
            params.add("remoteip", remoteip);
        }

        HttpEntity<MultiValueMap<String, String>> request = new HttpEntity<>(params, headers);

        try {
            ResponseEntity<TurnstileResponse> response = restTemplate.postForEntity(
                SITEVERIFY_URL, request, TurnstileResponse.class);
            return response.getBody();
        } catch (Exception e) {
            TurnstileResponse errorResponse = new TurnstileResponse();
            errorResponse.setSuccess(false);
            errorResponse.setErrorCodes(List.of("internal-error"));
            return errorResponse;
        }
    }

}

// Controller usage
@PostMapping("/submit-form")
public ResponseEntity<?> submitForm(
@RequestParam("cf-turnstile-response") String token,
HttpServletRequest request) {

    String remoteip = request.getHeader("CF-Connecting-IP");
    if (remoteip == null) {
        remoteip = request.getHeader("X-Forwarded-For");
    }
    if (remoteip == null) {
        remoteip = request.getRemoteAddr();
    }

    TurnstileResponse validation = turnstileService.validateToken(token, remoteip);

    if (validation.isSuccess()) {
        // Valid token - process form
        return ResponseEntity.ok("Form submitted successfully");
    } else {
        // Invalid token - reject submission
        return ResponseEntity.badRequest()
            .body("Verification failed: " + validation.getErrorCodes());
    }

}

C#

using System.Text.Json;

public class TurnstileService
{
    private readonly HttpClient _httpClient;
    private readonly string _secretKey = "your-secret-key";
    private const string SiteverifyUrl = "https://challenges.cloudflare.com/turnstile/v0/siteverify";

    public TurnstileService(HttpClient httpClient)
    {
        _httpClient = httpClient;
    }

    public async Task<TurnstileResponse> ValidateTokenAsync(string token, string remoteip = null)
    {
        var parameters = new Dictionary<string, string>
        {
            { "secret", _secretKey },
            { "response", token }
        };

        if (!string.IsNullOrEmpty(remoteip))
        {
            parameters.Add("remoteip", remoteip);
        }

        var postContent = new FormUrlEncodedContent(parameters);

        try
        {
            var response = await _httpClient.PostAsync(SiteverifyUrl, postContent);
            var stringContent = await response.Content.ReadAsStringAsync();

            return JsonSerializer.Deserialize<TurnstileResponse>(stringContent);
        }
        catch (Exception ex)
        {
            return new TurnstileResponse
            {
                Success = false,
                ErrorCodes = new[] { "internal-error" }
            };
        }
    }
}

// Controller usage
[HttpPost("submit-form")]
public async Task<IActionResult> SubmitForm([FromForm] string cfTurnstileResponse)
{
    var remoteip = HttpContext.Request.Headers["CF-Connecting-IP"].FirstOrDefault() ??
                   HttpContext.Request.Headers["X-Forwarded-For"].FirstOrDefault() ??
                   HttpContext.Connection.RemoteIpAddress?.ToString();

    var validation = await _turnstileService.ValidateTokenAsync(cfTurnstileResponse, remoteip);

    if (validation.Success)
    {
        // Valid token - process form
        return Ok("Form submitted successfully");
    }
    else
    {
        // Invalid token - reject submission
        return BadRequest($"Verification failed: {string.Join(", ", validation.ErrorCodes)}");
    }
}

Advanced validation techniques

const crypto = require("crypto");

async function validateWithRetry(token, remoteip, maxRetries = 3) {
	const idempotencyKey = crypto.randomUUID();

	for (let attempt = 1; attempt <= maxRetries; attempt++) {
		try {
			const formData = new FormData();
			formData.append("secret", SECRET_KEY);
			formData.append("response", token);
			formData.append("remoteip", remoteip);
			formData.append("idempotency_key", idempotencyKey);

			const response = await fetch(
				"https://challenges.cloudflare.com/turnstile/v0/siteverify",
				{
					method: "POST",
					body: formData,
				},
			);

			const result = await response.json();

			if (response.ok) {
				return result;
			}

			// If this is the last attempt, return the error
			if (attempt === maxRetries) {
				return result;
			}

			// Wait before retrying (exponential backoff)
			await new Promise((resolve) =>
				setTimeout(resolve, Math.pow(2, attempt) * 1000),
			);
		} catch (error) {
			if (attempt === maxRetries) {
				return { success: false, "error-codes": ["internal-error"] };
			}
		}
	}
}

async function validateTurnstileEnhanced(
	token,
	remoteip,
	expectedAction = null,
	expectedHostname = null,
) {
	const validation = await validateTurnstile(token, remoteip);

	if (!validation.success) {
		return {
			valid: false,
			reason: "turnstile_failed",
			errors: validation["error-codes"],
		};
	}

	// Check if action matches expected value (if specified)
	if (expectedAction && validation.action !== expectedAction) {
		return {
			valid: false,
			reason: "action_mismatch",
			expected: expectedAction,
			received: validation.action,
		};
	}

	// Check if hostname matches expected value (if specified)
	if (expectedHostname && validation.hostname !== expectedHostname) {
		return {
			valid: false,
			reason: "hostname_mismatch",
			expected: expectedHostname,
			received: validation.hostname,
		};
	}

	// Check token age (warn if older than 4 minutes)
	const challengeTime = new Date(validation.challenge_ts);
	const now = new Date();
	const ageMinutes = (now - challengeTime) / (1000 * 60);

	if (ageMinutes > 4) {
		console.warn(`Token is ${ageMinutes.toFixed(1)} minutes old`);
	}

	return {
		valid: true,
		data: validation,
		tokenAge: ageMinutes,
	};
}

// Usage
const result = await validateTurnstileEnhanced(
	token,
	remoteip,
	"login", // expected action
	"example.com", // expected hostname
);

if (result.valid) {
	// Process the request
	console.log("Validation successful:", result.data);
} else {
	// Handle validation failure
	console.log("Validation failed:", result.reason);
}

API response format

Successful response

{
  "success": true,
  "challenge_ts": "2022-02-28T15:14:30.096Z",
  "hostname": "example.com",
  "error-codes": [],
  "action": "login",
  "cdata": "sessionid-123456789",
  "metadata": {
    "ephemeral_id": "x:9f78e0ed210960d7693b167e"
  }
}

Failed response

{
  "success": false,
  "error-codes": ["invalid-input-response"]
}

Response fields

Error codes reference

Implementation

class TurnstileValidator {
	constructor(secretKey, timeout = 10000) {
		this.secretKey = secretKey;
		this.timeout = timeout;
	}

	async validate(token, remoteip, options = {}) {
		// Input validation
		if (!token || typeof token !== "string") {
			return { success: false, error: "Invalid token format" };
		}

		if (token.length > 2048) {
			return { success: false, error: "Token too long" };
		}

		// Prepare request
		const controller = new AbortController();
		const timeoutId = setTimeout(() => controller.abort(), this.timeout);

		try {
			const formData = new FormData();
			formData.append("secret", this.secretKey);
			formData.append("response", token);

			if (remoteip) {
				formData.append("remoteip", remoteip);
			}

			if (options.idempotencyKey) {
				formData.append("idempotency_key", options.idempotencyKey);
			}

			const response = await fetch(
				"https://challenges.cloudflare.com/turnstile/v0/siteverify",
				{
					method: "POST",
					body: formData,
					signal: controller.signal,
				},
			);

			const result = await response.json();

			// Additional validation
			if (result.success) {
				if (
					options.expectedAction &&
					result.action !== options.expectedAction
				) {
					return {
						success: false,
						error: "Action mismatch",
						expected: options.expectedAction,
						received: result.action,
					};
				}

				if (
					options.expectedHostname &&
					result.hostname !== options.expectedHostname
				) {
					return {
						success: false,
						error: "Hostname mismatch",
						expected: options.expectedHostname,
						received: result.hostname,
					};
				}
			}

			return result;
		} catch (error) {
			if (error.name === "AbortError") {
				return { success: false, error: "Validation timeout" };
			}

			console.error("Turnstile validation error:", error);
			return { success: false, error: "Internal error" };
		} finally {
			clearTimeout(timeoutId);
		}
	}
}

// Usage
const validator = new TurnstileValidator(process.env.TURNSTILE_SECRET_KEY);

const result = await validator.validate(token, remoteip, {
	expectedAction: "login",
	expectedHostname: "example.com",
});

if (result.success) {
	// Process the request
} else {
	// Handle failure
	console.log("Validation failed:", result.error);
}

Testing

Best practices

Security

• Store your secret keys securely. Use environment variables or secure key management.
• Validate the token on every request. Never trust client-side validation alone.
• Check additional fields. Validate the action and hostname when specified.
• Monitor for abuse and log failed validations and unusual patterns.
• Use HTTPS. Always validate over secure connections.
• Only call the Siteverify API in your backend environment. If you expose the secret key in the front-end client code to call Siteverify, attackers can bypass the security check. Ensure that your client-side code sends the validation token to your backend, and that your backend is the sole caller of the Siteverify API.

Performance

• Set reasonable timeouts. Do not wait indefinitely for Siteverify responses.
• Implement retry logic and handle temporary network issues.
• Cache validation results for the same token, if it is needed for your flow.
• Monitor your API latency. Track the Siteverify response time.

Error handling

• Have fallback behavior for API failures.
• Use user-friendly messaging. Do not expose internal error details to users.
• Properly log errors for debugging without exposing secrets.
• Rate limit to protect against validation flooding.