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Verifying the user's response

This page explains how to verify a user's response to a reCAPTCHA challenge from your application's backend.

For web users, you can get the user’s response token in one of three ways:

  • g-recaptcha-response POST parameter when the user submits the form on your site
  • grecaptcha.getResponse(opt_widget_id) after the user completes the reCAPTCHA challenge
  • As a string argument to your callback function if data-callback is specified in either the g-recaptcha tag attribute or the callback parameter in the grecaptcha.render method

For Android library users, you can call the SafetyNetApi.RecaptchaTokenResult.getTokenResult() method to get response token if the status returns successful.

Token Restrictions

Each reCAPTCHA user response token is valid for two minutes, and can only be verified once to prevent replay attacks. If you need a new token, you can re-run the reCAPTCHA verification.

After you get the response token, you need to verify it within two minutes with reCAPTCHA using the following API to ensure the token is valid.

API Request

URL: https://www.google.com/recaptcha/api/siteverify METHOD: POST

POST Parameter Description
secret Required. The shared key between your site and reCAPTCHA.
response Required. The user response token provided by the reCAPTCHA client-side integration on your site.
remoteip Optional. The user's IP address.

API Response

The response is a JSON object:

{
  "success": true|false,
  "challenge_ts": timestamp,  // timestamp of the challenge load (ISO format yyyy-MM-dd'T'HH:mm:ssZZ)
  "hostname": string,         // the hostname of the site where the reCAPTCHA was solved
  "error-codes": [...]        // optional
}

For reCAPTCHA Android:

{
  "success": true|false,
  "challenge_ts": timestamp,  // timestamp of the challenge load (ISO format yyyy-MM-dd'T'HH:mm:ssZZ)
  "apk_package_name": string, // the package name of the app where the reCAPTCHA was solved
  "error-codes": [...]        // optional
}

Error code reference

Error code Description
missing-input-secret The secret parameter is missing.
invalid-input-secret The secret parameter is invalid or malformed.
missing-input-response The response parameter is missing.
invalid-input-response The response parameter is invalid or malformed.
bad-request The request is invalid or malformed.
timeout-or-duplicate The response is no longer valid: either is too old or has been used previously.