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reCAPTCHA V2 – Callback-Based

Some websites implement reCAPTCHA V2 using a callback function instead of relying on the standard g-recaptcha-response field. In these cases, after solving the CAPTCHA successfully, you must invoke the site’s callback function with the token—rather than injecting it into a hidden field.

How to Identify a Callback Implementation​

Look for one of the following in the page source:

  • A data-callback="myFunction" attribute in the reCAPTCHA <div>: 
    <div class="g-recaptcha" data-sitekey="..." data-callback="SubmitToken"></div>
  • A callback property in a grecaptcha.render() call: 
    grecaptcha.render('recaptcha-container', {
      sitekey: '...',
      callback: userVerified
    });
  • The callback name stored in the global reCAPTCHA config (inspect via browser console): 
    ___grecaptcha_cfg.clients[0].aa.l.callback

    Note: The object path (e.g., aa.l) may vary—check clients[1], clients[2], etc.

Integration Workflow​

  1. Extract the site key and page URL (same as standard reCAPTCHA V2).

  2. Submit the task:

  1. Wait 15–20 seconds, then poll for the result:

  1. Upon receiving the token, call the site’s callback function directly:

    // Replace `SubmitToken` with the actual callback name
    SubmitToken("TOKEN_FROM_CAPTCHA_AI");

    This typically triggers form validation or automatic submission on the target site.

Important: Do not attempt to set g-recaptcha-response in callback-based implementations—it may be ignored or cause errors.

Best Practices​

  • Always verify the callback name in the live page context—minified or dynamically generated sites may use obfuscated names.
  • If the page uses multiple reCAPTCHAs, ensure you’re targeting the correct clients[N] index.
  • You can include browser-like context (user-agent, cookies, proxy) to mimic real-user conditions, which can improve solve success rates.