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Developer's Guide

Welcome to the reCAPTCHA developer documentation.

reCAPTCHA protects you against spam and other types of automated abuse. Here, we explain how to add reCAPTCHA to your site or application.


This documentation is designed for people familiar with HTML forms, server-side processing or mobile application development. To install reCAPTCHA, you will probably need to edit some code.

We hope you find this documentation easy to follow. Make sure to join the reCAPTCHA developer forum to give feedback and discuss the API.

You can find a reCAPTCHA codelab here.


To start using reCAPTCHA, you need to sign up for an API key pair for your site. The key pair consists of a site key and secret key. The site key is used to invoke reCAPTCHA service on your site or mobile application. The secret key authorizes communication between your application backend and the reCAPTCHA server to verify the user's response. The secret key needs to be kept safe for security purposes.

First, choose the type of reCAPTCHA and then fill in authorized domains or package names. After you accept our terms of service, you can click Register button to get new API key pair.

Now please take the following steps to add reCAPTCHA to your site or mobile application:

  1. Choose the client side integration:
  2. Verifying the user's response