To use the API, you must sign up for a Google AJAX Search API key, which you’ll include in the URL with which you access the API. We’ll use that key to track API usage.
The key you receive in the signup process is valid for a directory, and any subdirectories below that directory, on your website. If you sign up for the directory http://www.mygooglesearchsite.com/mysite, your key is valid for these URLs:
The key will not be valid for these URLs: