API Sandbox
You can use this form to make a request and I save you the trouble of testing with CURL or similar whether your API key works as expected. As long as the Sandbox post variable exists (currently you cannot change it on this page) then nothing will be written to the database.
On success the form will take you to an empty page with HTTP status code 200 and a predefined number 42 as the id of the made up game. The form will show a page with HTTP status code 403 when the API key is not valid.