The API and all data returned from it are licensed under a Creative Commons Attribution-NonCommercial 4.0 International License.
This means that the API and the questions it returns are free for noncommercial use. If you have somewhere suitable in your app, then please credit the API somewhere discreet - we love having our hard work shared!
If you would like to use the API commercially, this service is offered by a paid subscription.
If you are a school or college we can whitelist your IP to bypass the rate limit free of charge and will do our best to offer support, email email@example.com to find out more.