If you are answering a challenge in PPCG tagged [stack-exchange-api], you have probably exceeded your API limit by now. This app allows you to use a higher limit by using the app tokens provided:
Pass this as
key in the URL to achieve a higher rate limit!
Not sure why you would need this, but pass this is as
client_id in the URL if needed.
This app cannot be used for auth.
Don't worry, I'm not revealing any secrets. The documentation says that key and client id "is not secret, and may be safely embeded in distributed binaries."