MetaSource is a performant source for RPM repositories metadata which has an access to the metadata of the different Fedora Linux package repositories and will serve you the most recent information available. It will parse through the "updates-testing" repository before moving onto the likes of "updates" and "releases" repository if no information is found in the previous repository.
Utilize the fast lookup interface to acquaint yourself with the API endpoints and expected outputs. Press ENTER after typing the name to execute a lookup in a new window. If you query for a non-existent branch - it will return an HTTP 400 error. If you query for a non-existent package - it will return an HTTP 404 error. Please report persistent HTTP 500 errors to the Fedora Infrastructure team.