Can I get response data in xml or other formats?
Yes, just append format=xml to the url. This also works for format=pickle to return serialized python objects. Please note that JSON is the only format that is thoroughly tested, and a few calls (such as add new workout, and add new historical summary, return only JSON data at this time.
Why do I have to register for an API key?
It provides 2 things - a way for powertwenty to contact you if needed and a way to block a client in case defects in it are causing problems (such as an infinite loop).
How often can I call the API before the calls are throttled?
The exact number is not published, but it should be plenty for reasonable use of the API. We are actually not concerned with load on the API as much as being good clients of the real Concept 2 Online Logbook. Send an email to firstname.lastname@example.org
if your application is running into the throttling limits and we will work something out.
How are requests throttled?
Requests are throttled by the requestor's IP address.
Why not HTTPS?
Powertwenty is looking into that. However, the Concept 2 Online Logbook itself is exposed only via HTTP at this time so credentials are sent to it in plain text just as they would be if a person used it from a browser.