Here's the begining of the terms of service for the API. It will evolve based on user feedback and experience so please check it from time to time.
If you have any doubt, don't hesitate to ask, we are happy to help!
TrackMania Web Services usage guidelines
- You may not store the data permanantly in your application ; you can use some caching mechanism to improve performance and reduce request rate, but you must try to keep the data as up to date as possible.