To facilitate regular updates and better accuracy, we have moved reference documentation for APIs to the CommCare project technical documentation, hosted on ReadTheDocs:
This reference documentation goes over each individual API, with details about each accepted parameter, response format, and URL paths. You'll still find some high-level usage documentation on the CommCare Help Site, as well as a link to the above, should you need to find it again later. See here for the API home on the help site: