Assuming you take care of the essentials like documentation and code samples, following will make your API shine. * Explanatory Error Responses: Tell what was

Assuming you take care of the essentials like documentation and code samples, following will make your API shine. * Explanatory Error Responses: Tell what was wrong in a problematic request and, potentially, how to fix the request * Introspection end points: Which can tell you more about the request (headers/body) and credentials (rate limits, app id, etc) observed by the server. Is very handy in case of debugging. * API should be able to tell properly when its unavailable. Ideally by returning proper HTTP 503 response.