<i>Every REST interface I have tried to integrate with uses HTTP error codes differently, treats the GET/POST/PUT/DELETE commands in its own peculiar way, and has unique requirements for authentication.</i><p>I can't defend systems that (for example) misuse HTTP status codes or ignore HTTP authentication, but this puts it at the same level as XML-RPC, which re-invents error codes, methods, and authentication <i>every time</i>.<p><i>documentation of data structures, calling conventions, and error codes is essential, and just saying "we use HTTP" is insufficient to communicate these details.</i><p>I absolutely agree. Documentation is essential for a web service, regardless of how you provide that service.