The common goal of current metadata formats for REST APIs is to specify:
Methods to access these resources (GET, POST, PUT, etc.…)
Parameters that need to be supplied with these methods (Query, Template, HTTP Header, etc.)
Formats of inbound / outbound messages/representations (JSON Schema, XML Schema, Relax NG, etc.)
Status codes and error/fault messages
Documentary information (descriptions, etc.) for all these
WSDL is a good example from SOAP world. What do we have with REST?