Although the REST community initially took a stance against metadata for REST APIs, a number of metadata standards have none-the-less emerged over the last couple of years, mainly fueled by the need to document APIs for their consumers.
photo by CCAC North Library
As an added benefit, the same metadata is now often used to generate code (both client and server), create test harnesses, production monitors and perform real-time validation of request and response messages (when applicable). All of these provide a foundation for an improved Quality of Service (QoS) that many enterprises require as they adopt REST for their information architectures.