RESTful

RESTful describes web services that conform to the Representational State Transfer architectural style for distributed systems. A RESTful service exposes resources identified by universal resource identifiers (URIs) and uses a uniform interface to manipulate resource representations transferred over a stateless protocol, typically HTTP. Clients interact with resources by transferring representations such as JSON or XML.

Core constraints include client-server separation, statelessness, cacheability to improve scalability, a uniform interface that uses standard methods and status codes, a layered system to enable intermediaries, and optional code on demand. The uniform interface emphasizes operations on resources via standard HTTP verbs and the transfer of resource state through representations.

In practice, RESTful APIs usually map HTTP methods to actions: GET retrieves, POST creates, PUT replaces, PATCH modifies, DELETE removes. Resource identifiers are nouns in URLs rather than actions. Status codes provide outcome signals; content negotiation can select representations; JSON is common today.

Hypermedia as the engine of application state (HATEOAS) is a debated constraint; some RESTful services implement it by including hyperlinks in responses to guide clients, but many APIs omit it and rely on fixed endpoints.

RESTful design is widely used for web services and microservices due to its scalability and simplicity, but the term is sometimes applied loosely. When evaluating a RESTful API, consider adherence to core constraints, consistency of resource modeling, and the extent of hypermedia and versioning strategies.