“The Richardson Maturity Model can be used for determining the degree to which services are RESTful. The following levels are defined: Level 0: Services use an RPC style. Level 1: Services expose resources. Larger services are broken down into resources. Level 2: Services use HTTP methods correctly. Services use HTTP infrastructure efficiently. Level 3: Hypermedia is used according to HATEOAS. The service is self-documenting and flexible.”