The Richardson Maturity Model assesses your API according to the constraints of REST. Higher the score true RESTful API it is. The Richardson Maturity Model defines 4 levels (0-3), where level 3 designates a fully true RESTful API.
Level 0 : Expose SOAP web services in REST style. Expose action based services for example (http://server/getFavorites, http://server/deleteFavorites) using REST.
Level 1 :Create resources with proper URIs (using nouns). Ex: http://server/accounts, http://server/accounts/10. However, HTTP Methods are not used.
Level 2 : Resources use proper URI's + HTTP Methods. For example, to update an account, you do a PUT to. The create an account, you do a POST to. Uri's look like posts/1/comments/5 and accounts/1/friends/1.
Level 3 : HATEOAS (Hypermedia as the engine of application state). You will tell not only about the information being requested but also about the next possible actions that the service consumer can do. When requesting information about a Facebook user, a REST service can return user details along with information about how to get his recent posts, how to get his recent comments and how to retrieve his friend's list.