Can we say “If an API is following 6 constraints of REST then it’s a RESTful API”?

Question

Can we say “If an API is following 6 constraints of REST then it's a RESTful API”? or my statement is completely wrong?

Answer 1

Well, you are half right. Yes, there are 6 constraints that Mr. Roy Fielding described in his phD publication. But, the last one "Code On Demand" is optional

Ref: https://www.ics.uci.edu/~fielding/pubs/dissertation/rest_arch_style.htm

Answer 2

Can we say “If an API is following 6 constraints of REST then it's a RESTful API”? or my statement is completely wrong?

You probably need to be detailed about the nature of the "uniform interface" constraint:

REST is defined by four interface constraints: identification of resources; manipulation of resources through representations; self-descriptive messages; and, hypermedia as the engine of application state.

See also REST APIs Must be Hypertext Driven (Fielding 2008).

Answer 3

REST defines 6 architectural constraints which make any web service – a true RESTful API.

1. Uniform interface
2. Client-server
3. Stateless
4. Cacheable
5. Layered system
6. Code on demand ( optional )

All the above constraints help you build a truly RESTful API, and you should follow them. Still, at times, If you find yourself violating one or two constraints. Do not worry; you are still making a RESTful API – but not “truly RESTful.”