REST Content-Type: Should it be based on extension or Accept header?

Question

Should the representation(html, xml, json) returned by a RESTful web service be determined by the url or by the Accept HTTP header?

Answer 1

Since you're mentioning a RESTful web service and not any web service, I would strongly go for what is supported by underlying standard - HTTP 1.1 and its content negotiation that relies on Accept HTTP header.

As I've explained in my answer to Can I change the headers of the HTTP request send by the browser, address (URI) and representation are two distinct pillars of a RESTful design and they do not need to be mixed. One should not abuse URI for embedding acceptable representations when there's Accept header.

Only if your web application is potentially run and used in an environment where's some HTTP header filtering involved by intermediate nodes, then you should support URI-based content negotiation. Truth be told, such intrusive or improperly functioning proxies should be replaced if anyhow possible and feasible.

Cheers!
Shonzilla