Restful Webservices comparison WebAPI vs MVC

Question

I was told to design an API for a client to manipulate some data. Now, trying to keep up with the Jones', I've designed this using WebAPI. I post to my Restful Webservice an object via $.Ajax

Why is this any different from using the same $.Ajax to post to a standard MVC 4.0 Controller?

What are the advantages?

Thanks

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With regard to potential answer:

Note If you have worked with ASP.NET MVC, then you are already familiar with controllers. They work similarly in Web API, but controllers in Web API derive from the ApiController class instead of Controller class. The first major difference you will notice is that actions on Web API controllers do not return views, they return data.

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Wouldn't this still be redundant, after all you can always

return JSON(x);

from any MVC controller.

Answer 1

http://encosia.com/asp-net-web-api-vs-asp-net-mvc-apis/

ASP.NET Web API vs. ASP.NET MVC “APIs” by Dave Ward --Thanks Ant P

A beautiful synopsis:

• Content negotiation
• Flexibility
• Separation of concerns