Why are GET requests returning JSON disallowed by default?

Question

As part of the ASP.NET MVC 2 Beta 2 update, JSON GET requests are disallowed by default. It appears that you need to set the JsonRequestBehavior field to

Answer 1

I don't know if this is the reason they chose to change that default, but here's my experience:

When some browsers see a GET, they think they can cache the result. Since AJAX is usually used for small requests to get the most up-to-date information from the server, caching these results usually ends up causing unexpected behavior. If you know that a given input will return the same result every time (e.g. "password" cannot be used as a password, no matter when you ask me), then a GET is just fine, and browser caching can actually improve performance in case someone tries validating the same input multiple times. If, on the other hand, you expect a different answer depending on the current state of the server-side data ("myfavoriteusername" may have been available 2 minutes ago, but it's been taken since then), you should use POST to avoid having the browser thinking that the first response is still the correct one.