I've copied rest.php from core/config to app/config and modified default_format to json but if i don't append '.json' to the URL I still get response in XML format.
How can I get response in JSON on URLs without format?
To determine the format in which the result should be returned, the REST controller uses the following algorithm and selects the first that is found:
If you're performing an AJAX request you'll want to send up some accept headers up with the request. It's considered bad practice to hard code the response type server side.