From Joomla! Documentation
This article or section is in the process of an expansion or major restructuring. You are welcome to assist in its construction by editing it as well. If this article or section
You will learn about response types you will be able to receive from the system.
Specifying response format by query parameter
You should add the query parameter format to your request. That will specify the content type you would like to receive from server. The values of the parameter format that you can use are html, json, jsonapi, image, feed, xml, raw.