When developing an API, one of the first critical decisions every developer must face is that of Content Type. In this day and age most APIs return one or both of JSON or XML.
Some APIs get away with one, and that’s fine, but to improve the UX of your API, you should allow the requestor to determine what data type is best for them. If you’ve read the post on API Content Negotiation, you’ll know the best way to approach content negotiation is to follow the standards.