As per title. The code box does not have support for JSON specifically. Is it possible to add it?

Well, right after posting I figured out that selecting Javascript does support it. Instead of "adding support for it", can you change the language string to list it after the name with parenthesis? Kinda like you do already for C Language.

 

And related to the code box, I am actually wondering why every time I open it I get that loading image for a while before I can finally use it. Is there any need for it when loading an empty code box?

It loads from the server which is why you get a loading icon. It's something I've wanted to look at changing but haven't had a chance to.