format-all not formatting json files

[parrotcar00]

I've installed jsonnnetfmt such that which jsonnetfmt gives the location for the binary.

I then opened a foo.json file and did: M-x format-all-buffer at which point, I get the prompt:
Formatter for Javascript:

I entered prettier and I as you would expect I get an error because it's trying to use javascript formatter on json file.

Am I doing something wrong? How do I use format-all to format json files?

[lassik]

If the buffer in js-mode or json-mode? format-all uses the Emacs mode to determine the programming language.