'camelCase' is the JavaScript standard. Since JSON is an extension of JavaScript I would stick with that.

Ex. allTrue, charAt(), indexOf, ect.

Mozzila's JSON examples are in 'camelCase': https://developer.mozilla.org/en-US/docs/Learn/JavaScript/Ob...

Microsofts's JSON examples are in 'camelCase': https://msdn.microsoft.com/en-us/library/hh923971(v=vs.85).a...