mark the json text below and run M-x json-pretty-print
{"t": "hello"}
Debugger entered--Lisp error: (json-key-format t)
signal(json-key-format (t))
json-pretty-print(1 15 nil)
funcall-interactively(json-pretty-print 1 15 nil)
call-interactively(json-pretty-print record nil)
command-execute(json-pretty-print record)
execute-extended-command(nil "json-pretty-print" "json")
funcall-interactively(execute-extended-command nil "json-pretty-print" "json")
call-interactively(execute-extended-command nil nil)
command-execute(execute-extended-command)