If you really want an "editor", you could check out the graphical JSON editor included with the ruby json package: http://json.rubyforge.org/screenshots.html
I only want an editor to fiddle with (tidy up) some data, which is in JSON format becasue it was exported from the django dumpdata command.
As it's a one off task - I didn't really want to get into writing a script.
Cheers