On most pages you can even just open the inspector (cmd alt i) and do $.get() to inspect json from random places
http://json.parser.online.fr/
curl 'http://api.twitter.com/1/statuses/user_timeline.json?screen_name=twitter&include_rts=1 | prettify_json.rb| less
curl "http://api.twitter.com/1/statuses/user_timeline.json?screen_... | python -m json.tool | pbcopy