this is a sublime text 3 plugin to format selected (or all file) JSON text.

format_json.py

#
# Copy this file into the user package directory (eg. to C:\Users\Rui Lopes\AppData\Roaming\Sublime Text 3\Packages\User).
# NB you can go into this directory by opening the Preferences | Browse Packages... menu.
#
# Add a shortcut to run this command by using sublime Preferences | Key Bindings - User:
#
# [
#  {
#    "keys": ["ctrl+shift+j"],
#    "command": "format_json"
#  }
# ]
#
#
# Also, create a file named Main.sublime-menu (eg. at C:\Users\rgl\AppData\Roaming\Sublime Text 2\Packages\User\) to
# add this command to Selection menu:
#
# [
#   {
#     "id": "selection",
#     "caption": "Selection",
#     "children": [
#       {
#         "id": "format",
#         "caption": "Format",
#         "children": [
#           {
#             "caption": "Format JSON",
#             "command": "format_json"
#           }
#         ]
#       }
#     ]
#   }
# ]
#
# For a XML formatter see https://gist.github.com/rgl/5884996

import sublime
import sublime_plugin
import re
import json
import collections

# See http://www.sublimetext.com/docs/3/api_reference.html

class FormatJsonCommand(sublime_plugin.TextCommand):
  def run(self, edit):
    try:
      selections = self.view.sel()

      # if there is no selected text, apply to all text.
      if len(selections) == 1 and selections[0].empty():
        selections = [sublime.Region(0, self.view.size())]

      for sel in selections:
        text = self.view.substr(sel)

        obj = json.loads(text, object_pairs_hook=collections.OrderedDict)

        formatted_json = json.dumps(obj, sort_keys=False, indent=4, separators=(',', ': '))

        self.view.replace(edit, sel, formatted_json)

    except Exception as e:
      sublime.error_message(u"ERROR formating JSON: %s" % e)

  def clear(self):
    self.view.erase_status('tidy_json')