Emacs mode to edit JSON

Does anybody know a good Emacs mode to edit JSON? An app I am working on uses a JSON based communication protocol and having the data nicely indented and syntax-highlighted would help me a lot in the process of figuring it out.

+1 for Josh's json-mode -- works well for me. I added

(defun beautify-json ()
  (interactive)
  (let ((b (if mark-active (min (point) (mark)) (point-min)))
        (e (if mark-active (max (point) (mark)) (point-max))))
    (shell-command-on-region b e
     "python -m json.tool" (current-buffer) t)))

and

(define-key json-mode-map (kbd "C-c C-f") 'beautify-json)

to json-mode.el to make the shell command invocation easier.

UPDATE: For those of you with a need/desire to do this with unicode, see my question here. The upshot is rather than using:

python -m json.tool

you will want to use

python -c 'import sys,json; data=json.loads(sys.stdin.read()); print json.dumps(data,sort_keys=True,indent=4).decode("unicode_escape").encode("utf8","replace")'

This both beautifies the JSON as well as preserving the original Unicode content.

js-mode supports syntax highlighting and indentation for json files.

This is as of Emacs 23.2, when espresso-mode was incorporated into Emacs and renamed js-mode.

Check it out: http://www.nongnu.org/espresso/

Have you tried Steve Yegge's js2-mode for Emacs?

If you want something lightweight try this major-mode I hacked together: https://github.com/joshwnj/json-mode

It's actually no more than some extra syntax highlighting on top of javascript-mode, but for my purposes I've found it to work quite well.

Another common use-case is auto-formatting a JSON file (eg. if it's whitespace-compressed and you want more readability). To do this I'm just piping the buffer through a command-line script: C-u M-|

I've prepared a workaround for js2-mode so it parses json files without errors. You can find it in my comment: http://code.google.com/p/js2-mode/issues/detail?id=50#c7

(I wanted to post it as a comment do J.F. Sebastian solution, but it seems I'm not allowed to do so (no 'add comment' link))

json.el by Edward O'Connor is part of GNU Emacs since 23.1 (2008).

While it isn't a syntax highlighter, it has a useful function to format JSON:

M-x json-pretty-print-buffer RET

So, if you have a recent version of Emacs, there is no need for jq or python -m json.tool.

Since JSON is a subset of YAML, yaml-mode works too (I don't know how it compares to js-mode and json-mode, though).

Install (from emacs): M-x package-install yaml-mode.

Association of yaml-mode with YAML and JSON files, in ~/.emacs.d/init.el:

(add-to-list 'auto-mode-alist '("\\.yaml$" . yaml-mode))
(add-to-list 'auto-mode-alist '("\\.json$" . yaml-mode))

JSON is supported by espresso-mode

js3-mode:https://github.com/thomblake/js3-mode

js3-mode is an improved js2-mode

This package can be installed by package-list-packages command

I will also second Josh's json-mode, but also recommend flymake-json as an addition. It helps highlight syntax errors.

I don't like using python -mjson.tool because it reorders items in JSON objects. I find (prog-indent-sexp) works just fine to reindent, and using jsonlint instead of python -mjson.tool works for pretty printing/reformatting in beautify-json

(eval-after-load "json-mode"
  '(progn
     (require 'flymake-json)
     ;; flymake-cursor displays error in minibuffer message area instead of requiring hover
     (require 'flymake-cursor)

     (add-hook 'json-mode-hook 'flymake-json-load)
     (define-key json-mode-map "\C-c\C-n" (function flymake-goto-next-error))
  )
)

I've expanded on Mariusz Nowak's workaround, to make it usable as a major mode in its own right. Little modification was required beyond simply deriving the mode; the only change Nowak's work actually needed was the ability to recognize buffers not associated with files, or associated with files whose names don't end in .json, as JSON, which we accomplish with a buffer-local variable.

Here's the augmented workaround:

(make-variable-buffer-local 'js2-parse-as-json)

(defadvice js2-reparse (before json)
	(setq js2-buffer-file-name buffer-file-name))
(ad-activate 'js2-reparse)

(defadvice js2-parse-statement (around json)
	(if (and (= tt js2-LC)
           js2-buffer-file-name
           (or js2-parse-as-json
               (string-equal (substring js2-buffer-file-name -5) ".json"))
           (eq (+ (save-excursion
                    (goto-char (point-min))
                    (back-to-indentation)
                    (while (eolp)
                      (next-line)
                      (back-to-indentation))
                    (point)) 1) js2-ts-cursor))
      (setq ad-return-value (js2-parse-assign-expr))
		ad-do-it))
(ad-activate 'js2-parse-statement)

(define-derived-mode json-mode js2-mode "JSON"
  "Major mode for editing JSON data."
  :group 'json
  (setq js2-parse-as-json t)
  (js2-reparse t))

(add-to-list 'auto-mode-alist '("\\.json$" . json-mode))

If you already use js2-mode, this may be a better option than js-mode plus flymake-json because you need not install anything new (js2-mode already does syntax checking, no need for an external tool), and because this mode will inherit your js2-mode configuration, which js-mode will not.

I would also recommand js2-mode.

JSON stands for JavaScript Object Notation. It's not another language and it's even not a data container like yaml or xml are. JSON could be used as a data container if there's no function (or in this case we should say method) inside a JSON object, but it's not the primary goal of JSON :-)

var myJSObject = {
  attr: {foo: "bar", baz: ["quux", "truc", "pouet"]},
  fooAlert: function (num) {
    alert(this.attr.foo+' '+num);
  }
};
myJSObject.fooAlert(42);