json-delta is a set of command-line tools and multi-language libraries for diffing and patching JSON files. The tools includes:

  • json_cat: concatenates the JSON file
  • json_diff: outputs diff of two JSON files
  • json_patch: applies patch from json_diff onto a JSON file

The supported languages include Python 2.7+ and 3+, JavaScript, Racket, and Perl. For languages other than Python, you need to get from its repository.

Consider the following two files, foo and bar:

{"foods": ["spam", "spam", "spam", "spam"],
 "weaponry": "Mainly battleaxes.",
 "spanish inquisition expected": false,
 "drinks": "Delicious mead!",
 "other supplies": null}

{"foods": ["spam", "spam", "spam", "pickled eggs", "spam"],
 "weaponry": "Mainly battleaxes.",
 "spanish inquisition expected": false,
 "drinks": "Soda water."}

Now, diff with json_diff:

$ json_diff foo bar
Size of delta 67.808% size of original (original: 146 chars, delta: 99 chars)

[[["other supplies"]],[["drinks"],"Soda water."],[["foods",3],"pickled eggs"],[["foods",4],"spam"]]

Using the unified option -u:

$ json_diff -u foo bar
Size of delta 67.808% size of original (original: 146 chars, delta: 99 chars)
--- foo 2014-04-29 14:04:49 CST
+++ bar 2014-04-29 14:04:11 CST
 {
  "weaponry": "Mainly battleaxes.",
  ...,
  "foods":
   [
    "spam",
    ...(1),
    "spam",
-   "spam"
+   "pickled eggs",
+   "spam"
   ],

- "other supplies": null,

  "drinks":
-  "Delicious mead!"
+  "Soda water."
 }

To patch the foo and output to standard output:

$ json_patch foo <(json_diff foo bar)
Size of delta 67.808% size of original (original: 146 chars, delta: 99 chars)

{"foods": ["spam", "spam", "spam", "pickled eggs", "spam"], "weaponry": "Mainly battleaxes.", "spanish inquisition expected": false, "drinks": "Soda water."} /tmp $

By default, it’s not in-place patching, but you can use --output to overwrite the original file or any other file.

json-delta is written by Philip J. Roberts under the Simplified BSD License (2-clause), currently version 0.1 (2014-04-15).