Extract and apply patches to JSON documents.

LTS Haskell 9.9:
Stackage Nightly 2017-10-20:
Latest on Hackage:
BSD3 licensed by Thomas Sutton
Maintained by

Module documentation for

Aeson Diff

Build Status Hackage Hackage-Deps

This is a small library for working with changes to JSON documents. It includes a library and two executables in the style of diff(1) and patch(1). Patches are themselves JSON Patch documents as specified in RFC 6902.


The aeson-diff package is written in Haskell and can be installed using the Cabal package management tool, stack, or something similar.

bash stack install aeson-diff

The command-line tools can then be executed using stack:

stack exec json-diff -- .... stack exec json-patch -- ....

If you prefer to use Cabal, something like this might do the trick:

bash cd aeson-diff/ cabal sandbox init cabal install --dependencies-only cabal build sudo mkdir -p /usr/local/bin sudo cp dist/build/json-*/json-{diff,patch} /usr/local/bin/


Patch format

aeson-diff supports the JSON Patch format described in RFC 6902.

json-diff command

The json-diff command compares two JSON documents and extracts a patch describing the differences between the first document and the second.

Usage: json-diff [-T|--test-before-remove] [-o|--output OUTPUT] FROM TO Generate a patch between two JSON documents.

Available options: -h,--help Show this help text -T,--test-before-remove Include a test before each remove. -o,--output OUTPUT Write patch to file OUTPUT.

json-patch command

The json-patch command applies a patch describing changes to be made to a JSON document.

Usage: json-patch [-o|--output OUTPUT] PATCH FROM Generate a patch between two JSON documents.

Available options: -h,--help Show this help text -o,--output OUTPUT Destination for patched JSON. PATCH Patch to apply. FROM JSON file to patch.

aeson-diff library

The aeson-diff library exports as single module: Data.Aeson.Diff. This exports diff and patch functions which do exactly what might be expected:

  • diff :: Value -> Value -> Patch examines source and target JSON Values and constructs a new Patch describing the changes.

  • patch :: Patch -> Value -> Result Value applies the changes in a Patch to a JSON Value. If an error results then an exception is thrown.

For more complete information, see the documentation.



* Resolve name clash that prevents building against aeson>=1.2 in
  Stackage Nightly.


* Relax upper bound on base dependency for Stackage LTS-9.


* aeson-diff can now, optionally, generate a test operation before each

* Add '--test-before-remove' option to 'json-diff' command.

* Add 'Config' type and 'diff'' to allow optional behaviours.


* Remove the `patch'` function before anyone gets attached to it.

* Remove the 'Value' which was carried by the 'Rem' operation constructor.

* Move 'Pointer' and 'Patch' types and operations into separate modules.

aeson-diff 1.0

* aeson-diff now supports the operations and patch format described in
  RFC 6902.

* The `patch` function now returns in the 'Result' monad from the aeson

* Add a `patch'` function throws an exception instead.

* The command line applications no longer pretend to support a non-JSON
  patch format.

aeson-diff 0.1

* Initial release.
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