The aeson package

[Tags:bsd3, library, test]

A JSON parsing and encoding library optimized for ease of use and high performance.

Note: if you use GHCi or Template Haskell, please see the README file for important details about building this package, and other packages that depend on it:

Parsing performance on a late 2010 MacBook Pro (2.66GHz Core i7), for mostly-English tweets from Twitter's JSON search API:

Handling heavily-escaped text is a little more work. Here is parsing performance with Japanese tweets, where much of the text is entirely Unicode-escaped.

Encoding performance on the same machine and data:

(A note on naming: in Greek mythology, Aeson was the father of Jason.)

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Versions,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,, (info)
Dependencies attoparsec (>=, base (>=4 && <4.5), blaze-builder (>=, blaze-textual (>=, bytestring, containers, deepseq (<1.2), hashable (>= && <1.2), mtl, old-locale, syb, template-haskell (>=2.5), text (>=, time, unordered-containers (>=, vector (>=0.7) [details]
License BSD3
Copyright Copyright 2011 MailRank, Inc.
Author Bryan O'Sullivan <>
Maintainer Bryan O'Sullivan <>
Stability experimental
Category Text, Web, JSON
Home page
Bug tracker
Source repository head: git clone
head: hg clone
Uploaded Mon Sep 19 18:46:14 UTC 2011 by BryanOSullivan
Updated Wed Nov 4 13:43:34 UTC 2015 by AdamBergmark to revision 2
Distributions Arch:, Debian:, Fedora:, FreeBSD:, LTSHaskell:, NixOS:, Stackage:, Tumbleweed:
Downloads 230887 total (227 in the last 30 days)
11 []
Status Docs uploaded by user
Build status unknown [no reports yet]




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Maintainer's Corner

For package maintainers and hackage trustees

Readme for aeson

Readme for aeson-

Welcome to aeson

aeson is a fast Haskell library for working with JSON data.

Important note for users of GHCi and Template Haskell

This package depends on the blaze-textual package , and is unfortunately subject to crashes if you use GHCi or Template Haskell in your work.

For complete details, including a workaround, see the writeup in the blaze-textual README.

Join in!

We are happy to receive bug reports, fixes, documentation enhancements, and other improvements.

Please report bugs via the github issue tracker.

Master git repository:

  • git clone git://

There's also a Mercurial mirror:

  • hg clone

(You can create and contribute changes using either git or Mercurial.)


This library is written and maintained by Bryan O'Sullivan,