The aeson package

[Tags:bsd3, library, test]

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

To get started, see the documentation for the Data.Aeson module below.

Parsing performance on an early 2011 MacBook Pro (2.2GHz Core i7), running 64-bit GHC 7.6.3, 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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Change log changelog
Dependencies attoparsec (>=, base (==4.*), blaze-builder (>=, bytestring, containers, deepseq, dlist (>=0.2), ghc-prim (>=0.2), hashable (>=, mtl, old-locale, scientific (==0.2.*), syb, template-haskell (>=2.4), text (>=, time (<1.5), unordered-containers (>=, vector (>=0.7.1) [details]
License BSD3
Copyright (c) 2011, 2012, 2013 Bryan O'Sullivan (c) 2011 MailRank, Inc.
Author Bryan O'Sullivan <>
Maintainer Bryan O'Sullivan <>
Category Text, Web, JSON
Home page
Bug tracker
Source repository head: git clone git://
head: hg clone
Uploaded Tue Feb 4 06:55:31 UTC 2014 by BryanOSullivan
Updated Sat Apr 11 14:07:19 UTC 2015 by AdamBergmark to revision 2
Distributions Arch:, Debian:, Fedora:, FreeBSD:, LTSHaskell:, NixOS:, Stackage:, Tumbleweed:
Downloads 290459 total (11729 in the last 30 days)
12 []
Status Docs available [build log]
Successful builds reported [all 1 reports]
Hackage Matrix CI




developeroperate in developer modeDisabledAutomatic
blaze-builderUse blaze-builder instead of bytestring >= 0.10DisabledAutomatic
new-bytestring-builderUse the new bytestring builder available in bytestring >=

Use -f <flag> to enable a flag, or -f -<flag> to disable that flag. More info


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.

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,