This report is out-of-date.

The state of things has changed dramatically, for the better, since I first wrote this in early 2008. Although my test cases are still quite useful, any information regarding specific python packages is likely to be inaccurate. I am leaving these pages here primarily for historic interest.

As of March 20, 2008

In this report I've attempted to rigorously compare many of the currently available Python language modules for manipulating JSON encoded data. My primary intent is to determine how well each module conforms to the JSON specification, as documented in RFC 4627, as well as identifying nuances in how each maps various Python language constructs to JSON constructs.

Although credit is due to JSON creator Douglas Crockford for one of the simplest language-independent data interchange formats; it can still be deceptively easy to implement correctly. I hope my rigor here helps all software authors to improve their offerings; and in the end improves data interchange and interoperability for everybody. Perhaps even those implementing JSON in other programming languages may find something useful here.

One of the modules analyzed, demjson, is my own creation. Regardless, I've tried to remain objective in my analysis. I do welcome any feedback or corrections. Please remember that software rarely stands still, so when you read this report the state of the software may have changed‒hopefully for the better.

JSON validators

There are numerous on-the-web validators of JSON, most notably the However those validators, though useful, are not exceptionally rigourous.

For use in Python, there is:

Introducing the modules tested

2008-03-24: Newer versions of jsonlib and simplejson have recently been released, partly to address issues covered by this report. I have not yet updated this report to reflect these new version; please check back in a few days.

These are the JSON modules that I've compared for this report. It is important to note the specific version I've used, as things change.

I am only focusing on modules which provide generic JSON encoding and decoding functionality; no attempt is made to analyze expanded functionality such as JSON-RPC or modules which are too specifically tied to a larger framework to be easily used generically.

If you are looking for something else, a good place to start is to search the PyPI database for all JSON-related Python projects.

Module Version tested Author/
License Minimum
Version Date
demjson 1.3 2008-03-18 Deron Meranda GPL 3.0+ 2.3 Pure python
jsonlib 1.2.5 2008-03-15 John Millikin MIT 2.4 Uses C extension
JsonUtils 0.1 2006-09-18 Russell Moffitt LGPL 2.1+ ? Includes python-json module; adds JSON-RPC functionality.
python-cjson 1.0.5 2007-08-24 Dan Pascu LGPL 2+ ? Uses C extension
python-json 3.4 2005-08-09 Patrick Dlogan LGPL 2.1+ 2.4 ? Pure python
simplejson 1.7.5 2008-03-16 Bob Ippolito MIT 2.3 Optional C speed-up extension


import demjson
# Converting Python to JSON
json_object = demjson.encode( python_object )
# Converting JSON to Python
python_object = demjson.decode( json_object )


import jsonlib
# Converting Python to JSON
json_object = jsonlib.write( python_object )
# Converting JSON to Python
python_object = json_object )


import jsonutils.json
# Converting Python to JSON
json_object = jsonutils.json.write( python_object )
# Converting JSON to Python
python_object = json_object )

This module is excluded from the rest of this report's testing, since it's basic JSON encoding and decoding functionality is identical to that of python-json.


import cjson
# Converting Python to JSON
json_object = cjson.encode( python_object )
# Converting JSON to Python
python_object = cjson.decode( json_object )


import json
# Converting Python to JSON
json_object = json.write( python_object )
# Converting JSON to Python
python_object = json_object )


import simplejson
# Converting Python to JSON
json_object = simplejson.dumps( python_object )
# Converting JSON to Python
python_object = simplejson.loads( json_object )

See also

Go to the next page: Basic JSON