simplejson

Simple, fast, extensible JSON encoder/decoder for Python

simplejson Permissive license MIT OR AFL-2.1 Active ★ 1,712 v4.1.1 released 2026-04-24

Install

simplejson on PyPI

pip

pip install simplejson

uv

uv add simplejson

poetry

poetry add simplejson

Package facts

License	MIT OR AFL-2.1 (permissive)
Python support	supports the current Python release (!=3.0.,!=3.1.,!=3.2.,!=3.3.,!=3.4.,!=3.5.,!=3.6.,!=3.7.,>=2.7)
Install friction	low — pure-Python wheel
Runtime dependencies	none
Maintenance	actively maintained — 111 days since the last release
Last repo commit	2026-08-06
First released	2005-12-31
Popularity	one of the top 1,000 most-downloaded packages on PyPI (30-day window, as of 2026-08-13)
Known vulnerabilities	none known (OSV.dev, checked 2026-08-13)

Evidence: simplejson-4.1.1-py3-none-any.whl

Development Status :: 5 - Production/StableEnvironment :: WebAssembly :: EmscriptenIntended Audience :: DevelopersProgramming Language :: PythonProgramming Language :: Python :: 2Programming Language :: Python :: 2.7Programming Language :: Python :: 3Programming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.8Programming Language :: Python :: 3.9Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: GraalPyProgramming Language :: Python :: Implementation :: PyPyTopic :: Software Development :: Libraries :: Python Modules

About simplejson

from the package's own PyPI description — quoted content, verbatim

simplejson

simplejson is a simple, fast, complete, correct and extensible JSON <http://json.org> encoder and decoder for Python 3.8+ with legacy support for Python 2.7. It is pure Python code with no dependencies, but includes an optional C extension for a serious speed boost.

The latest documentation for simplejson can be read online here: https://simplejson.readthedocs.io/

simplejson is the externally maintained development version of the json library included with Python (since 2.6). This version is tested with Python 3.14 (including free-threaded builds) and maintains backwards compatibility with Python 3.8+. A legacy Python 2.7 wheel is also published.

The encoder can be specialized to provide serialization in any kind of situation, without any special support by the objects to be serialized (somewhat like pickle). This is best done with the default kwarg to dumps.

The decoder can handle incoming JSON strings of any specified encoding (UTF-8 by default). It can also be specialized to post-process JSON objects with the object_hook or object_pairs_hook kwargs. This is particularly useful for implementing protocols such as JSON-RPC that have a...

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AI interpretation — verify before relying

AI-generated interpretation of the package facts above; every digit, version, license, or vulnerability id it cites is grounded in the facts already shown on this page

simplejson is a fast, complete JSON encoder and decoder for Python 3.8+ (with Python 2.7 legacy support) that offers specialized serialization and deserialization hooks, plus an optional C extension for performance.

Low friction: pure Python with no runtime dependencies, distributed as a wheel. Actively maintained with recent commits and 1712 repository stars; last release 111 days ago signals ongoing support.

Licensed under MIT OR AFL-2.1 (permissive); either license permits commercial and private use with minimal restrictions, making it suitable for most projects.

Usage

pip install simplejson
import simplejson
data = {"key": "value"}
json_str = simplejson.dumps(data)
parsed = simplejson.loads(json_str)

Requires Python 2.7 or Python 3.8+; C extension is optional and not required for functionality.

Verdict: simplejson is a mature, actively maintained JSON library with zero known vulnerabilities, no dependencies, and broad Python version support. Its permissive dual license and low install friction make it a reliable choice for projects needing JSON serialization with customization hooks or performance optimization via its optional C extension.

Needs verification

Performance characteristics of the optional C extension relative to the pure Python implementation
Compatibility details with free-threaded Python builds mentioned in classifiers

json encoder decoder pythonfast json serializationjson with custom hookspython json library alternativejson parsing python 3extensible json encoderrawjson embedding