ujson

Ultra fast JSON encoder and decoder for Python

ujson Permissive license BSD-3-Clause AND TCL Active ★ 4,495 v5.13.0 released 2026-06-14

Install

ujson on PyPI

pip

pip install ujson

uv

uv add ujson

poetry

poetry add ujson

Package facts

License	BSD-3-Clause AND TCL (permissive)
Python support	supports the current Python release (>=3.10)
Install friction	medium — platform-specific wheel
Runtime dependencies	none
Maintenance	actively maintained — 60 days since the last release
Last repo commit	2026-08-01
First released	2011-06-16
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: ujson-5.13.0-cp310-cp310-macosx_10_9_x86_64.whl; ujson-5.13.0-cp310-cp310-macosx_11_0_arm64.whl; ujson-5.13.0-cp310-cp310-manylinux1_i686.manylinux2014_i686.manylinux_2_17_i686.manylinux_2_5_i686.whl; ujson-5.13.0-cp310-cp310-manylinux2014_aarch64.manylinux_2_17_aarch64.whl; ujson-5.13.0-cp310-cp310-manylinux2014_x86_64.manylinux_2_17_x86_64.whl; ujson-5.13.0-cp310-cp310-manylinux_2_24_aarch64.manylinux_2_28_aarch64.whl; ujson-5.13.0-cp310-cp310-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl; ujson-5.13.0-cp310-cp310-musllinux_1_2_aarch64.whl; ujson-5.13.0-cp310-cp310-musllinux_1_2_i686.whl; ujson-5.13.0-cp310-cp310-musllinux_1_2_x86_64.whl; ujson-5.13.0-cp310-cp310-win32.whl; ujson-5.13.0-cp310-cp310-win_amd64.whl; ujson-5.13.0-cp310-cp310-win_arm64.whl; ujson-5.13.0-cp311-cp311-macosx_10_9_x86_64.whl; ujson-5.13.0-cp311-cp311-macosx_11_0_arm64.whl; ujson-5.13.0-cp311-cp311-manylinux1_i686.manylinux2014_i686.manylinux_2_17_i686.manylinux_2_5_i686.whl; ujson-5.13.0-cp311-cp311-manylinux2014_aarch64.manylinux_2_17_aarch64.whl; ujson-5.13.0-cp311-cp311-manylinux2014_x86_64.manylinux_2_17_x86_64.whl; ujson-5.13.0-cp311-cp311-manylinux_2_24_aarch64.manylinux_2_28_aarch64.whl; ujson-5.13.0-cp311-cp311-manylinux_2_24_x86_64.manylinux_2_28_x86_64.whl

Development Status :: 5 - Production/StableIntended Audience :: DevelopersProgramming Language :: CProgramming Language :: Python :: 3 :: OnlyProgramming Language :: Python :: 3.10Programming Language :: Python :: 3.11Programming Language :: Python :: 3.12Programming Language :: Python :: 3.13Programming Language :: Python :: 3.14Programming Language :: Python :: 3.15Programming Language :: Python :: Implementation :: CPythonProgramming Language :: Python :: Implementation :: GraalPyProgramming Language :: Python :: Implementation :: PyPyTyping :: Typed

About ujson

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

UltraJSON

PyPI version (image) Supported Python versions (image) PyPI downloads (image) GitHub Actions status (image) codecov (image) DOI (image) Code style: Black (image)

UltraJSON is an ultra fast JSON encoder and decoder written in pure C with bindings for Python.

Install with pip:

python -m pip install ujson

Project status

> [!WARNING] > UltraJSON's architecture is fundamentally ill-suited to making changes without > risk of introducing new security vulnerabilities. As a result, this library > has...

Read as markdown · JSON record · Source repository · Homepage

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

Ultra-fast JSON encoder and decoder written in C with Python bindings, offering a drop-in replacement for standard JSON libraries with optional HTML escaping, ASCII enforcement, and pretty-printing.

Medium install friction due to compiled C extensions requiring platform-specific wheels; however, wheels are provided for Python 3.10–3.15 across macOS, Linux (multiple architectures), and Windows, and the package is actively maintained with a recent release.

Dual-licensed under BSD-3-Clause and TCL (permissive), allowing commercial and private use with minimal restrictions; attribution and license text inclusion are required.

Usage

pip install ujson
import ujson
result = ujson.dumps({"key": "value"})
data = ujson.loads('[{"key": "value"}, 81, true]')

Requires Python 3.10 or later; compiled C extension wheels must match your platform and Python version.

Verdict: Actively maintained, production-stable JSON library with no known vulnerabilities and strong platform coverage. Maintenance-only status and explicit recommendation to migrate to orjson for new projects signal architectural limitations, but it remains a solid choice for existing codebases requiring fast JSON processing without introducing new dependencies.

Needs verification

Whether medium install friction materially impacts typical deployment workflows or is offset by wheel availability
Real-world performance gains versus standard library json in typical application scenarios
Scope and likelihood of the buffer overflow vulnerabilities mentioned in the maintenance warning

fast json encoder decoderhigh performance json parsingc json library pythonjson serialization speedultra fast jsonjson performance optimizationdrop-in json replacement