fastjsonschema

Fastest Python implementation of JSON schema

fastjsonschema Permissive license BSD-3-Clause Active ★ 495 v2.22.1 released 2026-07-27

Install

fastjsonschema on PyPI

pip

pip install fastjsonschema

uv

uv add fastjsonschema

poetry

poetry add fastjsonschema

Package facts

License	BSD-3-Clause (permissive)
Python support	supports the current Python release (>=3.10)
Install friction	low — pure-Python wheel
Runtime dependencies	none
Maintenance	actively maintained — 17 days since the last release
Last repo commit	2026-08-09
First released	2016-10-05
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: fastjsonschema-2.22.1-py3-none-any.whl

Development Status :: 5 - Production/StableIntended Audience :: DevelopersLicense :: OSI Approved :: BSD LicenseOperating System :: OS IndependentProgramming Language :: PythonProgramming 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 :: Implementation :: CPythonTopic :: Software Development :: Libraries :: Python Modules

About fastjsonschema

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

=========================== Fast JSON schema for Python ===========================

|PyPI| |Pythons|

.. |PyPI| image:: https://img.shields.io/pypi/v/fastjsonschema.svg :alt: PyPI version :target: https://pypi.python.org/pypi/fastjsonschema

.. |Pythons| image:: https://img.shields.io/pypi/pyversions/fastjsonschema.svg :alt: Supported Python versions :target: https://pypi.python.org/pypi/fastjsonschema

See documentation <https://horejsek.github.io/python-fastjsonschema/>_.

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

fastjsonschema validates JSON data against JSON Schema specifications with a focus on speed, compiling schemas into optimized Python validation code.

Low install friction with no runtime dependencies. The package is actively maintained with a recent release (17 days old) and a stable commit history, supporting Python 3.10 through 3.14.

BSD-3-Clause is a permissive license allowing commercial use, modification, and distribution with minimal restrictions, making this package suitable for most projects.

Usage

pip install fastjsonschema==2.22.1

import fastjsonschema
validate = fastjsonschema.compile({"type": "object"})
validate({"key": "value"})

Requires Python 3.10 or later.

Verdict: fastjsonschema is a production-stable, actively maintained validator with zero known vulnerabilities, no dependencies, and permissive licensing. It's a low-friction choice for JSON Schema validation in modern Python projects.

Needs verification

Whether the claimed performance advantage over standard json schema libraries is significant for typical workloads
Whether the schema compilation approach introduces any runtime overhead on first use

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