fastjsonschema
Fastest Python implementation of JSON schema
Decision gist · record as of 2026-08-14
Yes, if you validate JSON against the same schema repeatedly and performance matters. The zero runtime dependencies and active maintenance make it a low-risk addition. If you validate schemas infrequently or need detailed error reporting, a standard validator may be simpler. No known vulnerabilities as of 2026-08-14.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later.
- Low friction install with no runtime dependencies.
- Actively maintained as of 2026-07-27 with recent commits and a stable codebase; supports Python 3.10 through 3.14.
License · maintenance · safety
BSD-3-Clause (permissive) — BSD-3-Clause permissive license allows use in commercial and proprietary projects with minimal restrictions; attribution required.
last release 2026-07-27 (18 days) · last repo commit 2026-08-09 · 495 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 154,525,318 downloads/mo, #263 on PyPI
Alternatives
Verify before relying
pip install fastjsonschema
import fastjsonschema
validate = fastjsonschema.compile({"type": "object"})
validate({"key": "value"})- Whether the compiled validator approach provides measurable speed gains over standard jsonschema library in typical workloads.
- Whether validation error messages are as detailed as alternatives when schema violations occur.
What it is and what it does
fastjsonschema is a JSON Schema validator that compiles schemas into Python code rather than interpreting them at validation time. This approach trades schema compilation overhead for faster per-validation execution, making it useful when the same schema is applied to many documents. It has no runtime dependencies beyond Python itself and supports current Python versions from 3.10 onward.
The package is positioned as a performance-focused alternative to standard JSON schema validators. It generates optimized validation functions from JSON Schema definitions, which can be called repeatedly on incoming data. This is particularly relevant for high-throughput scenarios like API request validation, data pipeline filtering, or configuration file checking where the schema remains constant but validation happens frequently.
Use it for
- Validate API request bodies against a fixed schema in web frameworks handling many requests.
- Filter or validate records in data pipelines where the same schema applies to thousands of items.
- Check configuration files or data exports against a predefined JSON Schema specification.
- Build schema-driven data validation into ETL processes where performance matters.
- Enforce data contracts in microservices that receive JSON payloads from multiple sources.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes, if you validate JSON against the same schema repeatedly and performance matters.
The zero runtime dependencies and active maintenance make it a low-risk addition. If you validate schemas infrequently or need detailed error reporting, a standard validator may be simpler. No known vulnerabilities as of 2026-08-14.
Install
fastjsonschema on PyPI
Before you install
Low friction install with no runtime dependencies. Actively maintained as of 2026-07-27 with recent commits and a stable codebase; supports Python 3.10 through 3.14.
Requires Python 3.10 or later.
License in practice
BSD-3-Clause permissive license allows use in commercial and proprietary projects with minimal restrictions; attribution required.
Quickstart
pip install fastjsonschema
import fastjsonschema
validate = fastjsonschema.compile({"type": "object"})
validate({"key": "value"})Verify before relying
- Whether the compiled validator approach provides measurable speed gains over standard jsonschema library in typical workloads.
- Whether validation error messages are as detailed as alternatives when schema violations occur.
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 18 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 154,525,318 / month, #263 on PyPI 30-day window, as of 2026-08-14 |
| Known vulnerabilities | None known OSV.dev, checked 2026-08-14 |
| Classifiers | 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 |
Evidence: fastjsonschema-2.22.1-py3-none-any.whl
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See also check-jsonschema · dataclasses-jsonschema · kcidb-io · jschon · kubernetes-validate · trafaret · swagger-spec-validator · flex · colander · ocsf-lib