ujson
Ultra fast JSON encoder and decoder for Python
Decision gist · record as of 2026-08-14
Yes-with-conditions. Install if you have an existing ujson dependency or need drop-in compatibility with code already using it. Do not install for new projects: the maintainers explicitly recommend orjson instead, citing both superior performance and lower architectural risk. The maintenance-only status and acknowledged security concerns make this suitable only for stable, low-change workloads.AI-flagged interpretation of the facts on this page — verify before relying
Before you install
- Requires Python 3.10 or later; compiled wheels available for common platforms but may require build tools on unsupported architectures.
- Medium install friction due to compiled C bindings requiring platform-specific wheels, but well-maintained with recent releases and broad platform coverage (macOS, Linux, Windows, multiple architectures).
- Actively maintained with support for current Python versions.
License · maintenance · safety
BSD-3-Clause AND TCL (permissive) — Dual-licensed under BSD-3-Clause and TCL (permissive licenses), imposing no restrictions on commercial or proprietary use.
last release 2026-06-14 (61 days) · last repo commit 2026-08-13 · 4,496 stars
0 known vulnerabilities (OSV.dev, 2026-08-14) · 34,789,130 downloads/mo, #754 on PyPI
Alternatives
Verify before relying
pip install ujson
import ujson
ujson.dumps({"key": "value"})
ujson.loads('{"key": "value"}')- Whether performance gains justify migration from standard json library for typical workloads (benchmarks show variability across test cases).
- Current security posture given maintenance-only status and known architectural limitations acknowledged in project documentation.
What it is and what it does
UltraJSON is a C-based JSON encoder and decoder designed as a faster alternative to Python's standard json library. It provides the same core API (dumps/loads) with optional parameters for HTML character encoding, ASCII enforcement, forward-slash escaping, and pretty-printing. The package has no runtime dependencies and works thread-safely without global state.
The project is in maintenance-only mode: new Python version support and critical security fixes are applied, but architectural changes are rejected due to security concerns inherent in the C implementation. The maintainers explicitly recommend migration to orjson for new projects, citing both superior performance and lower vulnerability risk.
Use it for
- High-throughput JSON serialization in data pipelines where encoding speed is a bottleneck.
- Web API responses requiring compact JSON output without pretty-printing overhead.
- Legacy codebases already using ujson that need continued support for newer Python versions.
- Applications requiring HTML-safe JSON encoding for embedded data in HTML contexts.
- Multi-threaded services where thread-safe JSON operations are needed without locking.
Worth the install?
AI-flagged interpretation of the facts on this page. Verify before relying on it.
Yes-with-conditions.
Install if you have an existing ujson dependency or need drop-in compatibility with code already using it. Do not install for new projects: the maintainers explicitly recommend orjson instead, citing both superior performance and lower architectural risk. The maintenance-only status and acknowledged security concerns make this suitable only for stable, low-change workloads.
Install
ujson on PyPI
Before you install
Medium install friction due to compiled C bindings requiring platform-specific wheels, but well-maintained with recent releases and broad platform coverage (macOS, Linux, Windows, multiple architectures). Actively maintained with support for current Python versions.
Requires Python 3.10 or later; compiled wheels available for common platforms but may require build tools on unsupported architectures.
License in practice
Dual-licensed under BSD-3-Clause and TCL (permissive licenses), imposing no restrictions on commercial or proprietary use.
Quickstart
pip install ujson
import ujson
ujson.dumps({"key": "value"})
ujson.loads('{"key": "value"}')Verify before relying
- Whether performance gains justify migration from standard json library for typical workloads (benchmarks show variability across test cases).
- Current security posture given maintenance-only status and known architectural limitations acknowledged in project documentation.
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 61 days since the last release |
| Last repo commit | |
| First released | |
| Downloads | 34,789,130 / month, #754 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 :: 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 |
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
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