Nox
Nox is a free, open-source command-line tool for automating tests across multiple Python environments.
What Nox is
Nox is a free, open-source command-line tool for automating tests across multiple Python environments. Projects define sessions in a standard Python file called `noxfile.py`. For each session, Nox can create a virtual environment, install specified dependencies, and run commands in sequence. Sessions can target different Python interpreters, each with a separate environment, and can be parameterized to vary dependency or database values. Environment backends include venv, uv, conda, mamba, micromamba, and virtualenv. Tags help organize sessions and choose which ones to run. Nox also provides helpers for loading dependencies from `pyproject.toml` files and PEP 723 scripts. It runs on Linux, macOS, and Windows and can be installed with pip or pipx. For CI, its tutorial documents use of the wntrblm/nox GitHub Action to install Nox and select Python versions. The project describes its scope as Python testing and recommends other tools for broader task-execution needs. Its homepage says more than 3,000 projects use Nox.
Good
- Free and open-source
- Runs sessions across multiple Python interpreters
- Supports six environment backends
- Session tags help select work to run
- Available on Linux, macOS, and Windows
Watch out
- Specialized for Python testing
- Recommends other tools for broader task execution
Who it suits
Nox suits developers who want to define and run Python test sessions across interpreters and environment managers. It is focused on Python testing rather than broader task execution.
Verdict
Nox offers configurable, repeatable sessions for Python testing across interpreters and environment backends. Its stated focus is testing, so projects seeking a broader task runner may want a different tool.
Plans and prices
From Nox's own pricing page, checked 9 Oct 2026.
| Plan | Price | What it gives you |
|---|---|---|
| Nox | Free | Free and open-source software |
The facts
Each one read from Nox's own pages, with the date it was checked.
What it does
- CI integration
- The tutorial documents using the wntrblm/nox GitHub Action to install Nox and select Python versions.checked 9 Oct 2026
- Configuration
- Nox uses a standard Python file named noxfile.py for project configuration.checked 9 Oct 2026
- Environment backends
- Nox supports venv, uv, conda, mamba, micromamba, and virtualenv backends.checked 9 Oct 2026
- Environment setup
- For each session, Nox can create a virtual environment, install specified dependencies, and run commands in order.checked 9 Oct 2026
- Installation
- Nox can be installed with pip or pipx.checked 9 Oct 2026
- Maintainers
- The project lists community maintainers and contributors and says it pays contributors through Open Collective.checked 9 Oct 2026
- Multiple interpreters
- A session can run against multiple Python interpreters, with a separate virtual environment for each interpreter.checked 9 Oct 2026
- Project adoption
- The homepage says more than 3,000 projects use Nox.checked 9 Oct 2026
- Purpose
- Nox is a command-line tool that automates testing in multiple Python environments.checked 9 Oct 2026
- Python project helpers
- Nox provides helpers to load dependencies from pyproject.toml files and PEP 723 scripts.checked 9 Oct 2026
- Scope
- The project describes Nox as specialized for Python testing and recommends other tools for broader task execution needs.checked 9 Oct 2026
- Session parameters
- Sessions can be parameterized to run with different dependency or database values.checked 9 Oct 2026
- Session tags
- Sessions can be organized and selected using tags.checked 9 Oct 2026
