tox-without-tox-uv

What it flags

Flags jobs that run tox without tox-uv installed.

tox-uv is a plugin that replaces tox’s default virtual environment creation and package installation with uv’s resolver and installer. It requires no configuration changes and is auto-discovered when installed alongside tox.

Why it matters

tox’s default venv creation uses the virtualenv package and pip for installation, which can be slower than uv equivalents. The tox-uv plugin transparently swaps these out for uv’s faster implementations, speeding up tox runs with no workflow changes.

Current heuristic

The rule looks for:

• a step that runs tox (e.g., tox, tox run, python -m tox)
• no step in the same job that installs tox-uv (e.g., pip install tox-uv)
• detection is per-job; if a job installs tox-uv before running tox, it is not flagged

The rule intentionally skips:

• jobs that already install tox-uv in any step
• workflows where tox is not used

When to ignore it

Ignore this finding when:

• tox-uv is installed through a composite action or reusable workflow that the linter cannot see
• the job uses a custom tox environment that relies on pip-specific behavior
• the team has intentionally kept the pip-based workflow for consistency across environments

Suggested verification

• Run the same tox environments with and without tox-uv installed
• Compare total job wall-clock time, especially for projects with many tox environments or heavy dependencies
• Verify that test output and environment behavior remain identical

Sources

• https://github.com/tox-dev/tox-uv
• https://docs.astral.sh/uv/guides/integration/