nox-without-uv-backend

What it flags

Flags repositories and CI jobs that use nox without the --uv flag or nox.options.uv = True.

nox can delegate virtualenv creation and package installation to uv with one flag or config line, speeding up session setup significantly.

Why it matters

nox’s default backend uses virtualenv and pip, which are slower than uv equivalents. Passing --uv or setting nox.options.uv = True transparently swaps in uv, accelerating all session environment creation and dependency installation.

Current heuristic

The rule looks for:

• a repository with nox usage (noxfile.py or nox references in config files)
• a CI step that runs nox without --uv
• (workflow rule only) per-job detection of nox commands missing --uv

The rule intentionally skips:

• nox commands that already include --uv
• repositories that have nox.options.uv = True in noxfile.py
• repositories without visible nox usage

When to ignore it

Ignore this finding when:

• the project relies on pip-specific behavior that uv does not replicate
• the team has intentionally kept the pip backend for consistency
• certain nox sessions require virtualenv features that uv does not support

Suggested verification

• Run the same nox sessions with and without --uv
• Compare session setup wall-clock time
• Verify that test output and environment behavior remain identical

Sources

• https://nox.thea.codes/en/stable/config.html#opt-in-uv-backend
• https://docs.astral.sh/uv/guides/integration/