ruff check: Fast Linting Command Reference

Lint a Python codebase in milliseconds.

ruff check runs a fast Rust-based linter over your code, reporting style and correctness issues. Its speed makes it ideal as an early, cheap CI gate.

Common flags / usage

• ruff check . -- lint the whole tree
• --fix -- auto-fix violations that are safe to fix
• --no-fix -- report only, never modify (CI default)
• --output-format=github -- emit GitHub Actions annotations
• --select / --ignore RULES -- tune the active rule set

Example

- run: pip install ruff
- run: ruff check --output-format=github .

In CI

Run ruff check without --fix in CI so it fails on violations instead of silently rewriting code. --output-format=github turns findings into inline PR annotations. Pair with "ruff format --check" to enforce formatting too.

Key takeaways

• ruff check is a very fast linter, good as an early CI gate.
• Use --output-format=github for inline PR annotations.
• Keep --fix out of CI so violations fail rather than auto-rewrite.

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