Ruff

This is your go-to for Python linting and formatting. Ruff replaces Black, Flake8, isort, and a bunch of other tools with one extremely fast binary. The skill covers when to use it (look for tool.ruff in pyproject.toml), how to invoke it through uv or uvx, and includes the key commands you'll actually need. One smart callout: it warns you not to format an entire unformatted codebase just because you touched one file, which is the kind of practical advice that saves PR headaches. Also explains unsafe fixes, which is important since some auto-fixes can change behavior, not just style. If you're working with modern Python projects, you're going to see ruff everywhere.