ruff

Ruff Cursor Rules

You are an expert in Ruff Python linting and formatting. Follow these rules:

Configuration

• Configure in pyproject.toml [tool.ruff] or standalone ruff.toml — not both
• Set target-version = "py312" (or your minimum Python version) explicitly
• Set line-length = 88 (Black default) or 120 — be explicit, don't rely on default
• Use src = ["src"] to help Ruff resolve first-party imports correctly

Rule Selection

• Start with select = ["E", "F", "W", "I", "UP", "B", "SIM", "N"] for a solid baseline
• Add "S" (bandit) for security, "PT" for pytest style, "D" for docstrings as needed
• Use ignore sparingly and document why: ignore = ["E501"] # handled by formatter
• Use per-file-ignores for test/migration exceptions: {"tests/" = ["S101"], "migrations/" = ["E501"]}

Formatting

• Use ruff format as a drop-in Black replacement — same output, faster
• Don't mix Ruff formatter with Black — pick one
• Set format.quote-style = "double" and format.indent-style = "space" explicitly
• Use ruff check --fix && ruff format for the standard fix-then-format workflow

Import Sorting

• Enable isort rules with "I" in select — Ruff replaces isort entirely
• Configure [tool.ruff.isort] for known-first-party, known-third-party if needed
• Use force-single-line = true if your team prefers one import per line
• Set combine-as-imports = true to group aliased imports

Integration

• Run in CI: ruff check . && ruff format --check .
• Use --fix only in local development, never in CI (CI should fail, not auto-fix)
• Pre-commit hook: use ruff-pre-commit (official) — not generic pre-commit hooks
• VS Code: install charliermarsh.ruff extension, disable pylint/flake8/isort extensions

Noqa & Suppression

• Use inline # noqa: RULE_CODE with specific codes — never bare # noqa
• Use per-file-ignores over blanket noqa comments when an entire file needs exceptions
• Run ruff check --statistics to see which rules fire most — fix patterns, not symptoms