Essential Lint Rules
Not every lint rule earns its CI time. These rule sets catch real bugs and style drift with minimal false positives for Python 3.14 projects.
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Not every lint rule earns its CI time. These rule sets catch real bugs and style drift with minimal false positives for Python 3.14 projects.
[tool.ruff.lint]
select = ["E", "F", "I", "UP", "B", "SIM", "RUF", "S", "T20"]
ignore = ["E501", "S101"] # line length via formatter; assert ok in testsWhen to reach for this:
# Violations caught by essential rules:
import os, sys # I: unsorted imports
x = 1 # F841: unused variable (F)
eval("1+1") # S307: dangerous eval (S)
print("debug") # T20: print statement (T20)
class unused: ... # F: defined but never useduv run ruff check example.py
# I001 Import block is un-sorted
# F841 Local variable `x` is assigned but never used
# S307 Use of possibly insecure function
# T201 `print` foundWhat this demonstrates:
I catches import disorder before reviewF catches dead code and undefined namesS (bandit) flags security anti-patternsT20 catches leftover debug prints| Tier | Rules | Purpose |
|---|---|---|
| Core | E, F, I, UP | Style, bugs, imports, syntax upgrades |
| Quality | B, SIM, RUF | Bugbear, simplification, ruff-specific |
| Security | S (bandit) | SQL injection, eval, hardcoded secrets |
| Hygiene | T20, PT | No print in prod; pytest best practices |
[tool.ruff.lint.per-file-ignores]
"tests/**" = ["S101"] # allow assert in tests
"migrations/**" = ["E", "F"] # skip lint on Django migrationsselect = ["ALL"]) - hundreds of false positives. Fix: start with the core set; add rules incrementally.assert. Fix: per-file ignore for tests/**.target-version to requires-python.scripts/ or CLI entry points.| Alternative | Use When | Don't Use When |
|---|---|---|
| Minimal (E, F only) | Very early prototype | Production code |
| Full ALL | Security-critical systems | Small teams without lint budget |
| pylint | Deep analysis | Speed-critical CI |
At minimum: E, F, I, UP. Add B and SIM for quality, S for security-sensitive code.
ruff rule B006 prints the rule description and examples.
Ruff has flake8-type-checking (TCH) rules. Useful but can be noisy. Prefer mypy/pyright for types.
Enable new rules, run ruff check --fix, commit fixes, then add to CI.
Ruff-native rules for patterns other plugins miss (ambiguous Unicode, invalid pyproject.toml).
Yes. Allow assert (S101), print for debugging, and magic values (PLR2004) in tests.
Add to ignore = ["RULE"] in [tool.ruff.lint].
No in ruff. They are fast and high-value for web apps and CLIs handling user input.
Enable DJ (flake8-django) for Django projects. Skip for FastAPI/Flask.
When upgrading ruff. Review the changelog for new high-value rules each quarter.
Stack versions: This page was written for Python 3.14.0, FastAPI 0.115+, Django 5.2, Flask 3.1, Pydantic 2, PyTorch 2.6+, pandas 2.2+, Polars 1.x, ruff 0.9+, and uv 0.6+.
Reviewed by Chris St. John·Last updated Jul 19, 2026