What is the difference between flake8 and Ruff?

Flake8 is a Python-based linter that delegates to PyFlakes, pycodestyle, and mccabe. Ruff is a Rust-based linter that reimplements flake8's entire rule set (plus many popular plugins) with autofix support and runs 10-100x faster. Ruff also bundles formatting and import sorting.

Should I use flake8 or Ruff?

For new projects, Ruff is the better default: it covers flake8's rules, adds autofix, and runs much faster. Existing projects with a tuned flake8 configuration and plugin stack can keep using flake8, but migrating to Ruff is straightforward since it maps each flake8 rule code to an equivalent.

Does flake8 support pyproject.toml?

No. Flake8 reads configuration from setup.cfg, tox.ini, or a dedicated .flake8 file. It does not natively support pyproject.toml, though the third-party flake8-pyproject plugin adds that capability.

flake8: Python Linter

by Tim Hopper

Flake8 is a Python linting tool that wraps three checkers into one CLI: PyFlakes for logical errors, pycodestyle for PEP 8 style, and mccabe for cyclomatic complexity. A plugin system extends it with additional rules.

Ruff reimplements flake8’s entire rule set with autofix support and 10-100x faster runs. Consider Ruff for new projects.

When to use flake8

Flake8 fits codebases that already run it in CI and have tuned a stable configuration across setup.cfg, tox.ini, or .flake8. Teams that depend on flake8 plugins without Ruff equivalents, or that have built pre-commit hooks and editor integrations around its output, keep a familiar tool backed by a long-running ecosystem.

For new projects, Ruff implements flake8’s rule set (plus many popular plugins) with autofix support and faster runs. See How do Ruff and Pylint compare? for an evaluation of the modern alternatives, or How to replace Black, isort, flake8, and pyupgrade with Ruff for a step-by-step migration that maps each flake8 plugin to its Ruff prefix.

Key Features

Code analysis

Flake8 delegates error detection to PyFlakes, which flags undefined names, unused imports, redefined-but-unused variables, and other logical problems without executing the code. The mccabe checker reports functions whose cyclomatic complexity exceeds a configurable threshold.

Style enforcement

The pycodestyle checker validates PEP 8 compliance: line length, whitespace around operators, blank-line conventions, and import ordering. Each violation gets a code (e.g. E501 for long lines, W291 for trailing whitespace) that can be individually suppressed or enforced.

Configuration

Flake8 reads configuration from setup.cfg, tox.ini, or a dedicated .flake8 file. It does not natively read pyproject.toml. Rules can be toggled globally with --select and --ignore, or suppressed per line with # noqa: E501.

Plugins

A plugin ecosystem adds checks beyond the built-in set. Popular plugins include flake8-bugbear (additional opinionated warnings), flake8-import-order, and flake8-docstrings. Ruff reimplements most of these as built-in rule prefixes, which is one of the main reasons projects migrate.

Pros

Combined PyFlakes, pycodestyle, and mccabe checks in a single invocation
Large plugin ecosystem for specialized rules
Per-line suppression with # noqa codes
Stable rule codes that have not changed in years

Cons

No autofix: reports problems but does not rewrite code
10-100x slower than Ruff on large codebases
No native pyproject.toml support
No formatting capabilities (requires pairing with Black or Ruff)

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Last updated on May 22, 2026

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