Ruff

Overview

Ruff brings Python linting and formatting together in a Rust-based tool, with automatic fixes for some violations. It is best suited to developers who can rely on its built-in rules and want one tool across editing and CI.

Its broad rule set and editor support make it a practical fit for routine Python quality checks; teams that need custom or third-party lint rules should choose another approach.

For category comparisons, see Linters and Code Formatting Tools.

Key features

Linting, security checks, and fixes

Ruff includes more than 900 built-in rules, including native implementations of popular Flake8 plugins. It can automatically fix lint violations such as unused imports, which reduces routine cleanup, though it does not promise a fix for every violation. A Bandit-derived rule group also detects common security issues, including possible vulnerabilities in Python code.

The central trade-off is a fixed rule set: Ruff does not support custom or third-party lint rules. That is a clear limitation for organizations enforcing house checks or relying on plugin rules beyond those built in. The maker describes Ruff as 10–100x faster than existing linters and formatters such as Flake8 and Black; that makes speed a notable part of its appeal, but it is not a guarantee for every project.

Formatting and editor workflow

Ruff’s formatter is designed as a drop-in replacement for Black. The FAQ allows for differences at the margins, so teams moving from Black should account for those rather than assume identical output. The built-in language server provides diagnostics, code actions for fixes, and formatting. For navigation and autocompletion, the documentation recommends pairing it with another Python language server.

Setup guides cover VS Code, Sublime Text, PyCharm, and Zed. In CI, Ruff documents GitHub Actions, GitLab CI/CD, and pre-commit hooks, making it usable both during editing and in automated checks. Configuration can live in pyproject.toml, ruff.toml, or .ruff.toml.

Installation and deployment

Developers can install Ruff with uv, pip, pipx, standalone installers, or package managers such as Homebrew and Conda. Astral also publishes a Docker image tagged by release, alongside a latest tag. That range suits local development and container-based workflows without changing Ruff’s built-in-rule constraint.

Pricing

Ruff is free: its open-source Python linter and formatter is permissively licensed. The Ruff plan costs nothing. There is no free trial because the tool is free rather than a time-limited offer, and no paid plan is needed to use the stated linting and formatting capabilities.

That makes it straightforward for individual developers and teams to adopt without a software subscription. The meaningful cost is instead the functional boundary: teams that require custom or third-party rules may need a different tool or workflow.

Platforms

Ruff supports Linux, macOS, and Windows, and is also listed for web and self-hosted use. Its editor integrations and CI options extend it into development and automation workflows, while its published Docker image supports containerized use.

Who it's for

Ruff is a strong choice for Python developers who want linting, formatting, security checks, and some automatic fixes in one free tool. It particularly suits projects whose checks fit Ruff’s built-in rules and teams that want editor and CI integration without a paid plan.

It is a weaker fit for teams that depend on organization-specific lint rules or third-party rules. Its language server also is not a complete replacement for Python navigation and autocompletion, which the documentation says should come from another language server.

Pros and cons

• Pros: More than 900 built-in rules and native implementations of popular Flake8 plugins cover a wide range of Python checks.
• Pros: Automatic fixes, including removal of unused imports, handle some recurring cleanup directly.
• Pros: The formatter, editor integrations, and CI hooks let teams use Ruff across local editing and automated checks.
• Pros: The free, permissively licensed plan avoids a subscription cost.
• Cons: No custom or third-party lint rules means teams cannot extend Ruff for specialized checks.
• Cons: The formatter may differ from Black at the margins, so replacement does not guarantee identical formatting.
• Cons: The language server needs a companion Python language server for navigation and autocompletion.
• Cons: Editor setup help is provided on a best-effort basis, with assistance directed through issue reports.

Alternatives

Choose Biome if you need a free, open-source toolchain for web projects rather than Ruff’s Python-focused linting and formatting.

Astral is another free option from the same maker, grouping Ruff with uv and ty; choose it when you want that broader set of Astral tools rather than Ruff alone.

PMD is a free, downloadable static code analyzer; consider it when that analyzer form better fits your needs.

golangci-lint is a free, open-source project built by volunteers; choose it when that project is the better fit for your linting needs.

Stylelint is a free alternative for readers considering another linting tool.

ESLint is a free, open-source JavaScript linting utility; choose it for JavaScript rather than Python.

detekt is a free open-source Kotlin static analysis tool, making it the relevant option for Kotlin code.

ShellCheck is another free alternative for readers looking beyond Python tooling.

Verdict

Choose Ruff for a free, integrated Python linter and formatter when its built-in rules cover your needs. Its breadth, automatic fixes, editor support, and CI integrations make it a persuasive everyday option; look elsewhere if custom or third-party lint rules are essential.