Ruff Linter & Formatter
Lint and format your Python code online with Ruff — the extremely fast Rust-based linter that replaces Flake8, isort and Black.
Why use this tool?
Use this when you want to lint or auto-format Python without installing anything. Ruff is the fast, modern replacement for Flake8, isort, pyupgrade, and Black, and here it runs entirely in your browser via WebAssembly — paste code, pick your rules or format settings, and get results instantly.
Lint results will appear here.
About Ruff Linter & Formatter
Ruff has become the de-facto standard for Python linting and formatting because it is written in Rust and runs 10–100× faster than the tools it replaces. A single tool covers what previously required Flake8 (and dozens of its plugins), isort, pyupgrade, autoflake, and the Black formatter.
This online version runs the official Ruff WebAssembly build directly in your browser — there is no server, no upload, and no installation. Linting reports each issue with its rule code (for example F401 for an unused import or E701 for multiple statements on one line), its exact line and column, and whether Ruff can auto-fix it.
Switch to Format mode to reformat your code to a consistent style with configurable line length and quote preference, matching what `ruff format` would produce in your editor or CI. Choose a rule preset — from Ruff's default set to the full ALL ruleset — to control how strict the linting is.
Frequently Asked Questions
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