Python Formatter
FormattersFormat Python code with Ruff WASM — Black-compatible, line width 88, double quotes, magic trailing comma. Instant, browser-based, no installation needed.
About Python Formatter
The Python Formatter is a Ruff WASM-powered, browser-based tool that instantly formats Python source code to Black-compatible style. Using a WebAssembly port of the Ruff formatter (the fastest Python linter and formatter) running in a Web Worker, it applies a default line width of 88 columns (Black's default), double-quote string normalisation, magic trailing comma preservation, and PEP 8-compliant indentation. The result is identical to running `ruff format` or `black` locally — without any installation. Your code never leaves the browser.
Features
- ✓Powered by Ruff WASM — a WebAssembly port of the fastest Python formatter available
- ✓Black-compatible output — identical results to running `black` on the same file
- ✓Configurable indent width: 2 spaces, 4 spaces (PEP 8 default), or tab
- ✓Line width of 88 columns (Black default) for consistent wrapping
- ✓Double-quote string normalisation (configurable in ruff_fmt internals)
- ✓Magic trailing comma: respected — trailing commas prevent line-merging
- ✓Formats dataclasses, decorators, type hints (PEP 484/526/604), and walrus operator
- ✓Web Worker execution — WASM runs off the main thread, UI stays responsive
- ✓Syntax-highlighted editor for both input and output
- ✓One-click clipboard copy of formatted output
- ✓Real-time byte-savings stats (input vs output size)
- ✓Language picker — instantly switch to Go, Java, Bash, or 20+ other formatters
- ✓Mobile-responsive layout with a dedicated Format button
- ✓100% client-side — your code never leaves the browser
Common Use Cases
- Formatting Python scripts and modules to Black style before committing
- Checking how Black would reformat a snippet without installing it
- Normalising function signatures, dataclass definitions, and type hints
- Cleaning up auto-generated or AI-produced Python code
- Preparing PEP 8-compliant Python snippets for documentation or tutorials
- Standardising formatting across a Python monorepo or library
Frequently Asked Questions
QIs this the same as running Black?
Yes — Ruff's formatter is designed to be a drop-in replacement for Black and produces byte-for-byte identical output in the vast majority of cases. It respects the same conventions: 88-column lines, double quotes, trailing commas.
QWhat Python versions and syntax are supported?
Python 3.8 through 3.13 — including match/case (pattern matching), walrus operator (:=), PEP 604 union types (X | Y), type aliases (type X = ...), and all modern type hint syntax.
QIs my code sent to a server?
No. The Ruff WASM binary runs entirely inside your browser in a Web Worker. No code is transmitted to any server.
QCan I change the line length or quote style?
The default configuration matches Black (line width 88, double quotes, magic trailing comma respected). Advanced configuration options are not yet exposed in the UI.