Formatter from Bun
If you’ve worked in the modern JavaScript/TypeScript ecosystem, formatting your codebase with Prettier has likely become standard practice. But as projects grow to tens or hundreds of thousands of files, code formatting quickly becomes a bottleneck in local pre-commit hooks and CI pipelines.
Enter bun fmt—Bun’s fast, zero-config built-in code formatter designed to replace Prettier without breaking your workflow.
What is Bun?
Bun is a fast, all-in-one JavaScript and TypeScript toolkit designed as a modern alternative to Node.js and Deno.
Rather than just being a runtime to execute JavaScript code, Bun replaces multiple fragmented tools in the JavaScript ecosystem with a single, high-performance tool written in Rust
Why bun fmt Changes the Game
1. Mind-Blowing Performance (Up to 320x Faster)
Running Prettier across a massive codebase can take minutes. bun fmt cuts that down to split seconds:
| Formatter | Time (--check on ~10,000 files) |
Speedup vs. Prettier |
|---|---|---|
| Bun fmt | 0.43 s | 320× faster |
| oxfmt | 0.85 s | 2× slower than Bun |
| Biome | 3.6 s | 8.3× slower than Bun |
| Prettier | 139 s | Baseline |
2. 5x Memory Efficiency
While Prettier consumes nearly 1 GB of RAM (approx. 972 MB) on large codebases, bun fmt completes the same check using just 183 MB. That means lighter CI runners, lower cloud bills, and zero lagging on local dev environments.
3. 99% Prettier Test Parity Out-of-the-Box
Switching formatters usually means fighting Git diff wars across your entire engineering team. bun fmt mitigates this by passing 9,728 out of 9,821 (99%) of Prettier’s test suite. Your output remains consistent, clean, and Prettier-compatible without requiring massive refactoring.
Broad Language & Syntax Support
bun fmt handles 20 languages and formats right out of the box, covering virtually every file type in a full-stack project:
JavaScript & TypeScript (JS, TS, JSX, TSX, Flow)
Web Languages (HTML, CSS, SCSS, Less)
Frontend Frameworks (Vue, Angular, Handlebars)
Data Formats (JSON, JSONC, JSON5, YAML, TOML, GraphQL)
Content Formats (Markdown, MDX, MJML)
Zero Config Required (Works with Existing .prettierrc)
bun fmt works without extra setup. If you already have a .prettierrc or .oxfmtrc.json in your repository, bun fmt reads it natively.
To customize options or set overrides, configure the [fmt] section in your bunfig.toml:
# bunfig.toml
[fmt]
printWidth = 100
semi = false
singleQuote = true
sortImports = true # Automatically sorts imports
# Set overrides for specific files
[[fmt.overrides]]
files = ["*.test.ts", "scripts/**"]
options = { printWidth = 120 }
How to Use bun fmt
Format Your Project
Run bun fmt in your terminal to automatically format all non-ignored files:
bun fmt
Check Formatting in CI
Use --check to fail if any files require formatting:
bun fmt --check
Instant Pre-Commit Hooks (No lint-staged Needed)
Format staged Git files directly before committing:
bun fmt --staged
Sort imports
You can sort the imports
[fmt]
sortImports = true
Imports are grouped: built-in modules, packages, aliases like
@/, relative paths, styles.Each group is sorted by path, and the names in
{ }are sorted too.Two imports from the same module become one.
Side-effect imports like
import "./setup"never move, and nothing moves past one.
To pick your own groups, use a table. See format.sortImports
[fmt.sortImports]
groups = ["react", "builtin", "external", "internal", ["parent", "sibling", "index"]]
customGroups = [{ groupName = "react", elementNamePattern = ["react", "react-dom/**"] }]
Sort Tailwind CSS classes
[fmt]
sortTailwindcss = true
Classes are sorted in Tailwind's recommended order, in class and className and in calls to clsx, cn, cva, twMerge, and a few more. They are sorted with your project's tailwindcss, version 3 or 4, and are left as they are if it isn't installed.
If your .prettierrc lists prettier-plugin-tailwindcss, sorting is already on, with that plugin's options and defaults.
To name your own functions or your stylesheet, use a table.
[fmt.sortTailwindcss]
stylesheet = "./src/app.css"
functions = ["clsx", "tw"]
How to Migrate in 10 Seconds
If you’re currently using Prettier in your package.json, update your script to use bun fmt:
{
"scripts": {
"format": "bun fmt"
}
}
To know more about how to migrate from Prettier and oxfmt to bun fmt read the posts from Bun
Migrate from Prettier to bun fmt - https://bun.com/guides/format/migrate-from-prettier
Migrate from oxfmt to bunfmt - https://bun.com/guides/format/migrate-from-oxfmt
