Oxfmt — The Oxc Formatter

Oxfmt is a Prettier-compatible formatter for the JavaScript ecosystem. It currently passes ~95% of Prettier's JS/TS test suite. It formats JavaScript, JSX, TypeScript, TSX, JSON, JSONC, JSON5, YAML, TOML, HTML, Angular, Vue, CSS, SCSS, Less, Markdown, MDX, GraphQL, Ember, and Handlebars.

When to use oxfmt

• After modifying code in a project that has oxfmt installed
• Setting up formatting in a new JS/TS project
• Migrating from Prettier to oxfmt
• Configuring formatting rules, editor integration, or CI checks

Quick reference

Installation

# Pick your package manager
npm add -D oxfmt
pnpm add -D oxfmt
yarn add -D oxfmt
bun add -D oxfmt

Add scripts to package.json:

{
  "scripts": {
    "fmt": "oxfmt",
    "fmt:check": "oxfmt --check"
  }
}

Running oxfmt with no arguments formats the current directory (like prettier --write .).

CLI flags

Flag	Purpose
--check	Check formatting without writing (exit 1 if unformatted)
--list-different	List files that would change
--write	Format and write in place (default)
--init	Create .oxfmtrc.json with defaults
--migrate=prettier	Convert .prettierrc to .oxfmtrc.json
--migrate=biome	Convert Biome config to .oxfmtrc.json
-c PATH	Use a specific config file
--ignore-path PATH	Custom ignore file (repeatable)
--with-node-modules	Include node_modules/ (skipped by default)
--no-error-on-unmatched-pattern	Don't fail on unmatched globs
--stdin-filepath PATH	Format stdin, using PATH to infer parser
--threads N	Thread count (set to 1 for single core)
--lsp	Start the LSP server (used by editors)

CLI does not support formatting options as flags (e.g., no --no-semi). Use the config file instead — this keeps formatting consistent across CLI, editors, and CI.

Configuration

Oxfmt looks for .oxfmtrc.json or .oxfmtrc.jsonc starting from the current directory, walking up.

Generate a starter config:

oxfmt --init

Core options

{
  "$schema": "./node_modules/oxfmt/configuration_schema.json",
  "printWidth": 100,       // Line width limit (default: 100, Prettier default is 80)
  "tabWidth": 2,           // Spaces per indent level
  "useTabs": false,        // Tabs vs spaces
  "semi": true,            // Semicolons
  "singleQuote": false,    // Quote style
  "trailingComma": "all",  // Trailing commas in multi-line
  "insertFinalNewline": true
}

Note: oxfmt defaults printWidth to 100, while Prettier defaults to 80. If migrating, decide which you prefer.

Per-file overrides

{
  "printWidth": 100,
  "overrides": [
    {
      "files": ["*.test.js", "*.spec.ts"],
      "options": { "printWidth": 120 }
    },
    {
      "files": ["*.json"],
      "excludeFiles": ["package.json"],
      "options": { "tabWidth": 4 }
    }
  ]
}

Built-in features

These are disabled by default but can be enabled in the config:

• sortImports — Sorts import statements
• sortTailwindcss — Sorts Tailwind CSS classes
• sortPackageJson — Sorts package.json fields (enabled by default)

Ignore patterns

Add ignorePatterns in the config file, or use a .oxfmtignore / .prettierignore file:

{
  "ignorePatterns": ["dist/", "coverage/", "*.min.js"]
}

.editorconfig support

Oxfmt reads these .editorconfig properties (nearest file only, no merging):

• end_of_line → endOfLine
• indent_style → useTabs
• indent_size → tabWidth
• max_line_length → printWidth
• insert_final_newline → insertFinalNewline

Migrating from Prettier

# Install oxfmt
pnpm add -D oxfmt

# Auto-convert .prettierrc → .oxfmtrc.json
oxfmt --migrate=prettier

# Format everything so the diff is clean
pnpm oxfmt

# Replace Prettier scripts in package.json
# "prettier --write ."  → "oxfmt"
# "prettier --check ."  → "oxfmt --check"

After migration, review the generated .oxfmtrc.json — especially printWidth since the default changed from 80 to 100.

Editor integration

Editor extensions use the local oxfmt --lsp, so oxfmt must be installed in the project.

VS Code / Cursor: Install the "Oxc" extension from the VS Code Marketplace. Recommended team setup:

.vscode/extensions.json:

{ "recommendations": ["oxc.oxc-vscode"] }

.vscode/settings.json:

{
  "editor.defaultFormatter": "oxc.oxc-vscode",
  "editor.formatOnSave": true
}

Zed: Install the oxc extension from Zed's marketplace.

JetBrains (IntelliJ / WebStorm): Install from JetBrains Marketplace.

Neovim:

• With nvim-lspconfig: npm i -g oxfmt then vim.lsp.enable('oxfmt')
• With conform.nvim: set formatters_by_ft for js/ts/json/vue
• With coc.nvim: :CocInstall coc-oxc

Other LSP-compatible editors (Emacs, Helix, Sublime): Point at oxfmt --lsp.

Non-LSP editors: Pipe via stdin: cat file.js | oxfmt --stdin-filepath file.js

CI setup

GitHub Actions:

jobs:
  format:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v6
      - uses: pnpm/action-setup@v4
      - uses: actions/setup-node@v6
        with:
          node-version: lts/*
          cache: pnpm
      - run: pnpm install --frozen-lockfile
      - run: pnpm run fmt:check

GitLab CI:

oxfmt:
  image: node:lts
  stage: test
  before_script:
    - npm install
  script:
    - npm run fmt:check

Autofix (GitHub): Use autofix.ci — run oxfmt (no --check) and let the action commit fixes.

Pre-commit hook (lint-staged)

{
  "lint-staged": {
    "*": "oxfmt --no-error-on-unmatched-pattern"
  }
}

Use --no-error-on-unmatched-pattern so non-supported file types don't cause errors.

Node.js API

import { format } from "oxfmt";

const result = format("foo.ts", "const   x:string   =   1", {
  semi: false,
  singleQuote: true,
});
console.log(result); // const x: string = 1

Workflow after code changes

When you've modified files in an oxfmt-enabled project:

1. Run pnpm oxfmt (or the project's fmt script) to format changed files
2. If in CI or a check context, use --check instead to verify without writing

The formatter is fast enough to run on the entire project — no need to target individual files unless piping via stdin.