Ultracite

Ultracite Skill

Fast, zero-config linting and formatting for modern JavaScript/TypeScript projects

Overview

Ultracite is a unified linting and formatting solution that supports multiple providers: Biome (default, Rust-based), ESLint+Prettier+Stylelint, and Oxlint+Oxfmt. It provides framework-specific presets and zero-configuration defaults, replacing traditional ESLint+Prettier setups with a faster, simpler alternative. Ultracite operates invisibly in the background, automatically formatting code and applying fixes on every save.

Version 7 Changes: Multi-provider architecture, preset path migration, MCP server support, AI hooks Version 6 Changes: Framework-specific presets introduced (React, Next.js, Vue, Svelte, etc.)

Core Goals

1. Lightning-Fast Performance: Leverages Biome's Rust implementation for instant linting/formatting
2. Zero-Config Design: Ships with 200+ sensible defaults optimized for modern TypeScript development
3. Simplicity & Invisibility: Operates with minimal user interaction
4. Type Safety: Enforces TypeScript strict mode and comprehensive null/undefined handling
5. Tool Compatibility: Works alongside other development tools without conflicts

Key Benefits vs Alternatives

vs ESLint + Prettier:

• 10-100x faster performance (Rust vs JavaScript)
• Single tool instead of two
• Zero configuration needed
• Auto-fixes on save by default
• Built-in TypeScript strict mode

vs Biome alone:

• 200+ preconfigured rules
• Framework-specific presets (React, Next.js, Vue, Svelte)
• AI editor integration (Cursor, Claude Code, Copilot)
• Git hook integrations
• Migration tooling

When to Use This Skill

✅ Ideal Projects

Use Ultracite when:

• Starting a new JavaScript/TypeScript project
• Building with React, Next.js, Vue, Svelte, or other modern frameworks
• Working in monorepos (Turborepo, Nx, Lerna)
• Teams want consistent formatting without bikeshedding
• Performance is critical (large codebases, CI/CD optimization)
• Migrating from ESLint + Prettier to a faster solution
• Using AI coding assistants (Cursor, Claude Code, Windsurf)
• TypeScript projects requiring strict type safety
• Projects with accessibility requirements (ARIA, semantic HTML)

⚠️ Consider Alternatives When

Limited framework support:

• Need Angular/Ember-specific rules (Biome support is basic)
• Require advanced CSS linting (Stylelint still recommended)

Specialized requirements:

• Need specific ESLint plugins not replicated in Biome
• Require property ordering in CSS (Stylelint feature)
• Team has extensive custom ESLint configurations

Legacy projects:

• Large codebases with custom ESLint rules (migration effort required)
• Projects with extensive Prettier customization

For detailed limitations and workarounds, see: references/limitations-and-workarounds.md

Interactive Components

This skill provides interactive commands and autonomous agents for streamlined workflows:

Commands

• /ultracite:doctor - Validate project setup, check for v6→v7 preset paths, detect conflicts
• /ultracite:migrate - Interactive migration wizard (ESLint/Prettier → Ultracite, v6→v7 upgrade)

Agents

• config-validator - Analyze biome.jsonc for syntax, preset paths, rule conflicts, performance
• migration-assistant - Guide ESLint/Prettier migrations with rule mapping and gap analysis

See README.md for complete interactive features documentation.

Choosing a Provider

Ultracite v7 supports three linting providers. Choose based on your needs:

🚀 Biome (Default) - Recommended for most projects

• Speed: Fastest (10-100x faster than ESLint)
• Setup: Zero-config with 200+ preset rules
• Best for: New projects, TypeScript-first development, performance-critical builds
• Limitations: Fewer rules than ESLint, basic CSS/SCSS support

🔧 ESLint + Prettier + Stylelint - Recommended for maximum compatibility

• Speed: Slower but mature ecosystem
• Setup: Requires more configuration
• Best for: Projects with existing ESLint plugins, advanced CSS/SCSS linting needs
• Limitations: JavaScript-based (slower), requires multiple tools

⚡ Oxlint + Oxfmt - Recommended for maximum speed

• Speed: Fastest linting (even faster than Biome for linting only)
• Setup: Type-aware linting with TypeScript integration
• Best for: Large TypeScript codebases, type-safety-critical projects
• Limitations: Newer ecosystem, fewer rules than ESLint

Provider selection during init:

bun x ultracite init --linter biome   # Default
bun x ultracite init --linter eslint  # ESLint + Prettier + Stylelint
bun x ultracite init --linter oxlint  # Oxlint + Oxfmt

Load provider-specific documentation:

• Biome: references/provider-biome.md
• ESLint: references/provider-eslint.md
• Oxlint: references/provider-oxlint.md

Version Migration Guide

Upgrading from v6 to v7

Breaking Change: Preset paths have changed in v7.

v6 paths (old):

{
  "extends": ["ultracite/core", "ultracite/react"]
}

v7 paths (new):

{
  "extends": ["ultracite/biome/core", "ultracite/biome/react"]
}

Migration steps:

1. Update ultracite package: bun update ultracite
2. Update preset paths in biome.jsonc (add /biome/ segment)
3. Run npx ultracite doctor to validate configuration
4. Test linting: npx ultracite check .

New v7 features:

• Multi-provider support (Biome, ESLint, Oxlint)
• MCP server integration for AI assistants
• AI hooks (auto-format after AI edits)
• Type-aware linting (Oxlint)
• ultracite doctor diagnostics command

Load full v7 migration guide: references/v7-migration.md

Upgrading from v5 to v6

Key Change: Framework-specific presets introduced.

v5 approach (old):

{
  "extends": ["ultracite/core"]
}

v6 approach (new):

{
  "extends": ["ultracite/core", "ultracite/react"]  // Framework preset
}

Load full v6 migration guide: references/v6-migration.md

Project Suitability Assessment

When this skill is invoked, scan the project and assess:

1. Check existing tooling:

   # Check for ESLint
   ls -la .eslintrc* eslint.config.* package.json | grep eslint
   
   # Check for Prettier
   ls -la .prettierrc* prettier.config.* package.json | grep prettier
   
   # Check for Biome
   ls -la biome.json* package.json | grep biome

2. Identify framework:

   • Check package.json for react, next, vue, svelte, etc.
   • Recommend appropriate preset

3. Assess project size:

   • Large projects (1000+ files) benefit most from Rust performance
   • Small projects may not notice speed difference

4. Check TypeScript config:

   • If tsconfig.json exists, note that Ultracite requires strictNullChecks: true
   • Warn if disabled (will generate many warnings)

5. Recommend or warn:

   ✅ RECOMMENDED: This TypeScript + React project is ideal for Ultracite
   - 500+ files will benefit from Rust performance
   - React preset available
   - Can replace existing ESLint + Prettier setup
   
   ⚠️ CONSIDER: This project uses advanced ESLint plugins
   - Custom rule: eslint-plugin-custom-security
   - May need to retain ESLint for these specific rules
   - Could use Ultracite for formatting only

Installation & Setup

Prerequisites

• Node.js v20+
• Package manager: Bun (preferred), npm, pnpm, or yarn
• package.json file in project root

Quick Start (Interactive)

# Using Bun (preferred for speed)
bun x ultracite init

# With provider selection (v7+)
bun x ultracite init --linter biome   # Default, fastest
bun x ultracite init --linter eslint  # ESLint + Prettier + Stylelint
bun x ultracite init --linter oxlint  # Oxlint + Oxfmt (type-aware)

# Using npm
npx ultracite init

# Using pnpm
pnpm dlx ultracite init

# Using yarn
yarn dlx ultracite init

The interactive setup will:

1. Prompt for provider selection (Biome, ESLint, Oxlint) - v7+ only
2. Install Ultracite and provider dependencies
3. Prompt for framework selection (React, Next.js, Vue, etc.)
4. Ask about editor setup (VS Code, Cursor, etc.)
5. Offer AI agent rules installation (Cursor, Claude Code, Copilot)
6. Prompt for Git hook integration (Husky, Lefthook, lint-staged)
7. Offer to migrate from existing tools (ESLint, Prettier)
8. Create/merge configuration file (biome.jsonc, .eslintrc.js, etc.)
9. Update .vscode/settings.json for editor integration
10. Enable strictNullChecks in tsconfig.json (if TypeScript)

Non-Interactive Setup (CI/Automation)

# Auto-detect settings, skip prompts
bunx ultracite init --quiet

# Specify options explicitly (v7+)
bunx ultracite init \
  --linter biome \
  --pm bun \
  --frameworks react,next \
  --editors vscode \
  --agents cursor,claude \
  --integrations husky \
  --migrate eslint,prettier \
  --quiet

Available flags:

• --linter: Provider selection (biome, eslint, oxlint) - v7+ only
• --pm: Package manager (bun, npm, pnpm, yarn)
• --frameworks: react, next, solid, vue, qwik, angular, remix, svelte
• --editors: vscode, zed
• --agents: cursor, claude, cline, copilot, windsurf, etc.
• --integrations: husky, lefthook, lint-staged
• --migrate: eslint, prettier, biome
• --quiet: Skip all prompts (auto-enabled when CI=true)

Manual Setup (Advanced)

# 1. Install dependencies
bun add -D ultracite@7 @biomejs/biome@^2.0.0

# 2. Create biome.jsonc
cat > biome.jsonc << 'EOF'
{
  "$schema": "https://biomejs.dev/schemas/2.3.8/schema.json",
  "extends": ["ultracite/core"]
}
EOF

# 3. Create VS Code settings
mkdir -p .vscode
cat > .vscode/settings.json << 'EOF'
{
  "editor.defaultFormatter": "biomejs.biome",
  "editor.formatOnSave": true,
  "editor.codeActionsOnSave": {
    "quickfix.biome": "explicit",
    "source.organizeImports.biome": "explicit"
  }
}
EOF

# 4. Enable TypeScript strict mode
# Add to tsconfig.json:
{
  "compilerOptions": {
    "strictNullChecks": true
  }
}

Verify Installation

# Check installation
bunx ultracite doctor

# Expected output:
# ✔ Biome is installed
# ✔ Configuration file found: biome.jsonc
# ✔ Editor integration configured
# ✔ TypeScript strict mode enabled

Configuration

Basic Configuration

File structure:

project-root/
├── biome.jsonc              # Main configuration
├── .vscode/settings.json    # VS Code integration
├── tsconfig.json            # TypeScript config (strictNullChecks required)
└── package.json

Minimal biome.jsonc:

{
  "$schema": "https://biomejs.dev/schemas/2.3.8/schema.json",
  "extends": ["ultracite/core"],

  // Optional: Add framework preset
  // "extends": ["ultracite/core", "ultracite/react"],

  // Optional: Customize rules
  "linter": {
    "rules": {
      "suspicious": {
        "noConsoleLog": "off"  // Disable specific rule
      }
    }
  },

  // Optional: Exclude files (Biome 2.x: use `includes` with `!` negation)
  "files": {
    "includes": ["**", "!dist", "!build", "!coverage", "!**/*.generated.ts"]
  }
}

Framework Presets

• ultracite/react: React Hooks, JSX a11y, component best practices
• ultracite/nextjs: React + Next.js App Router, image optimization, document structure
• ultracite/vue: Vue 3 Composition API, template syntax, reactivity
• ultracite/svelte: Svelte 4/5 syntax, reactive declarations

Usage:

{
  "extends": ["ultracite/core", "ultracite/react"]
}

Core Preset

The ultracite/core preset includes 200+ rules across 7 categories:

• Accessibility: ARIA validation, semantic HTML, keyboard navigation
• Correctness: Type safety, unused code removal, exhaustive dependencies
• Performance: Code optimization, barrel file warnings
• Security: Prevents eval(), XSS risks, unsafe patterns
• Style: Consistent patterns, const preference, import organization
• Suspicious: Catches loose equality, debugger statements, typos
• Complexity: Cognitive complexity limits

Formatting defaults: 2 spaces, 80 chars/line, LF endings, single quotes

For detailed framework presets, rule descriptions, and advanced configuration, see: references/configuration-guide.md

Usage

IDE Integration (Recommended)

VS Code Setup:

1. Install Biome extension: biomejs.biome
2. Verify .vscode/settings.json:

   {
     "editor.defaultFormatter": "biomejs.biome",
     "editor.formatOnSave": true,
     "editor.codeActionsOnSave": {
       "quickfix.biome": "explicit",
       "source.organizeImports.biome": "explicit"
     }
   }

3. Disable conflicting extensions (ESLint, Prettier)

Features:

• Auto-format on save
• Auto-fix on save (removes unused imports, fixes order, applies strict equality)
• Format on paste
• Problems panel for unfixable issues
• Quick fixes via lightbulb indicators

CLI Usage

Check code (lint only):

bunx ultracite check
bunx ultracite check src/
bunx ultracite check --diagnostic-level error  # Only errors

Fix code (auto-fix):

bunx ultracite check --write
bunx ultracite check --write src/

Format code (format only):

bunx ultracite format --write
bunx ultracite format --write src/

Package.json scripts:

{
  "scripts": {
    "lint": "ultracite check",
    "lint:fix": "ultracite check --write",
    "format": "ultracite format --write"
  }
}

Git Hook Integrations

Ultracite auto-detects and integrates with:

• Husky: Node.js-based hook manager
• Lefthook: Fast Go-based hook manager
• lint-staged: Runs linters on staged files only

Quick setup:

# Husky
bunx ultracite init --integrations husky

# Lefthook
bunx ultracite init --integrations lefthook

# lint-staged
bunx ultracite init --integrations lint-staged

Example .husky/pre-commit:

#!/usr/bin/env sh
. "$(dirname -- "$0")/_/husky.sh"

ultracite check --staged --write

For complete Git hook setup guides (Husky, Lefthook, lint-staged), see: references/git-hooks-setup.md

AI Editor Rules

Ultracite generates AI editor rules that teach AI assistants about your linting/formatting standards.

Supported editors:

• Cursor (.cursorrules)
• Claude Code (.windsurfrules)
• GitHub Copilot (.github/copilot-instructions.md)
• Continue.dev (.continuerules)
• Codeium (.codeiumrules)
• Zed (.zedrules)

Generate rules:

bunx ultracite generate-ai-rules
bunx ultracite generate-ai-rules --all  # All editors
bunx ultracite generate-ai-rules --editor=cursor  # Specific editor

For complete AI editor integration guide and customization, see: references/ai-editor-integration.md

Monorepo Support

Ultracite optimizes for monorepos with:

• Shared base configurations
• Package-specific overrides
• Turborepo/Nx caching integration
• Performance optimization for large workspaces

Example monorepo structure:

monorepo/
├── biome.json              # Shared base config
├── apps/
│   └── web/
│       └── biome.json      # Next.js-specific overrides
└── packages/
    └── ui/
        └── biome.json      # React-specific overrides

For complete monorepo setup, Turborepo/Nx integration, and performance tips, see: references/monorepo-configuration.md