Ultracite Rust-based linting/formatting (Biome). Use for project setup, Git hooks, migrations from ESLint/Prettier, or encountering configuration, monorepo, framework integration errors.
/plugin marketplace add secondsky/claude-skills/plugin install ultracite@claude-skillsThis skill inherits all available tools. When active, it can use any tool Claude has access to.
references/ai-editor-integration.mdreferences/biome.jsonc.monorepo.examplereferences/biome.jsonc.nextjs.examplereferences/biome.jsonc.react.examplereferences/biome.jsonc.svelte.examplereferences/biome.jsonc.vue.examplereferences/configuration-guide.mdreferences/git-hooks-setup.mdreferences/lefthook.yml.examplereferences/limitations-and-workarounds.mdreferences/lint-staged.config.examplereferences/migration-guides.mdreferences/monorepo-configuration.mdreferences/troubleshooting.mdscripts/install-ultracite.shscripts/migrate-to-ultracite.shFast, zero-config linting and formatting for modern JavaScript/TypeScript projects
Ultracite is a preset configuration built on Biome, a Rust-based linting and formatting toolchain. It provides a zero-configuration solution that replaces both ESLint and Prettier with a single, blazing-fast tool. Ultracite operates invisibly in the background, automatically formatting code and applying fixes on every save.
vs ESLint + Prettier:
vs Biome alone:
Use Ultracite when:
Limited framework support:
Specialized requirements:
Legacy projects:
For detailed limitations and workarounds, see: references/limitations-and-workarounds.md
When this skill is invoked, scan the project and assess:
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
Identify framework:
package.json for react, next, vue, svelte, etc.Assess project size:
Check TypeScript config:
tsconfig.json exists, note that Ultracite requires strictNullChecks: trueRecommend 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
package.json file in project root# Using Bun (preferred for speed)
bun x ultracite init
# Using npm
npx ultracite init
# Using pnpm
pnpm dlx ultracite init
# Using yarn
yarn dlx ultracite init
The interactive setup will:
biome.jsonc configuration.vscode/settings.json for editor integrationstrictNullChecks in tsconfig.json# Auto-detect settings, skip prompts
bunx ultracite init --quiet
# Specify options explicitly
bunx ultracite init \
--pm bun \
--frameworks react,next \
--editors vscode \
--agents cursor,claude \
--integrations husky \
--migrate eslint,prettier \
--quiet
Available flags:
--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)# 1. Install dependencies
bun add -D ultracite @biomejs/biome
# 2. Create biome.jsonc
cat > biome.jsonc << 'EOF'
{
"$schema": "https://biomejs.dev/schemas/2.3.8/schema.json",
"extends": ["ultracite/core"]
}
EOF
# 3. Create VS Code settings
mkdir -p .vscode
cat > .vscode/settings.json << 'EOF'
{
"editor.defaultFormatter": "biomejs.biome",
"editor.formatOnSave": true,
"editor.codeActionsOnSave": {
"quickfix.biome": "explicit",
"source.organizeImports.biome": "explicit"
}
}
EOF
# 4. Enable TypeScript strict mode
# Add to tsconfig.json:
{
"compilerOptions": {
"strictNullChecks": true
}
}
# Check installation
bunx ultracite doctor
# Expected output:
# ✔ Biome is installed
# ✔ Configuration file found: biome.jsonc
# ✔ Editor integration configured
# ✔ TypeScript strict mode enabled
File structure:
project-root/
├── biome.jsonc # Main configuration
├── .vscode/settings.json # VS Code integration
├── tsconfig.json # TypeScript config (strictNullChecks required)
└── package.json
Minimal biome.jsonc:
{
"$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
"files": {
"ignore": ["dist", "build", "coverage", "**/*.generated.ts"]
}
}
ultracite/react: React Hooks, JSX a11y, component best practicesultracite/nextjs: React + Next.js App Router, image optimization, document structureultracite/vue: Vue 3 Composition API, template syntax, reactivityultracite/svelte: Svelte 4/5 syntax, reactive declarationsUsage:
{
"extends": ["ultracite/core", "ultracite/react"]
}
The ultracite/core preset includes 200+ rules across 7 categories:
eval(), XSS risks, unsafe patternsconst preference, import organizationFormatting defaults: 2 spaces, 80 chars/line, LF endings, single quotes
For detailed framework presets, rule descriptions, and advanced configuration, see: references/configuration-guide.md
VS Code Setup:
biomejs.biome.vscode/settings.json:
{
"editor.defaultFormatter": "biomejs.biome",
"editor.formatOnSave": true,
"editor.codeActionsOnSave": {
"quickfix.biome": "explicit",
"source.organizeImports.biome": "explicit"
}
}
Features:
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"
}
}
Ultracite auto-detects and integrates with:
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
Ultracite generates AI editor rules that teach AI assistants about your linting/formatting standards.
Supported editors:
.cursorrules).windsurfrules).github/copilot-instructions.md).continuerules).codeiumrules).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
Ultracite optimizes for monorepos with:
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
Automatic migration:
bunx ultracite migrate eslint
bunx ultracite migrate prettier
bunx ultracite migrate biome
Manual migration:
biome.json with equivalent rulesFor complete migration guides with detailed rule mappings, see: references/migration-guides.md
CSS/SCSS: Biome does not lint CSS. Workaround: Use Stylelint
Framework gaps: Limited Angular/Astro support. Workaround: Use ultracite/core + manual rules
ESLint plugins: Many ESLint plugins have no Biome equivalent. Workaround: Run ESLint alongside Ultracite for specific plugins
File types: No Markdown, YAML, HTML linting. Workaround: Use dedicated tools (markdownlint, yamllint, htmlhint)
For complete list of limitations and detailed workarounds, see: references/limitations-and-workarounds.md
Common issues:
biome.jsonbunx instead of global installFor complete troubleshooting guide, see: references/troubleshooting.md
See scripts/install-ultracite.sh for automated setup.
See scripts/migrate-to-ultracite.sh for ESLint/Prettier migration.
See references/ directory for:
configuration-guide.md: Framework presets and rule detailsgit-hooks-setup.md: Husky, Lefthook, lint-staged setupai-editor-integration.md: Cursor, Claude Code, Copilot rulesmonorepo-configuration.md: Turborepo, Nx, pnpm workspacesmigration-guides.md: ESLint, Prettier, Biome migrationtroubleshooting.md: Common issues and solutionslimitations-and-workarounds.md: Known gaps and fixesCurrent versions (verified 2025-11-27):
ultracite: latest@biomejs/biome: >=1.9.0Check for updates:
npm view ultracite version
npm view @biomejs/biome version
Update:
bun update ultracite @biomejs/biome
Official Documentation:
Examples:
Troubleshooting:
Community:
Load reference files on-demand based on user questions or task requirements:
references/configuration-guide.md: When user asks about:
references/git-hooks-setup.md: When user asks about:
references/ai-editor-integration.md: When user asks about:
references/monorepo-configuration.md: When user asks about:
references/migration-guides.md: When user asks about:
references/troubleshooting.md: When user asks about:
references/limitations-and-workarounds.md: When user asks about:
Ultracite provides a zero-config, blazing-fast alternative to ESLint + Prettier:
✅ Use when:
⚠️ Consider alternatives when:
Key advantages:
Installation:
bun x ultracite init # Interactive setup
Most common workflow:
bun x ultracite initRemember:
strictNullChecks in TypeScript projectsThis skill should be used when the user asks to "create a slash command", "add a command", "write a custom command", "define command arguments", "use command frontmatter", "organize commands", "create command with file references", "interactive command", "use AskUserQuestion in command", or needs guidance on slash command structure, YAML frontmatter fields, dynamic arguments, bash execution in commands, user interaction patterns, or command development best practices for Claude Code.
This skill should be used when the user asks to "create an agent", "add an agent", "write a subagent", "agent frontmatter", "when to use description", "agent examples", "agent tools", "agent colors", "autonomous agent", or needs guidance on agent structure, system prompts, triggering conditions, or agent development best practices for Claude Code plugins.
This skill should be used when the user asks to "create a hook", "add a PreToolUse/PostToolUse/Stop hook", "validate tool use", "implement prompt-based hooks", "use ${CLAUDE_PLUGIN_ROOT}", "set up event-driven automation", "block dangerous commands", or mentions hook events (PreToolUse, PostToolUse, Stop, SubagentStop, SessionStart, SessionEnd, UserPromptSubmit, PreCompact, Notification). Provides comprehensive guidance for creating and implementing Claude Code plugin hooks with focus on advanced prompt-based hooks API.