Ultracite

Zero-config linting and formatting for JS/TS projects. Supports three linter backends: Biome (recommended), ESLint + Prettier, and Oxlint + Oxfmt.

Detecting Ultracite

Check if ultracite is in package.json devDependencies. Detect the active linter by looking for:

• biome.jsonc → Biome
• eslint.config.mjs → ESLint
• .oxlintrc.json → Oxlint

CLI Commands

# Check for issues (read-only)
bunx ultracite check

# Auto-fix issues
bunx ultracite fix

# Diagnose setup problems
bunx ultracite doctor

# Initialize in a new project
bunx ultracite init

Replace bunx with npx, pnpx, or yarn dlx depending on the package manager.

check and fix accept optional file paths: bunx ultracite check src/index.ts.

Initialization

bunx ultracite init runs an interactive setup. For non-interactive (CI) use, pass flags:

bunx ultracite init \
  --pm bun \
  --linter biome \
  --editors vscode cursor \
  --agents claude copilot \
  --frameworks react next \
  --integrations husky lint-staged \
  --quiet

Flags:

• --pm — npm | yarn | pnpm | bun
• --linter — biome (recommended) | eslint | oxlint
• --editors — vscode | zed | cursor | windsurf | antigravity | kiro | trae | void
• --agents — claude | codex | copilot | cline | amp | gemini | cursor-cli + 19 more
• --frameworks — react | next | solid | vue | svelte | qwik | remix | angular | astro | nestjs
• --integrations — husky | lefthook | lint-staged | pre-commit
• --hooks — Enable auto-fix hooks for supported agents/editors
• --type-aware — Enable type-aware linting (oxlint only)
• --skip-install — Skip dependency installation
• --quiet — Suppress prompts (auto-detected when CI=true)

Init creates config that extends Ultracite presets:

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

Framework presets available per linter: core, react, next, solid, vue, svelte, qwik, remix, angular, astro, nestjs.

Code Standards

When writing code in a project with Ultracite, follow these standards. For the full rules reference, see references/code-standards.md.

Key rules at a glance:

Formatting is handled by the project's configured linter/formatter. Respect the repository's existing formatter settings instead of forcing one fixed line width, quote style, or trailing comma policy.

Type safety: Use explicit types when they improve clarity. Prefer unknown over any. Use as const for immutable values and rely on type narrowing over blunt assertions.

Modern JavaScript/TypeScript: Prefer const, destructuring, optional chaining, nullish coalescing, template literals, for...of, and concise arrow functions.

Async and correctness: Always await promises in async functions. Prefer async/await over promise chains. Remove console.log, debugger, and alert from production code.

React and accessibility: Use function components, keep hooks top-level with correct deps, avoid nested component definitions, and use semantic HTML with the right labels, headings, alt text, and keyboard affordances.

Organization, security, performance, and testing: Keep functions focused, prefer early returns, avoid dangerouslySetInnerHTML and eval(), prefer specific imports and top-level regex, and keep tests free of .only and .skip.

Troubleshooting

Run bunx ultracite doctor to diagnose. It checks:

1. Linter installation (biome/eslint/oxlint binary available)
2. Config validity (extends ultracite presets correctly)
3. Ultracite in package.json dependencies
4. Conflicting tools (old .eslintrc.*, .prettierrc.* files)

Common fixes:

• Conflicting configs: Delete legacy .eslintrc.* and .prettierrc.* files after migrating to Ultracite
• Missing dependency: Run bunx ultracite init again or manually add ultracite to devDependencies
• Rules not applying: Ensure config file extends the correct presets for your framework