---name: ultracitedescription: Ultracite is a zero-config linting and formatting preset for JavaScript/TypeScript projects. Use when: (1) Setting up or initializing Ultracite in a project (ultracite init), (2) Running linting or formatting commands (check, fix, doctor), (3) Writing or reviewing JS/TS code in a project that uses Ultracite — to follow its code standards, (4) Troubleshooting linting/formatting issues, (5) User mentions 'ultracite', 'lint', 'format', 'code quality', or 'biome/eslint/oxlint' in a project with Ultracite installed.---

Ultracite

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

Detecting Ultracite

Check if ultracite is in package.json dependencies or devDependencies. Detect the active linter by looking for (searching upward from the current directory):

• biome.json / biome.jsonc → Biome
• eslint.config.* (.mjs, .js, .cjs, .ts, .mts, .cts) → ESLint (with Prettier for formatting)
• oxlint.config.ts → Oxlint (with oxfmt.config.ts for formatting)

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, pnpm exec, or yarn depending on the package manager, so the project's installed Ultracite runs (pnpm dlx and yarn dlx download the latest release instead, and Yarn 1 has no dlx). Only init in a project without Ultracite needs a download runner such as pnpm dlx.

check and fix accept optional file paths: bunx ultracite check src/index.ts. Unknown options are passed through to the underlying linter (e.g. bunx ultracite check --max-warnings 0).

Initialization

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

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

Flags:

• --pm — npm | yarn | pnpm | bun | deno | nub | aube
• --linter — oxlint (recommended) | biome | eslint
• --editors — universal (writes .vscode/settings.json for every VS Code-based editor) | vscode | cursor | windsurf | codebuddy | antigravity | bob | kiro | trae | void | zed
• --agents — universal (writes AGENTS.md) | claude | codex | copilot | cline | amp | gemini | cursor-cli + 34 more (41 agents supported)
• --frameworks — react | next | solid | vue | svelte | qwik | remix | tanstack | angular | astro | nestjs | jest | vitest
• --integrations — husky | lefthook | lint-staged | pre-commit
• --hooks — Enable auto-fix hooks: claude | copilot | cursor | windsurf | codebuddy
• --js-plugins — Opt-in Oxlint JS plugins: @shadcn/lint | anti-slop | eslint-plugin-github | eslint-plugin-sonarjs | oxlint-plugin-react-doctor
• --type-aware — Enable type-aware linting (Biome: extends the type-aware preset; Oxlint: installs oxlint-tsgolint)
• --install-skill — Install the reusable Ultracite skill after setup
• --skip-install — Skip dependency installation
• --quiet — Suppress prompts (auto-detected when CI=true); defaults to oxlint when --linter is omitted

Init creates config that extends Ultracite presets:

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

// eslint.config.mjs — arrays of flat configs, spread together
import core from "ultracite/eslint/core";
import react from "ultracite/eslint/react";
export default [...core, ...react];

// oxlint.config.ts — imports passed to extends
import { defineConfig } from "oxlint";
import core from "ultracite/oxlint/core";
export default defineConfig({
  extends: [core],
  ignorePatterns: core.ignorePatterns,
});

Presets available per linter (ultracite/<linter>/<preset>): core, react, next, solid, vue, svelte, qwik, remix, tanstack, angular, astro, nestjs, jest, vitest. Biome also has type-aware. Oxlint also has js-plugins (eslint-plugin-github, eslint-plugin-sonarjs and oxlint-plugin-react-doctor run through oxlint's JS plugin support, with next/js-plugins and tanstack/js-plugins adding framework-specific React Doctor rules), anti-slop and shadcn. These are opt-in: init only adds them when picked in its prompt or passed with --js-plugins.

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 and formatter installation (Biome; or ESLint + Prettier + Stylelint; or Oxlint + oxfmt)
2. Config validity (extends the ultracite presets correctly)
3. Ultracite in package.json dependencies
4. Conflicting tools (legacy .eslintrc.* files; .prettierrc.*/prettier.config.* when not using the ESLint backend)

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