Ultracite

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

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, pnpx, or yarn dlx depending on the package manager.

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
• --linter — biome (recommended) | eslint | oxlint
• --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
• --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)

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 github and sonarjs (ESLint plugins run via oxlint's JS plugin support, included by default on init).

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