Ultracite Documentation

Ultracite provides opinionated presets for three major toolchains. You can choose the one that best fits your project's performance and ecosystem requirements:

• Biome: A modern, all-in-one toolchain written in Rust.
• ESLint + Prettier + Stylelint: The most mature and comprehensive linting ecosystem.
• Oxlint + Oxfmt: The fastest linter available, optimized for speed (50-100x faster than ESLint).

Ultracite is a preset configuration (a curated bundle of rules and settings) that sits on top of an existing toolchain. It is not a standalone linter or formatter engine.

• The Engine: Tools like Biome, ESLint + Prettier + Stylelint, or Oxlint + Oxfmt perform the actual linting and formatting.
• The Configuration: Ultracite provides the ready-to-go rulesets for these engines to save you from manual configuration.

To prevent noisy CI results, the regression gate compares a head build against a base build interleaved on the same runner. A provider or command is flagged as a regression only if it meets both of the following criteria:

1. Effect Size: The head/base median ratio is greater than BENCH_REGRESSION_RATIO (default 1.25, meaning >25% slower).
2. Significance: A one-sided Mann–Whitney U test results in p < BENCH_ALPHA (default 0.05).

If you do not want to use the CLI for initialization, you can manually import and extend Ultracite's published configuration presets. Supported presets include:

• Biome
• ESLint
• Oxlint
• Oxfmt
• Prettier
• Stylelint

Refer to the official documentation at https://ultracite.ai/ for exact import paths and extension points.

Ultracite provides a dedicated tanstack framework preset that integrates Biome, ESLint, and Oxlint.

• ESLint: Layers @tanstack/eslint-plugin-query, @tanstack/eslint-plugin-router, and @tanstack/eslint-plugin-start.
• Biome & Oxlint: Automatically relaxes file-naming conventions for routes/ directories and the generated routeTree.gen.ts files.

Note for existing users (v7.8.0+):

• TanStack Query rules have moved from the react preset to the tanstack preset. If your project relies on these rules, you must explicitly opt into the tanstack preset.
• TanStack Router projects now automatically resolve to the tanstack preset instead of the remix preset.

If you are moving from an existing linting or formatting configuration, Ultracite provides specific step-by-step migration guides for the following tools:

• ESLint
• Prettier
• Stylelint
• Biome
• Oxlint

If you require full control over the migration process, follow these steps:

1. Follow the standard Setup steps to install Ultracite.
2. Manually remove Prettier and any related dependencies from your project.
3. Manually delete your Prettier configuration files (e.g., .prettierrc, prettier.config.js).
4. Restart your editor to ensure the new configuration is applied.

To switch your project to the ESLint ecosystem, run the initialization command with the eslint linter flag. This will generate eslint.config.mjs, prettier.config.mjs, and stylelint.config.mjs files using the ultracite/eslint/ preset paths.

npx ultracite init --linter eslint

Adhere to these modern syntax patterns:

• Use arrow functions for callbacks and short functions.
• Prefer for...of loops over .forEach() or indexed for loops.
• Use optional chaining (?.) and nullish coalescing (??) for safe property access.
• Use template literals instead of string concatenation.
• Use destructuring for object and array assignments.
• Use const by default; use let only when reassignment is required; never use var.

In version 7.9.3, all JS-plugin-based rules (such as eslint-plugin-github, eslint-plugin-sonarjs, and oxlint-plugin-react-doctor) were moved from the core and framework presets into a single opt-in preset: ultracite/oxlint/js-plugins.

To use these rules, you must manually install the underlying plugins and extend the new preset alongside your chosen core and framework preset. This ensures that the core, react, next, and tanstack presets run exclusively on Oxlint's native Rust rules for maximum performance.

Steps to enable JS plugins:

1. Install eslint-plugin-github, eslint-plugin-sonarjs, and oxlint-plugin-react-doctor as devDependencies.
2. Extend ultracite/oxlint/js-plugins in your configuration.

To use Ultracite's Prettier configuration, create a prettier.config.mjs file. The configuration includes prettier-plugin-tailwindcss by default. If you use Astro or Svelte, their respective plugins will be inserted before the Tailwind plugin.

import config from "ultracite/prettier";

export default {
  ...config,
  plugins: ["prettier-plugin-tailwindcss"],
};