Migrate from ESLint

If you're using ESLint and want to switch to Ultracite's preconfigured setup, this guide will help you migrate while maintaining code quality standards.

Why Migrate to Ultracite?

• Lightning Speed: Biome (Ultracite's foundation) is based on Rust, much faster than ESLint
• Zero Configuration: Hundreds of preconfigured rules vs manual ESLint setup
• Combined Tool: Replaces both ESLint and Prettier with a single tool
• AI Integration: Built-in support for AI-powered editors (Cursor, Windsurf, GitHub Copilot)
• Type Safety: Comprehensive TypeScript rules with strict null checks
• Modern Standards: Latest JavaScript/TypeScript best practices

Before You Start

Make sure you have:

• An existing project using ESLint
• Node.js v14.18+ (Node 18+ recommended)
• A package.json file

Migration Steps

1. Remove ESLint Dependencies

Remove ESLint and related packages from your project:

npm uninstall $(npm ls --depth=0 --json | jq -r '.dependencies | keys[]' | grep eslint)

This command will remove all dependencies containing the word "eslint" i.e. plugins, presets, etc.

2. Remove ESLint Configuration Files

Delete your existing ESLint configuration files. These might include:

• .eslintrc.js
• .eslintrc.json
• .eslintrc.yml
• .eslintignore
• eslint.config.js

etc.

3. Update VS Code Settings

If you have ESLint configured in your .vscode/settings.json, remove any references to it. For example, you might have configuration like this:

{
  "eslint.format.enable": true,
  "editor.codeActionsOnSave": {
    "source.fixAll.eslint": true
  }
}

4. Install Ultracite

Run the automatic setup script.

npx ultracite init

This will:

• Install Ultracite as a dependency
• Merge your existing biome.json / biome.jsonc with Ultracite's preset
• Merge your existing .vscode/settings.json with Ultracite's preset
• Enable strictNullChecks in your tsconfig.json file (or create one if it doesn't exist)
• Preserve your custom rules and settings
• Set up editor integrations

Following the upgrade, you may want to review your biome.json / biome.jsonc file to remove any overrides. Additionally, restart your editor to ensure the new configuration is applied.

5. Update scripts in package.json

If you have ESLint related scripts in your package.json, you can replace them with Ultracite equivalents. For example, you might want scripts like this:

{
  "scripts": {
    "lint": "npx ultracite@latest lint",
    "format": "npx ultracite@latest format"
  }
}

Your project should now be running with Ultracite's fast, comprehensive linting and formatting!