Are We Biome Yet?

A CLI tool to analyze your ESLint configuration and determine compatibility with Biome, the fast formatter and linter written in Rust.

What it does

This tool helps you migrate from ESLint to Biome by:

1. Analyzing your ESLint config - Reads your ESLint configuration files and extracts the rules you're using
2. Mapping to Biome equivalents - Cross-references your ESLint rules with Biome's available rules using the official Biome rules metadata
3. Providing compatibility report - Shows which rules have Biome equivalents and which don't
4. Calculating migration readiness - Gives you a percentage of how ready your config is for Biome migration

Usage

Or run directly with:

npx are-we-biome-yet

Usage

Basic Analysis

# Analyze current directory
are-we-biome-yet .

# Analyze specific path
are-we-biome-yet /path/to/your/file.js

# Output as JSON for programmatic use
are-we-biome-yet . --json

Example Output

🔍 Analyzing ESLint configuration...

Found 15 ESLint rules in your configuration

✅ Compatible with Biome (13 rules):
  • no-unused-vars → noUnusedVariables (javascript/complexity)
  • no-console → noConsole (javascript/suspicious)
  • prefer-const → useConst (javascript/style)
  • no-var → noVar (javascript/style)
  • semi → useSemicolons (javascript/style)
  • quotes → useSingleQuote (javascript/style)
  • indent → useIndent (javascript/style)
  • comma-dangle → useTrailingCommas (javascript/style)
  • no-trailing-spaces → noTrailingSpaces (javascript/style)
  • eol-last → useNewlineAtEndOfFile (javascript/style)
  • no-multiple-empty-lines → noMultipleEmptyLines (javascript/style)
  • no-tabs → noTabs (javascript/style)
  • no-debugger → noDebugger (javascript/suspicious)

❌ No Biome equivalent (2 rules):
  • @typescript-eslint/no-explicit-any
  • react-hooks/exhaustive-deps

📊 Compatibility: 86.67% (13/15 rules)

Development

Prerequisites

• Node.js 18+
• Bun (for package management)

Setup

1. Clone the repository

   git clone https://github.com/your-username/are-we-biome-yet.git
   cd are-we-biome-yet

2. Install dependencies

   bun install

3. Build the project

   bun run build

Project Structure

are-we-biome-yet/
├── src/
│   ├── commands/
│   │   ├── analyze.ts    # Main analysis logic
│   │   └── biome.ts      # Biome rules fetching and mapping
│   ├── utils/
│   │   └── logger.ts     # Logging utilities
│   └── index.ts          # CLI entry point
├── biome.json            # Biome configuration
├── package.json          # Dependencies and scripts
├── tsup.config.ts        # Build configuration
└── tsconfig.json         # TypeScript configuration

Key Components

src/commands/analyze.ts

• Parses ESLint configuration files
• Extracts rules from various ESLint config formats
• Orchestrates the analysis process

src/commands/biome.ts

• Fetches Biome rules metadata from https://biomejs.dev/metadata/rules.json
• Maps ESLint rules to Biome equivalents
• Identifies Biome-exclusive rules

src/utils/logger.ts

• Provides consistent logging across the application
• Supports different log levels and output formats

Development Commands

# Build the project
bun run build

# Run in development mode
bun run dev

# Run tests
bun run test

# Lint with Biome
bun run lint

# Format with Biome
bun run format

# Type check
bun run typecheck

Adding New Features

1. New Commands: Add new command files in src/commands/
2. Rule Mappings: The Biome rules are automatically fetched from the official metadata endpoint
3. Configuration Parsers: Extend the ESLint config parsing in analyze.ts

Testing

# Run tests
bun run test

# Run tests in watch mode
bun run test:watch

Contributing

1. Fork the repository
2. Create a feature branch: git checkout -b feature/amazing-feature
3. Make your changes
4. Run tests and linting: bun run test && bun run lint
5. Commit your changes: git commit -m 'Add amazing feature'
6. Push to the branch: git push origin feature/amazing-feature
7. Open a Pull Request

How it Works

1. ESLint Configuration Parsing

The tool supports multiple ESLint configuration formats:

• .eslintrc.js
• .eslintrc.json
• .eslintrc.yaml
• eslint.config.js (flat config)
• package.json eslint field

2. Rule Extraction

Extracts rules from:

• Direct rule configurations
• Extended configurations (like eslint:recommended)
• Plugin rules (with proper prefix handling)

3. Biome Rule Mapping

• Fetches the latest Biome rules from the official metadata endpoint
• Maps ESLint rules to Biome equivalents based on the sources field
• Handles plugin prefixes (e.g., @typescript-eslint/ → base rule name)

4. Compatibility Analysis

• Calculates which rules have Biome equivalents
• Provides detailed mapping information
• Shows compatibility percentage

License

MIT License - see LICENSE file for details.

Acknowledgments

• Biome team for the excellent tool and metadata API
• ESLint community for the comprehensive linting ecosystem