Biome Tooling

Biome is a modern, performant toolchain for JavaScript, TypeScript, and related web languages. It combines formatting, linting, and import organization into a single tool that's 15-20x faster than ESLint/Prettier.

When to Use This Skill

Use this skill when...	Use another approach when...
Starting a new JS/TS project	Need specific ESLint plugins (React hooks, a11y)
Want zero-config formatting/linting	Have complex custom ESLint rules
Need fast CI/CD pipelines	Need framework-specific rules (Next.js, Nuxt)
Migrating from ESLint+Prettier	Legacy codebase with heavy ESLint customization

Hybrid approach: Use Biome for formatting, ESLint for specialized linting.

Core Expertise

What is Biome?

• All-in-one toolchain: Linter + formatter + import sorter
• Zero-config: Works out of the box with sensible defaults
• Fast: Written in Rust, processes files in parallel
• Compatible: Matches Prettier formatting 97%+
• Supports: JavaScript, TypeScript, JSX, TSX, JSON, CSS

Installation

# Project-local (recommended)
bun add --dev @biomejs/biome

# Verify installation
bunx biome --version

# Initialize configuration
bunx biome init

Essential Commands

# Format files
bunx biome format --write src/

# Lint with fixes
bunx biome lint --write src/

# Check everything (format + lint + organize imports)
bunx biome check --write src/

# Check without changes (CI mode)
bunx biome check src/

# CI mode (exits with error on issues)
bunx biome ci src/

# Migrate from ESLint/Prettier
bunx biome migrate eslint --write
bunx biome migrate prettier --write

# Explain a rule
bunx biome explain noUnusedVariables

Configuration (biome.json)

Minimal Setup (Zero Config)

Biome works without configuration. For basic customization:

{
  "$schema": "https://biomejs.dev/schemas/1.9.4/schema.json",
  "vcs": {
    "enabled": true,
    "clientKind": "git",
    "useIgnoreFile": true
  },
  "files": {
    "ignoreUnknown": false,
    "ignore": ["dist", "build", "node_modules", ".next", "coverage"]
  },
  "formatter": {
    "enabled": true,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 100
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true
    }
  },
  "organizeImports": {
    "enabled": true
  }
}

Rule Categories

Category	Purpose	Example Rules
recommended	Essential rules everyone should enable	Most rules marked "recommended"
correctness	Prevent bugs and logic errors	noUnusedVariables, noUnreachable
suspicious	Detect code that might be wrong	noExplicitAny, noDoubleEquals
style	Enforce consistent style	useConst, noVar
complexity	Reduce code complexity	noForEach, useFlatMap
performance	Optimize performance	noAccumulatingSpread
a11y	Accessibility best practices	noSvgWithoutTitle, useAltText
security	Security vulnerabilities	noDangerouslySetInnerHtml

Common Patterns

Ignore Files and Directories

Via biome.json:

{
  "files": {
    "ignore": [
      "dist",
      "build",
      "node_modules",
      "**/*.config.js",
      "scripts/legacy/**"
    ]
  }
}

Via .gitignore (automatic):

{
  "vcs": {
    "enabled": true,
    "useIgnoreFile": true
  }
}

Performance Comparison

Tool	Time (1000 files)	Notes
Biome	0.5s	Rust, parallel processing
ESLint	8-10s	Node.js, single-threaded
Prettier	3-5s	Node.js, formatting only
ESLint + Prettier	11-15s	Sequential execution

Agentic Optimizations

Context	Command
Quick check	bunx biome check src/
Fix all	bunx biome check --write src/
Format only	bunx biome format --write src/
Lint only	bunx biome lint --write src/
CI mode	bunx biome ci src/
Errors only	bunx biome check --diagnostic-level=error src/
Limited output	bunx biome check --max-diagnostics=10 src/
GitHub reporter	bunx biome check --reporter=github src/
JSON output	bunx biome check --reporter=json src/
Migrate ESLint	bunx biome migrate eslint --write
Migrate Prettier	bunx biome migrate prettier --write

Quick Reference

Flag	Description
--write	Apply fixes/formatting
--reporter=github	GitHub annotations format
--reporter=json	JSON output
--diagnostic-level=error	Errors only
--max-diagnostics=N	Limit output count
--verbose	Show detailed diagnostics
--no-errors-on-unmatched	Ignore unmatched files
ci	CI mode (check + exit code)

For detailed examples, advanced patterns, and best practices, see REFERENCE.md.

References

• Official docs: https://biomejs.dev
• Configuration: https://biomejs.dev/reference/configuration/
• Rules: https://biomejs.dev/linter/
• Migration guide: https://biomejs.dev/guides/migrate-eslint-prettier/
• Editor integration: https://biomejs.dev/