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/