Biome Tooling

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

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

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

Agentic Optimizations

Quick Reference

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/

Biome Tooling - Reference

Detailed reference material for Biome formatter and linter.

Recommended Production Setup

{
  "$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", ".nuxt", "coverage"]
  },
  "formatter": {
    "enabled": true,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 100,
    "lineEnding": "lf"
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true,
      "suspicious": {
        "noExplicitAny": "error",
        "noConsoleLog": "warn"
      },
      "style": {
        "noNonNullAssertion": "warn",
        "useConst": "error"
      },
      "correctness": {
        "noUnusedVariables": "error",
        "noUnusedImports": "error"
      },
      "complexity": {
        "noForEach": "off"
      }
    }
  },
  "organizeImports": {
    "enabled": true
  },
  "javascript": {
    "formatter": {
      "quoteStyle": "single",
      "trailingCommas": "all",
      "semicolons": "asNeeded",
      "arrowParentheses": "asNeeded"
    }
  },
  "overrides": [
    {
      "include": ["*.test.ts", "*.spec.ts"],
      "linter": {
        "rules": {
          "suspicious": {
            "noExplicitAny": "off"
          }
        }
      }
    }
  ]
}

Editor Integration

VS Code

Install extension:

code --install-extension biomejs.biome

Settings (.vscode/settings.json):

{
  "[javascript]": {
    "editor.defaultFormatter": "biomejs.biome",
    "editor.formatOnSave": true,
    "editor.codeActionsOnSave": {
      "quickfix.biome": "explicit",
      "source.organizeImports.biome": "explicit"
    }
  },
  "[typescript]": {
    "editor.defaultFormatter": "biomejs.biome",
    "editor.formatOnSave": true,
    "editor.codeActionsOnSave": {
      "quickfix.biome": "explicit",
      "source.organizeImports.biome": "explicit"
    }
  },
  "[json]": {
    "editor.defaultFormatter": "biomejs.biome",
    "editor.formatOnSave": true
  }
}

Neovim (with nvim-lspconfig)

-- Using mason and lspconfig
require('lspconfig').biome.setup({
  cmd = { 'biome', 'lsp-proxy' },
  filetypes = {
    'javascript',
    'typescript',
    'javascriptreact',
    'typescriptreact',
    'json',
    'jsonc',
  },
  root_dir = require('lspconfig.util').root_pattern(
    'biome.json',
    'biome.jsonc'
  ),
  single_file_support = false,
  on_attach = function(client, bufnr)
    -- Format on save
    vim.api.nvim_create_autocmd('BufWritePre', {
      buffer = bufnr,
      callback = function()
        vim.lsp.buf.format({ async = false })
      end,
    })
  end,
})

JetBrains IDEs

• Settings > Plugins > Search "Biome" > Install
• Settings > Languages & Frameworks > Biome
• Enable "Run Biome on save"
• Set Biome executable path

Pre-commit Hook Setup

Using Husky + lint-staged:

# Install dependencies
bun add --dev husky lint-staged

# Initialize husky
bunx husky init

package.json:

{
  "scripts": {
    "prepare": "husky"
  },
  "lint-staged": {
    "*.{js,ts,jsx,tsx,json}": [
      "biome check --write --no-errors-on-unmatched"
    ]
  }
}

.husky/pre-commit:

#!/usr/bin/env sh
bunx lint-staged

Using pre-commit (Python):

# .pre-commit-config.yaml
repos:
  - repo: https://github.com/biomejs/pre-commit
    rev: v0.1.0
    hooks:
      - id: biome-check
        additional_dependencies: ["@biomejs/biome@1.9.4"]

CI/CD Integration

GitHub Actions

name: Biome Check
on:
  push:
    branches: [main]
  pull_request:

jobs:
  biome:
    name: Format & Lint
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4

      - uses: oven-sh/setup-bun@v2
        with:
          bun-version: latest

      - name: Install dependencies
        run: bun install --frozen-lockfile

      - name: Run Biome
        run: bunx biome ci src/

GitLab CI

biome:
  image: oven/bun:latest
  stage: test
  script:
    - bun install --frozen-lockfile
    - bunx biome ci src/
  only:
    - merge_requests
    - main

Migration Strategies

From ESLint + Prettier

# 1. Remove old tools
bun remove eslint prettier eslint-config-prettier

# 2. Delete config files
rm .eslintrc.json .prettierrc .prettierignore

# 3. Install Biome
bun add --dev @biomejs/biome

# 4. Initialize configuration
bunx biome init

# 5. Migrate rules (optional)
bunx biome migrate eslint --write
bunx biome migrate prettier --write

# 6. Format entire codebase
bunx biome check --write src/

# 7. Update scripts in package.json
{
  "scripts": {
    "format": "biome format --write src/",
    "lint": "biome lint --write src/",
    "check": "biome check --write src/",
    "ci": "biome ci src/"
  }
}

Gradual Migration (Keep Both)

{
  "scripts": {
    "format": "biome format --write src/ && prettier --write 'docs/**/*.md'",
    "lint": "biome lint --write src/ && eslint --fix 'legacy/**/*.js'"
  }
}

Use Biome for new code, keep old tools for legacy directories.

Rule-Specific Overrides

{
  "overrides": [
    {
      "include": ["*.test.ts", "*.spec.ts"],
      "linter": {
        "rules": {
          "suspicious": {
            "noExplicitAny": "off"
          }
        }
      }
    },
    {
      "include": ["scripts/**/*.ts"],
      "linter": {
        "rules": {
          "suspicious": {
            "noConsoleLog": "off"
          }
        }
      }
    }
  ]
}

Custom Rule Severity

{
  "linter": {
    "rules": {
      "suspicious": {
        "noExplicitAny": "error",      // CI fails
        "noConsoleLog": "warn",        // CI warning
        "noDebugger": "info"           // CI info only
      }
    }
  }
}

Troubleshooting

Biome Not Detecting Files

# Check what Biome sees
bunx biome check --verbose src/

# Ensure files aren't ignored
bunx biome explain --verbose noUnusedVariables

Conflicts with Prettier Formatting

# Migrate Prettier config
bunx biome migrate prettier --write

# Verify compatibility
bunx biome format --write test.js
prettier --write test.js
diff test.js test.js.bak

Editor Not Formatting

VS Code:

• Check extension is installed and enabled
• Verify biome.json exists in workspace root
• Restart TypeScript server: Cmd+Shift+P > "Restart TS Server"

Neovim:

• Check LSP is attached: :LspInfo
• Verify biome binary in PATH: :!which biome
• Check biome.json location matches root_dir

Performance Issues

# Use --max-diagnostics to limit output
bunx biome check --max-diagnostics=50 src/

# Check specific files instead of entire directory
bunx biome check src/problematic-file.ts

# Use --reporter=json for CI
bunx biome check --reporter=json src/