Biome Tooling

This skill covers using Biome, a fast all-in-one toolchain for formatting and linting JavaScript/TypeScript code.

What is Biome?

Biome is a performant toolchain that provides:

• Formatting (replaces Prettier)
• Linting (replaces ESLint)
• Fast (written in Rust, 25x faster than Prettier)
• Zero config (sensible defaults)
• Single tool (no conflicts between tools)

Installation

npm install --save-dev @biomejs/biome

Configuration

Create biome.json in your project root:

{
  "$schema": "https://biomejs.dev/schemas/1.5.3/schema.json",
  "organizeImports": {
    "enabled": true
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true
    }
  },
  "formatter": {
    "enabled": true,
    "formatWithErrors": false,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 100,
    "lineEnding": "lf"
  },
  "javascript": {
    "formatter": {
      "quoteStyle": "double",
      "trailingComma": "es5",
      "semicolons": "always",
      "arrowParentheses": "always",
      "bracketSpacing": true,
      "jsxQuoteStyle": "double"
    }
  }
}

Package.json Scripts

{
  "scripts": {
    "format": "biome format --write .",
    "format:check": "biome format .",
    "lint": "biome lint .",
    "lint:fix": "biome lint --apply .",
    "check": "biome check --apply .",
    "ci": "biome ci ."
  }
}

Script explanations:

• format - Format all files in place
• format:check - Check if files are formatted (CI)
• lint - Show linting errors
• lint:fix - Fix auto-fixable issues
• check - Format + lint + organize imports (recommended)
• ci - Check everything without modifying files (for CI)

Basic Usage

Format Files

# Format all files
npm run format

# Format specific files
npx biome format --write src/

# Check formatting without modifying
npx biome format src/

Lint Files

# Lint all files
npm run lint

# Lint and fix
npm run lint:fix

# Lint specific files
npx biome lint src/

All-in-One Check

# Format, lint, and organize imports
npm run check

# Check without modifying (for CI)
npm run ci

File Configuration

Include/Exclude Files

{
  "files": {
    "include": ["src/**/*.ts", "src/**/*.tsx"],
    "ignore": [
      "node_modules",
      "dist",
      "build",
      ".sst",
      "*.config.js"
    ]
  }
}

Override for Specific Files

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

Linter Rules

Enable Recommended Rules

{
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true
    }
  }
}

Customize Rule Groups

{
  "linter": {
    "rules": {
      "recommended": true,
      "complexity": {
        "noExcessiveCognitiveComplexity": "warn",
        "noForEach": "off"
      },
      "style": {
        "noNegationElse": "error",
        "useTemplate": "warn"
      },
      "suspicious": {
        "noExplicitAny": "warn",
        "noArrayIndexKey": "warn"
      }
    }
  }
}

Rule Categories

Complexity:

• noExcessiveCognitiveComplexity
• noForEach
• useFlatMap
• useSimplifiedLogicExpression

Correctness:

• noUnreachable
• noUndeclaredVariables
• noUnusedVariables
• useExhaustiveDependencies

Performance:

• noAccumulatingSpread
• noDelete

Security:

• noDangerouslySetInnerHtml
• noDangerouslySetInnerHtmlWithChildren

Style:

• noArguments
• noImplicitBoolean
• noNegationElse
• useBlockStatements
• useTemplate

Suspicious:

• noArrayIndexKey
• noCommentText
• noExplicitAny
• noShadowRestrictedNames

Formatter Configuration

Basic Options

{
  "formatter": {
    "enabled": true,
    "formatWithErrors": false,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 100,
    "lineEnding": "lf"
  }
}

JavaScript-Specific Options

{
  "javascript": {
    "formatter": {
      "quoteStyle": "double",
      "jsxQuoteStyle": "double",
      "quoteProperties": "asNeeded",
      "trailingComma": "all",
      "semicolons": "always",
      "arrowParentheses": "always",
      "bracketSpacing": true,
      "bracketSameLine": false
    }
  }
}

Import Organization

{
  "organizeImports": {
    "enabled": true
  }
}

Biome will:

• Remove unused imports
• Sort imports
• Group imports (built-in, external, internal)

VSCode Integration

Install Extension

Install "Biome" extension from VSCode marketplace.

VSCode Settings

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

Git Hooks

Using Husky + lint-staged

npm install --save-dev husky lint-staged

{
  "lint-staged": {
    "*.{js,jsx,ts,tsx}": [
      "biome check --apply --no-errors-on-unmatched"
    ]
  }
}

# Setup husky
npx husky init
echo "npx lint-staged" > .husky/pre-commit

CI/CD Integration

GitHub Actions

name: CI

on: [push, pull_request]

jobs:
  check:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v3
      - uses: actions/setup-node@v3
        with:
          node-version: 20
      - run: npm ci
      - run: npm run ci
        # Runs: biome ci .

GitLab CI

check:
  stage: test
  script:
    - npm ci
    - npm run ci

Migration from ESLint + Prettier

Remove Old Tools

npm uninstall eslint prettier @typescript-eslint/parser @typescript-eslint/eslint-plugin

# Remove config files
rm .eslintrc.js .prettierrc .prettierignore .eslintignore

Install Biome

npm install --save-dev @biomejs/biome

Initialize Config

npx @biomejs/biome init

Update Scripts

Replace:

{
  "scripts": {
    "lint": "eslint .",
    "format": "prettier --write ."
  }
}

With:

{
  "scripts": {
    "check": "biome check --apply .",
    "ci": "biome ci ."
  }
}

Common Patterns

Ignore Generated Files

{
  "files": {
    "ignore": [
      "*.generated.ts",
      "build/",
      ".sst/",
      "coverage/"
    ]
  }
}

Strict Mode for Production

{
  "linter": {
    "rules": {
      "recommended": true,
      "suspicious": {
        "noExplicitAny": "error",
        "noArrayIndexKey": "error"
      }
    }
  }
}

Relaxed Rules for Tests

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

Best Practices

1. Use in Pre-commit Hooks

# Ensures all committed code is formatted and linted
npx lint-staged

2. Run in CI/CD

- run: npm run ci

Fail the build if code doesn't pass checks.

3. Format on Save

Configure your editor to format on save.

4. Keep Config Minimal

Start with defaults, only configure what you need:

{
  "$schema": "https://biomejs.dev/schemas/1.5.3/schema.json",
  "formatter": {
    "lineWidth": 100
  },
  "linter": {
    "rules": {
      "recommended": true
    }
  }
}

5. Use with TypeScript

Biome works great with TypeScript:

{
  "javascript": {
    "parser": {
      "unsafeParameterDecoratorsEnabled": true
    }
  }
}

Performance Benefits

Biome is significantly faster than ESLint + Prettier:

# Formatting 5000 files
Prettier: ~30 seconds
Biome:    ~1 second

# Linting 5000 files
ESLint: ~45 seconds
Biome:  ~2 seconds

Troubleshooting

"Command not found: biome"

# Install locally
npm install --save-dev @biomejs/biome

# Or use npx
npx @biomejs/biome check .

"Parse errors" on valid code

Check your biome.json parser options:

{
  "javascript": {
    "parser": {
      "unsafeParameterDecoratorsEnabled": true
    }
  }
}

VSCode not formatting

1. Install Biome extension
2. Check it's the default formatter
3. Reload VSCode

Conflicts with existing tools

Remove ESLint and Prettier:

npm uninstall eslint prettier

Advanced Configuration

Per-Project Settings

{
  "extends": ["@company/biome-config"],
  "formatter": {
    "lineWidth": 120
  }
}

Custom Rule Severity

{
  "linter": {
    "rules": {
      "suspicious": {
        "noExplicitAny": {
          "level": "warn",
          "fix": "none"
        }
      }
    }
  }
}

Comparison: Biome vs ESLint + Prettier

Feature	Biome	ESLint + Prettier
Speed	25x faster	Slower
Setup	Single tool	Two tools + config
Conflicts	None	Possible
Rules	Growing	Extensive
Plugins	Limited	Many
Memory	Lower	Higher

When to Use Biome

✅ Use Biome when:

• Starting a new project
• Speed is important
• You want simpler tooling
• You're okay with opinionated defaults

⚠️ Consider alternatives when:

• You need specific ESLint plugins
• You have complex custom rules
• Team is heavily invested in ESLint

Migration Checklist

• Install Biome
• Create biome.json
• Update package.json scripts
• Remove ESLint/Prettier
• Update pre-commit hooks
• Update CI/CD pipelines
• Configure VSCode
• Test on existing code
• Update team documentation

Further Reading

• Biome Docs: https://biomejs.dev/
• Biome GitHub: https://github.com/biomejs/biome
• Biome Playground: https://biomejs.dev/playground/
• VSCode Extension: https://marketplace.visualstudio.com/items?itemName=biomejs.biome