Biome Configuration & Usage

Biome is a fast formatter and linter that replaces Prettier and ESLint. This skill provides guidelines for configuring Biome, managing ignores, and fixing common issues.

1. Configuration (biome.json)

The core configuration lives in biome.json at the project root.

Standard Structure

{
  "$schema": "https://biomejs.dev/schemas/1.9.4/schema.json",
  "vcs": {
    "enabled": true,
    "clientKind": "git",
    "useIgnoreFile": true
  },
  "files": {
    "ignoreUnknown": false,
    "ignore": [] 
  },
  "formatter": {
    "enabled": true,
    "indentStyle": "tab"
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true
    }
  }
}

Note: The files.ignore property in biome.json is sometimes flagged as invalid depending on the schema version. The robust way to ignore files is using .biomeignore.

2. Ignoring Files

.biomeignore (Recommended)

Place a .biomeignore file in the project root. It works exactly like .gitignore.

# .biomeignore
node_modules
.next
dist
build
scripts/

ignore vs includes

• •files.includes: Whitelist specific files to process.
• •.biomeignore: Blacklist files to exclude.

3. Common CLI Commands

• •

  Check (Lint + Format Verification):

  bash

  biome check .    # Check all files
  biome check src/ # Check specific folder
  

• •

  Apply Fixes (Safe):

  bash

  biome check --write .
  

• •

  Apply All Fixes (Unsafe): Use this for organizing imports or suppression sorting, but review changes carefully.

  bash

  biome check --write --unsafe .
  

• •

  Format Only:

  bash

  biome format --write .
  

4. VS Code Integration

Ensure the Biome extension is installed and set as the default formatter for supported languages.

// .vscode/settings.json
{
  "[javascript]": {
    "editor.defaultFormatter": "biomejs.biome"
  },
  "[typescript]": {
    "editor.defaultFormatter": "biomejs.biome"
  },
  "[typescriptreact]": {
    "editor.defaultFormatter": "biomejs.biome"
  },
  "[json]": {
    "editor.defaultFormatter": "biomejs.biome"
  }
}

5. Troubleshooting

• •

  Property ignore is not allowed: If you see this error in biome.json, remove the files.ignore array and use .biomeignore instead.

• •

  "Imports are unused" errors: Biome is strict about unused imports. If an import is only used for types, use import type.

  ts

  import type { User } from "./types";