Claude Code for Biome — Workflow Guide

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The Setup

You are replacing ESLint and Prettier with Biome, the fast all-in-one linter and formatter written in Rust. Claude Code can configure Biome rules, fix linting errors, and format code, but it keeps generating ESLint and Prettier configurations alongside Biome or uses ESLint rule names that do not exist in Biome.

What Claude Code Gets Wrong By Default

  1. Creates .eslintrc and .prettierrc files. Claude generates ESLint and Prettier configs when you ask for linting setup. With Biome, everything goes in a single biome.json file — no other config files needed.

  2. Uses ESLint rule names in Biome config. Claude writes "no-unused-vars": "error" in biome.json. Biome uses its own rule naming: "noUnusedVariables" under "linter": { "rules": { "correctness": { ... } } }.

  3. Runs npx eslint --fix for auto-fixes. Claude defaults to ESLint CLI commands. Biome uses npx @biomejs/biome check --fix for combined linting and formatting, or biome format --write for formatting only.

  4. Installs multiple dev dependencies. Claude adds eslint, prettier, eslint-config-*, and dozens of plugins. Biome is a single dependency: @biomejs/biome. No plugins, no config inheritance chains.

The CLAUDE.md Configuration

# Biome Linter/Formatter Project

## Tooling
- Linter + Formatter: Biome (@biomejs/biome)
- Config: biome.json at project root
- NO ESLint, NO Prettier — Biome replaces both

## Biome Rules
- Format: npx @biomejs/biome format --write .
- Lint: npx @biomejs/biome lint .
- Both: npx @biomejs/biome check --fix .
- Config uses camelCase rule names, not ESLint kebab-case
- Rules organized by category: correctness, suspicious, style, complexity
- Use "recommended": true for sensible defaults
- Override per-file with biome.json "overrides" array

## Conventions
- Run biome check before commits (pre-commit hook)
- Indent: tabs (Biome default, do not change to spaces)
- Line width: 100 characters
- Quote style: double quotes
- Semicolons: always
- Never add ESLint or Prettier — Biome handles everything
- Ignore generated files in biome.json "files.ignore"

Workflow Example

You want to migrate from ESLint + Prettier to Biome. Prompt Claude Code:

“Migrate this project from ESLint and Prettier to Biome. Remove the old config files and dependencies, create a biome.json with equivalent rules, and update the package.json scripts.”

Claude Code should delete .eslintrc.*, .prettierrc, remove ESLint/Prettier packages from package.json, install @biomejs/biome, create biome.json with "recommended": true, and update scripts to use biome check --fix instead of eslint --fix && prettier --write.

Common Pitfalls

  1. Import sorting conflicts. Claude configures Biome’s import sorting but keeps the eslint-plugin-import sort order. Biome sorts imports differently by default. Remove any other import sorting tools and let Biome handle it exclusively.

  2. VS Code extension conflicts. Claude does not update VS Code settings. If you have the ESLint and Prettier extensions active alongside the Biome extension, you get duplicate formatting and conflicting fixes. Disable the ESLint and Prettier extensions for the workspace.

  3. Biome does not support all ESLint rules. Claude migrates every ESLint rule one-to-one. Some ESLint ecosystem rules (like React-specific or TypeScript-ESLint rules) may not have Biome equivalents yet. Check Biome’s rule list before assuming a migration is complete.