code-quality-lint

name	code-quality-lint
description	This skill should be used when the user asks to "set up eslint", "configure prettier", "add biome", "set up ruff", "configure lint-staged", "add formatter", "configure linter", or needs reference for linter/formatter/lint-staged configuration in their project.
version	1.1.0

Linter, Formatter, and lint-staged Reference

Configuration reference for code quality tools across ecosystems. Use this skill when you need to set up, modify, or troubleshoot specific linting and formatting tools.

Ecosystem Guide

Ecosystem	Recommended Tool	Reference
JavaScript/TypeScript	Biome (new) or ESLint + Prettier	Below
Python	Ruff	references/python-linting.md
Rust	Clippy + rustfmt	references/rust-linting.md
Go	golangci-lint + gofmt	references/go-linting.md

---

JavaScript / TypeScript

Biome (Recommended for New Projects)

Biome is a single tool that replaces ESLint + Prettier -- faster, zero-config defaults, consistent formatting.

# Install
npm add -D @biomejs/biome

# Initialize
npx biome init

biome.json:

{
  "$schema": "https://biomejs.dev/schemas/2.0.0/schema.json",
  "organizeImports": {
    "enabled": true
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true
    }
  },
  "formatter": {
    "enabled": true,
    "indentStyle": "space",
    "indentWidth": 2
  }
}

lint-staged config:

{
  "*.{js,jsx,ts,tsx,json,jsonc,css}": ["biome check --write --no-errors-on-unmatched"]
}

When to choose Biome over ESLint + Prettier:

• New projects without existing ESLint config
• Want simpler toolchain (one tool, one config)
• Performance-sensitive CI (Biome is significantly faster)

ESLint 9 (Flat Config)

ESLint 9 uses flat config (eslint.config.js) instead of the legacy .eslintrc.* format.

npm add -D eslint @eslint/js typescript-eslint

eslint.config.js:

import js from '@eslint/js';
import tseslint from 'typescript-eslint';

export default tseslint.config(
  js.configs.recommended,
  ...tseslint.configs.recommended,
  {
    ignores: ['dist/', 'node_modules/', '.next/']
  }
);

lint-staged config:

{
  "*.{js,jsx,ts,tsx}": ["eslint --fix"]
}

Prettier

npm add -D prettier

.prettierrc:

{
  "semi": true,
  "singleQuote": true,
  "trailingComma": "es5",
  "tabWidth": 2,
  "printWidth": 100
}

lint-staged config (with ESLint):

{
  "*.{js,jsx,ts,tsx}": ["eslint --fix", "prettier --write"],
  "*.{json,md,yml,yaml,css}": ["prettier --write"]
}

---

lint-staged Configuration

lint-staged runs linters/formatters only on staged files, making pre-commit hooks fast regardless of project size.

Installation

npm add -D lint-staged

Configuration Examples

Minimal (Biome):

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

ESLint + Prettier:

{
  "*.{js,jsx,ts,tsx}": ["eslint --fix", "prettier --write"],
  "*.{json,md,yml,yaml,css,html}": ["prettier --write"]
}

TypeScript-aware (with type checking on staged files):

{
  "*.{ts,tsx}": ["eslint --fix", "prettier --write"],
  "*.{js,jsx}": ["eslint --fix", "prettier --write"]
}

Note: Running tsc in lint-staged is usually not recommended because TypeScript type checking requires the full project context, not just staged files. Put tsc --noEmit in your pre-push hook instead.

For advanced patterns, monorepo config, and non-JS ecosystems: see references/lint-staged-advanced.md

---

Reference Files

File	Contents	Read when...
references/python-linting.md	Ruff config, Black/Flake8 legacy	Setting up Python linting or formatting
references/rust-linting.md	Clippy + rustfmt config	Setting up Rust linting or formatting
references/go-linting.md	golangci-lint + gofmt config	Setting up Go linting or formatting
references/lint-staged-advanced.md	Config locations, custom functions, monorepo patterns, non-JS ecosystems, ESLint+Prettier conflicts, troubleshooting	Advanced lint-staged setup, debugging, or polyglot projects