Biome

Biome is a fast, all-in-one toolchain for JavaScript and TypeScript projects. Written in Rust, it combines formatting and linting into a single binary with zero dependencies.

Benefits

• Lightning fast — Formats large codebases in milliseconds
• All-in-one toolchain — No more juggling ESLint, Prettier, and other tools
• Zero dependencies — One binary does everything with consistent behavior
• Multi-language support — Handles JavaScript, TypeScript, JSX, TSX, JSON, CSS, GraphQL, and HTML
• Smart sorting — Automatically organizes imports, JSX attributes, and Tailwind CSS classes

Usage

{
  "extends": ["ultracite/biome/core"]
}

Add framework presets as needed:

{
  "extends": [
    "ultracite/biome/core",
    "ultracite/biome/react",
    "ultracite/biome/next"
  ]
}

Configuration Approach

Ultracite's Biome configuration uses an opt-in approach. This means every rule is explicitly specified in the configuration — nothing is implicitly inherited. This gives you full visibility into exactly which rules are enabled and at what level.

Rule Categories

Biome organizes rules into the following categories:

Accessibility (a11y)

Rules that enforce ARIA attributes, semantic HTML, keyboard navigation, and other accessibility best practices. Examples include requiring alt text for images, valid ARIA roles, and proper heading structure.

Complexity

Rules that reduce cognitive complexity and enforce best practices. Examples include preferring for...of over forEach, using optional chaining, and avoiding excessive nesting.

Correctness

Rules that prevent common errors and enforce type safety. Examples include catching unused variables, invalid regex patterns, unreachable code, and incorrect use of hooks.

Performance

Rules that optimize code for better runtime performance. Examples include avoiding accumulating spread in loops, discouraging barrel files, and enforcing efficient patterns.

Security

Rules that prevent security vulnerabilities. Examples include blocking eval(), requiring rel="noopener" on external links, and flagging dangerous innerHTML usage.

Style

Rules that enforce consistent code style. Examples include preferring const over let, using template literals, enforcing consistent type definitions, and file naming conventions.

Suspicious

Rules that catch suspicious patterns that might indicate bugs. Examples include flagging debugger statements, duplicate object keys, and implicit type coercion.

Formatter Settings

Ultracite configures Biome's formatter with these defaults:

• Indentation: 2 spaces
• Line Width: 80 characters
• Line Ending: LF (Unix-style)
• Semicolons: Always required
• Trailing Commas: ES5 style
• Arrow Parentheses: Always include

Rule Reference

For the complete list of rules and their settings, see the Biome configuration on GitHub.

VS Code Extension

Install the Biome extension for VS Code:

code --install-extension biomejs.biome