biome

---
name: biome
description: Use when you want one fast Rust-based tool to format and lint JavaScript, TypeScript, JSX, JSON, and CSS, replacing Prettier and ESLint.
source: https://biomejs.dev
generated: 2026-07-02T18:41:27.818Z
category: other
audience: engineers
---

## When to use

- Formatting and linting a JS/TS project from a single tool and config file
- Replacing a separate Prettier plus ESLint setup to cut config and install size
- Running format-and-lint checks in CI with a single biome ci command
- Adding auto-fix on save or as a pre-commit step for consistent style

## Key concepts

### Unified formatter and linter

Biome combines formatting (Prettier-like) and linting (ESLint-like) in one toolchain, written in Rust for speed. It aims for high Prettier formatting compatibility out of the box.

### biome.json

The single configuration file at the project root. It has sections like formatter, linter, javascript, json, and files to control rules, indentation, line width, and ignored paths.

### Rule groups and recommended set

Lint rules are organized into groups such as correctness, suspicious, style, and complexity. A recommended set is enabled by default; rules can be toggled to error/warn/off in biome.json.

### Safe vs unsafe fixes

biome check --write applies safe automatic fixes; --write --unsafe also applies fixes that may change behavior or intent and should be reviewed.

### Single binary, no plugins

Biome ships as one binary with batteries included, so most projects need no plugin ecosystem. This reduces dependency footprint compared to ESLint's plugin model.

## API reference

```
biome check [path]
```

Run formatter, linter, and import sorting checks together and report issues without modifying files.

```
npx @biomejs/biome check ./src
npx @biomejs/biome check --write ./src
```

```
biome format --write [path]
```

Format files in place; omit --write to print or only report formatting differences.

```
npx @biomejs/biome format --write ./src
npx @biomejs/biome format ./src
```

```
biome lint [path]
```

Run only the linter and report rule violations; add --write to apply safe fixes.

```
npx @biomejs/biome lint ./src
npx @biomejs/biome lint --write ./src
```

```
biome ci [path]
```

Run formatting and linting in a non-writing CI mode that fails on any issue.

```
npx @biomejs/biome ci ./src
```

```
biome init
```

Generate a starter biome.json config file in the current directory.

```
npx @biomejs/biome init
# creates biome.json:
# {
#   "formatter": { "enabled": true, "indentStyle": "tab" },
#   "linter": { "enabled": true, "rules": { "recommended": true } }
# }
```

## Gotchas

- biome check is read-only by default; you must pass --write to actually apply changes
- --write --unsafe can change code behavior; review the diff before committing unsafe fixes
- Prettier compatibility is very high but not exact; expect a few formatting differences when migrating
- Language support is focused on JS/TS/JSX, JSON(C), and CSS — coverage for other languages is still expanding
- If results seem to ignore files, check the files.includes/ignore settings and .gitignore handling in biome.json
- Editor extensions need the Biome binary or version matching biome.json; mismatched versions can format differently

---
Generated by SkillMake from https://biomejs.dev on 2026-07-02T18:41:27.818Z.
Verify against source before relying on details.

File: ~/.claude/skills/biome/SKILL.md