biome

A set of instructions for Biome, a tool that checks JavaScript and TypeScript code for issues and formats its layout consistently. It also explains how to configure Biome or move to it from ESLint and Prettier.

In plain words
What is it for?
Setting up Biome, configuring lint rules and formatting, organizing imports, formatting code, and migrating from ESLint or Prettier.
Why use it?
It helps keep code checks and formatting consistent across a project, including when working in continuous integration or editor save hooks. It also prevents new settings from conflicting with an existing project configuration.

Skill for Claude CodeCodex

Install

Getting it into your agent

One page per mod, every tool's command on it. A separate URL per tool would split the same page into five that compete with each other.

agentmods
npx agentmods add skills/usrrname/cursorrules/biome
Any agent
npx skills add usrrname/cursorrules --skill biome
Clone the repo
git clone --depth 1 https://github.com/usrrname/cursorrules

Made for: Claude Code, Codex.

Per session 13 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 566 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. Scan, not verified.
Origin original No closer match found in the catalogue.
Token cost

What it costs to keep this loaded

Counted locally with the o200k_base tokenizer, which is exact for GPT models; Claude uses its own tokenizer and its counts differ. Treat this as one consistent yardstick across the catalogue rather than a bill. Prices are per million input tokens.

ModelPer sessionOnce invoked
Fable 5 $0.00013 $0.00566
Opus 5 $0.00006 $0.00283
Sonnet 5 $0.00003 $0.00113
Haiku 4.5 $0.00001 $0.00057

Measured 2d ago against content hash e3848f00a8cf, method: parsed. Prices are Anthropic first-party input rates as of 2026-08-30, from the pricing page.

Security

Grade A, and why

biome scanned grade A with 0 findings against 26 rules in 11 categories — prompt injection, anti-refusal, data exfiltration, privilege escalation, supply chain, agent snooping, system-prompt leakage, SSRF and excessive agency — measured 2d ago.

A static scan of the body, not an audit. Every finding is printed with the line that produced it so you can judge whether it matters here. A mod is markdown that instructs an agent; that is exactly why what it instructs is worth reading.

Nothing flagged

None of the 26 patterns this scan looks for appear in this file: no shell pipes, no recursive deletes, no credential paths, no hidden text, no instruction-override or anti-refusal phrasing, no agent-config snooping. That is not a guarantee, it is the absence of the things that are checkable.

.claude/skills/biome/SKILL.md · 101 lines

How it starts

The opening of the file, as written. The whole thing — 101 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Biome Skill

Configure and use Biome for fast JavaScript/TypeScript linting and formatting.

When to Use

  • Setting up Biome in a project
  • Migrating from ESLint/Prettier to Biome
  • Configuring lint rules
  • Formatting code with Biome

Critical Rules

Adopt Existing Conventions

If biome.json or biome.jsonc exists in the project:

  • Read and adopt the existing configuration
  • Do not modify existing rules without explicit request
  • Follow the established formatting style (indent, line width, etc.)
  • Respect any disabled rules or custom overrides
  • Use the project's Biome version specified in package.json

Configuration

  • Use biome.json or biome.jsonc for configuration
  • Extend recommended rules as base
  • Configure formatter and linter together
  • Set up import organization

Performance

  • Biome is 10-100x faster than ESLint/Prettier
  • Use for CI/CD pipelines
  • Format on save in editor
  • Run checks in pre-commit hooks

Migration

  • Start with biome migrate from ESLint/Prettier configs
  • Disable conflicting rules gradually
  • Maintain parity during transition
  • Remove old configs after migration complete

Best Practices

  • Enable all recommended rules by default
  • Use biome check for lint + format in CI
  • Configure import sorting
  • Set up editor integration

Examples

biome.json

{
  "$schema": "https://biomejs.dev/schemas/1.5.3/schema.json",
  "organizeImports": {
    "enabled": true
  },
  "linter": {
    "enabled": true,
    "rules": {
      "recommended": true,
      "correctness": {
        "noUnusedVariables": "error"
      }
    }
  },
  "formatter": {
    "enabled": true,
    "indentStyle": "space",
    "indentWidth": 2,
    "lineWidth": 80
  }
}

Commands

# Check lint and format
biome check .

# Check with auto-fix
biome check --apply .

# Format only
biome format --write .

# Lint only
biome lint --apply .
  • /typescript - TypeScript best practices
  • /react - React patterns that Biome enforces

Read the full file on GitHub · 101 lines

Changes

What this file has done since we first saw it

Hashed on every crawl. A supply-chain change to an agent config is a question of when, not whether, so the history is kept rather than the latest state alone.

  1. 2d ago First seen · 101 lines · 13 tokens per session scan A e3848f00a8cf

Subscribe to this mod's changes

biome is a skill published in the GitHub repository usrrname/cursorrules (10 stars, last pushed 4mo ago), licensed ISC. It adds 13 tokens to every session and 566 once invoked, about $0.0001 per session on Opus 5. A static security scan graded it A with 0 findings. No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-31.