Biome is a web-development toolchain that formats and checks source code for languages such as JavaScript, TypeScript, JSX, and CSS. Developers use its command-line and language-server interfaces to maintain code quality in web projects. Catalogue add-ons extend workflows around the toolchain.
Borrowing it
Nothing to install: this file belongs to biomejs/biome. Take a copy, put it at the same path in your own repository, and replace the rules that are about this project with yours.
curl -O https://raw.githubusercontent.com/biomejs/biome/main/AGENTS.mdgit clone --depth 1 https://github.com/biomejs/biomeWrote this? Show the measurements
A badge with what this costs and how it scanned, read live from this page, so it follows the numbers instead of freezing them. Markdown for a README, HTML for a documentation site or a project page.
[](https://agentmods.dev/instructions/biomejs/biome/agents-md)<a href="https://agentmods.dev/instructions/biomejs/biome/agents-md"><img src="https://agentmods.dev/badge/instructions/biomejs/biome/agents-md/github.svg" alt="Measured on agentmods" height="20"></a>Or the 80×15 button, for a site that already has a row of RSS and ATOM ones. Only the verdict fits; the numbers stay here.
<a href="https://agentmods.dev/instructions/biomejs/biome/agents-md"><img src="https://agentmods.dev/badge/instructions/biomejs/biome/agents-md.svg" alt="Reviewed on agentmods" width="80" height="20"></a>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.
| Model | Per session | Once invoked |
|---|---|---|
| Fable 5.1 | $0.01127 | $0.01127 |
| Opus 5.5 | $0.00451 | $0.00451 |
| Sonnet 5.5 | $0.00225 | $0.00225 |
| Haiku 4.5 | $0.00113 | $0.00113 |
Grade A, and why
biome AGENTS.md 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 16d 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.
How it starts
The opening of the file, as written. The whole thing — 89 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Agent Guidelines for Contributing to Biome
This file contains rules that apply to every automated contribution. Detailed workflows live in .agents/skills/ or the contributing guides they reference.
[!NOTE] Automated agents may add 🤖🤖🤖 to the end of a PR title to opt into the streamlined merge process.
Communication
- Keep responses short, factual, and technical.
- Do not use emojis in source, comments, rustdoc, diagnostics, tests, snapshots, commits, issues, PR communication, or agent output. The PR-title marker above is the only exception.
- Do not claim a Biome function, module, behavior, or convention exists without an exact file and line, a source excerpt, or a reproducible command.
- If evidence is unavailable, state that rather than presenting the claim as fact.
Before Editing
- Read files in full before wide-ranging changes, before editing an unfamiliar file, and whenever the user requests an investigation or audit.
- Inspect the surrounding implementation and current contributing guide instead of copying remembered APIs or commands.
- Preserve unrelated worktree changes. Never revert or rewrite changes you did not make.
Implementation Gate
- Make the smallest change that satisfies the requested behavior.
- Add tests for code changes. Bug fixes require a case that fails without the fix.
- Run the narrowest relevant tests first, then broader checks when justified.
- Run the tests of the current crate to check possible regressions.
- Review generated snapshots as behavior, not disposable output.
- Run
just fandjust lbefore committing.
Load testing-codegen for test fixtures, snapshots, and generator selection.
Required generated artifacts:
If you change an .ungram file, run:
just gen-grammar <lang>just gen-formatter --allow-dirty
If you change the name of a lint rule or assist action, run:
just gen-rulesjust gen-configuration
Bindings and other full analyzer outputs may be left to the CI Autofix job unless they are needed for local verification.
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.
- 16d ago Changed · +6 lines · +152 tokens per session 825456f67007
- 24d ago Changed · -7 tokens per session 4e7000f18cf5
- 1mo ago Changed · +3 lines · +5 tokens per session 5fe47043edf3
- 1mo ago Changed · -7 tokens per session 131b867f923c
- 1mo ago Changed · +7 tokens per session d82fedc09a8f
- 1mo ago First seen · 80 lines · 977 tokens per session scan A 0d0159497979
biome AGENTS.md is an instructions file published in the GitHub repository biomejs/biome (26,016 stars, last pushed today), licensed Apache-2.0. It adds 1,127 tokens to every session, about $0.0045 per session on Opus 5.5. 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 2026-08-30.
Other instructions, from other repositories
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next.js AGENTS.md
AGENTS.md instructions for vercel/next.js, covering next.js development guide, codebase structure, monorepo overview, core package: packages/next and other important packages.
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AGENTS.md instructions for langchain-ai/langchain, covering global development guidelines for the langchain monorepo, corridor security analysis, project architecture and context, monorepo structure and development tools & commands.
vscode copilot-instructions.md
Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
deepseek-harness AGENTS.md
AGENTS.md instructions for deepseek-ai/deepseek-harness, covering agents.md, pre-stable apis and released session data, repository layout, commands and host sandbox failures.