Borrowing it
Nothing to install: this file belongs to michellzappa/headroom. 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/michellzappa/headroom/main/AGENTS.mdgit clone --depth 1 https://github.com/michellzappa/headroomWrote 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/michellzappa/headroom/agents-md)<a href="https://agentmods.dev/instructions/michellzappa/headroom/agents-md"><img src="https://agentmods.dev/badge/instructions/michellzappa/headroom/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/michellzappa/headroom/agents-md"><img src="https://agentmods.dev/badge/instructions/michellzappa/headroom/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 | $0.08031 | $0.08031 |
| Opus 5.5 | $0.03212 | $0.03212 |
| Sonnet 5.5 | $0.01606 | $0.01606 |
| Haiku 4.5 | $0.00803 | $0.00803 |
Grade C, and why
headroom AGENTS.md scanned grade C with 2 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 23d 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.
Downloads and executes remote codehighSupply chain
curl | sh runs whatever the server returns today, which is not necessarily what it returned when this was reviewed.
curl -s localhost:8737/usage | python3 -c 'import json,sys; print([p for p in json.load(sys.stdin)["providers"] if p["id"]=="claude"])' Makes network callslowCapability
Not a fault in itself. Listed so you know the mod talks to something, and to what.
curl -s localhost:8737/usage | python3 -c 'import json,sys; print([p for p in json.load(sys.stdin)["providers"] if p["id"]=="claude"])' How it starts
The opening of the file, as written. The whole thing — 637 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Working on Headroom
Conventions and traps for anyone — human or agent — changing this repo. Several agents often work here at once, which is what most of this is about.
Build
XcodeGen owns the project. Never hand-edit macos/Headroom.xcodeproj; edit
macos/project.yml and regenerate. Always go through the script, which syncs
the embedded host first (bare xcodegen generate fails on a fresh clone):
./scripts/gen-project.sh
Anything touching watchOS — including the iPhone app, which embeds the watch app — needs the beta toolchain on this Mac. The default Xcode reports a watchOS SDK and even has it on disk, but resolves every destination to "watchOS 26.5 is not installed":
export DEVELOPER_DIR=/Applications/Xcode-beta.app/Contents/Developer
Do not pass -sdk iphonesimulator to the iOS build under the beta. It
overrides the SDK for the embedded watch complication too, which then fails
with "'accessoryCorner' is unavailable in iOS" — a red herring.
-destination 'generic/platform=iOS Simulator' alone builds clean.
The green gate, all four targets:
xcodebuild test -project macos/Headroom.xcodeproj -scheme Headroom -configuration Debug -derivedDataPath macos/.build CODE_SIGNING_ALLOWED=NO
xcodebuild build -project macos/Headroom.xcodeproj -scheme HeadroomMobile -destination 'generic/platform=iOS Simulator' -derivedDataPath macos/.build-ios CODE_SIGNING_ALLOWED=NO
xcodebuild build -project macos/Headroom.xcodeproj -scheme HeadroomWatch -destination 'generic/platform=watchOS Simulator' -derivedDataPath macos/.build-watch CODE_SIGNING_ALLOWED=NO
./scripts/check-glossary-copy.sh
A green suite here can be red on CI, and the gap is your own machine's
data. Parts of /usage only exist when the local state behind them does:
history needs ~/.claude session logs, Supabase and Plausible need keys. A
runner has none of it, so a contract assertion that passes against your
served document can fail against a bare one. This has already shipped a red
main once — six history keys looked served on a Mac with 400 days of them
and were absent everywhere else.
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.
- 23d ago Changed · +39 lines · +523 tokens per session fa63b3bca525
- 24d ago Changed · -2 tokens per session 383d0559df16
- 1mo ago First seen · 598 lines · 7,510 tokens per session scan C 987f5ff1eb74
headroom AGENTS.md is an instructions file published in the GitHub repository michellzappa/headroom (264 stars, last pushed 24d ago), licensed MIT. It adds 8,031 tokens to every session, about $0.0321 per session on Opus 5.5. A static security scan graded it C with 2 findings (downloads and executes remote code, makes network calls). No closer match exists in the catalogue, so it is treated as the original; first seen 2026-08-30.
Other instructions, from other repositories
vscode buildNext.instructions.md
Working notes and architecture documentation for the new esbuild-based build system in build/next. Use when making changes to the new build pipeline (transpile/bundle commands, NLS plugin, source-map handling, resource copying, or self-hosting watch tasks).
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.
vscode oss-third-party-notices.instructions.md
Instructions for microsoft/vscode, covering vs code oss third-party-notices pipeline, architecture, pipeline flow in ci, cache eligibility and rollout and applying the notice (cutover).
langchain AGENTS.md
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).
vscode model-prompts.instructions.md
Model-specific prompt authoring and registry guidelines.