Borrowing it
Nothing to install: this file belongs to BigCactusLabs/dead-letter. 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/BigCactusLabs/dead-letter/main/AGENTS.mdgit clone --depth 1 https://github.com/BigCactusLabs/dead-letterWrote 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/bigcactuslabs/dead-letter/agents-md)<a href="https://agentmods.dev/instructions/bigcactuslabs/dead-letter/agents-md"><img src="https://agentmods.dev/badge/instructions/bigcactuslabs/dead-letter/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/bigcactuslabs/dead-letter/agents-md"><img src="https://agentmods.dev/badge/instructions/bigcactuslabs/dead-letter/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 | $0.02125 | $0.02125 |
| Opus 5.5 | $0.00850 | $0.00850 |
| Sonnet 5.5 | $0.00425 | $0.00425 |
| Haiku 4.5 | $0.00213 | $0.00213 |
Grade A, and why
dead-letter 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 4d 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.
The source is not reproduced here
A licence we could not identify
The repository carries a LICENSE file, but it is custom or dual enough that GitHub cannot name it and neither can this catalogue. Unknown terms are not permission, so the body is not copied here. Read the licence at the source and decide for yourself.
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.
- 4d ago Changed · +4 tokens per session 35efb06885bf
- 6d ago Changed · +13 tokens per session 4ff0cdea3200
- 18d ago Changed · +1 lines · +15 tokens per session 56a306881ff5
- 19d ago Changed · +7 lines · +108 tokens per session 0dc882f8341a
- 28d ago Changed · +6 tokens per session e460291172d1
- 1mo ago Changed · +2 lines · +29 tokens per session d0211aa48a29
- 1mo ago Changed · +6 lines · +157 tokens per session f7fcd6d99495
- 1mo ago Changed · +31 lines · +355 tokens per session 813761d9c5ed
- 1mo ago Changed · +25 lines · +390 tokens per session fdc33f56c3a4
- 1mo ago First seen · 93 lines · 1,048 tokens per session scan A 6de6837a7ec2
dead-letter AGENTS.md is an instructions file published in the GitHub repository BigCactusLabs/dead-letter (8 stars, last pushed yesterday), with no licence file. It adds 2,125 tokens to every session, about $0.0085 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 2026-08-31.
Other instructions, from other repositories
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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.
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Copilot instructions for microsoft/vscode, covering vs code copilot instructions, project overview, root folders, core architecture (src/ folder) and built-in extensions (extensions/ folder).
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Copilot instructions for denoland/deno, covering deno development guide for github copilot, network access, high level overview, key directories and key files to understand first.