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.
npx skills add The-Artificer-of-Ciphers-LLC/skills-from-the-artificer --skill postels-lawgit clone --depth 1 https://github.com/The-Artificer-of-Ciphers-LLC/skills-from-the-artificerWrote 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/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/postels-law)<a href="https://agentmods.dev/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/postels-law"><img src="https://agentmods.dev/badge/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/postels-law/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/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/postels-law"><img src="https://agentmods.dev/badge/skills/the-artificer-of-ciphers-llc/skills-from-the-artificer/postels-law.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 | $0.00109 | $0.00852 |
| Opus 5 | $0.00055 | $0.00426 |
| Sonnet 5 | $0.00022 | $0.00170 |
| Haiku 4.5 | $0.00011 | $0.00085 |
Grade A, and why
postels-law 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 12d 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 — 64 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Postel's Law (Robustness Principle)
"Be conservative in what you send, liberal in what you accept." — Jon Postel, RFC 760, 1980
The core idea
When building systems that communicate with other systems, Postel recommended:
- Send only well-formed, minimal, correct data. Don't rely on the other side tolerating your quirks.
- Accept data that is slightly off. Be forgiving of minor variations, extra fields, or slightly non-standard inputs from senders.
This principle shaped the early internet. HTML parsers that accepted malformed tags, TCP stacks that handled variations in packet formatting — the early web grew partly because implementors were lenient about what they accepted.
The case for it
Real-world senders make mistakes. Other systems, other developers, other versions of software — they will send you data that is slightly wrong. If you reject anything imperfect, you become brittle and hard to integrate with.
Interoperability requires tolerance. When you have many producers of data and many consumers, allowing slightly varied input enables the ecosystem to grow. Strict rejection creates integration friction.
Graceful degradation. A system that accepts imperfect input can provide partial value; one that rejects it provides none.
The modern critique — and important caveats
Postel's Law has critics, and their arguments are strong enough to warrant caution:
Permissive acceptance hides bugs. When you silently accept malformed input and make sense of it, the sender never finds out they're sending bad data. You've obscured an error that should have been fixed at the source. Over time this creates "compatibility debt" — everyone depends on your interpretation of malformed data.
Security vulnerabilities. Many security exploits rely on parsers accepting inputs that are technically invalid. Permissive HTML parsing has been a rich source of XSS vulnerabilities. Permissive SQL parsing has enabled injection attacks. Being liberal in what you accept often means being liberal in what you execute.
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.
- 12d ago First seen · 64 lines · 109 tokens per session scan A 17fbd0e6a2e4
postels-law is a skill published in the GitHub repository The-Artificer-of-Ciphers-LLC/skills-from-the-artificer (4 stars, last pushed 10d ago), licensed MIT. It adds 109 tokens to every session and 852 once invoked, about $0.0005 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.
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