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 impactbrussels/AINativeOS --skill write-the-claude-mdgit clone --depth 1 https://github.com/impactbrussels/AINativeOSWrote 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/impactbrussels/ainativeos/write-the-claude-md)<a href="https://agentmods.dev/skills/impactbrussels/ainativeos/write-the-claude-md"><img src="https://agentmods.dev/badge/skills/impactbrussels/ainativeos/write-the-claude-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/skills/impactbrussels/ainativeos/write-the-claude-md"><img src="https://agentmods.dev/badge/skills/impactbrussels/ainativeos/write-the-claude-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 | $0.00168 | $0.01428 |
| Opus 5 | $0.00084 | $0.00714 |
| Sonnet 5 | $0.00034 | $0.00286 |
| Haiku 4.5 | $0.00017 | $0.00143 |
Grade A, and why
write-the-claude-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 9d 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 — 104 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Write the CLAUDE.md
A clever prompt dies the instant the context window clears. The agent forgets, reconstructs a theory of your system from whatever it can see, and builds against that improvised theory, slightly differently every session, until one repository houses three half-systems that almost agree. The master file is the cure. It is the memory the model does not have: the one document read at the top of every session so the work starts where you left it, not from a guess. Write it before the first feature, not after the first regression.
The method
Author one master file, mirror it to every platform, and keep it alive with a session-end ritual.
Full anatomy, worked before-and-after, and anti-patterns: references/master-file-anatomy.md.
Step 1: Write the seven sections, and nothing else
The file earns its keep by being short and current. Include the standing context an agent would otherwise guess; exclude anything that lives better in code or goes stale by Friday.
| Section | What it holds | Keep out |
|---|---|---|
| What this is | One paragraph: the product and its one closed loop. | Marketing copy. |
| System inventory | The four pillars named: Brain, Memory, Planning, Tools. | API keys, secrets. |
| Principles | The non-negotiable rules of this codebase. | Generic best practice the model already knows. |
| Constraints | The limits a newcomer would break by accident. | Anything enforced by a linter or test. |
| Decisions | Dated trade-offs made and why, newest first. | Decisions already reversed; prune them. |
| Glossary pointers | Links to the domain terms, not the definitions. | Full definitions that drift from source. |
| Update ritual | The one-line rule for keeping this file alive. | A changelog of every commit. |
Step 2: Mirror it across every platform you use
The same source serves four runtimes. A rule in only one file is a rule the other three agents break.
| Platform | File it reads |
|---|---|
| Claude Code | CLAUDE.md |
| Codex | AGENTS.md |
| Cursor | .cursor/rules/<name>.mdc |
| Gemini CLI | GEMINI.md |
What ships with it
1 file beside SKILL.md in the same directory: the scripts, references and assets a skill reads on demand. Not counted in the per-session cost; read them before you install if any of them is executable.
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.
- 9d ago First seen · 104 lines · 168 tokens per session scan A ea55d6cdda94
write-the-claude-md is a skill published in the GitHub repository impactbrussels/AINativeOS (1 stars, last pushed 2mo ago), licensed Apache-2.0. It adds 168 tokens to every session and 1,428 once invoked, about $0.0008 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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