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 tacoda/keystone --skill keystone-check-driftgit clone --depth 1 https://github.com/tacoda/keystoneWrote 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/tacoda/keystone/keystone-check-drift)<a href="https://agentmods.dev/skills/tacoda/keystone/keystone-check-drift"><img src="https://agentmods.dev/badge/skills/tacoda/keystone/keystone-check-drift/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/tacoda/keystone/keystone-check-drift"><img src="https://agentmods.dev/badge/skills/tacoda/keystone/keystone-check-drift.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 | $0.00026 | $0.00291 |
| Opus 5 | $0.00013 | $0.00146 |
| Sonnet 5 | $0.00005 | $0.00058 |
| Haiku 4.5 | $0.00003 | $0.00029 |
Grade A, and why
keystone-check-drift 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.
What it actually says
keystone:check-drift — fast pre-verify drift check
Compares the in-progress diff against loaded charter rules. Fires before the full computational sensor suite — catches the obvious case where the agent is implementing something the rules explicitly disallow.
Canonical playbook: .charter/actions/check-drift.md. Sensor
contract at .charter/sensors/drift.md. Full discipline at
.charter/guides/process/implementation.md.
Run
Open .charter/actions/check-drift.md and execute every
activity.
When to trigger
- Mid-implementation, before running
/keystone:verify. - After a large refactor that touched many regions — make sure the loaded idiom rules still apply.
- When
/keystone:verifykeeps failing on the same rule — drift is often the upstream cause.
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 · 43 lines · 26 tokens per session scan A 8ce28b5e26a1
keystone-check-drift is a skill published in the GitHub repository tacoda/keystone (44 stars, last pushed 2mo ago), licensed MIT. It adds 26 tokens to every session and 291 once invoked, about $0.0001 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 2026-08-30.
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