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 HetCreep/CoalMine --skill drift-canarygit clone --depth 1 https://github.com/HetCreep/CoalMineWrote 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/hetcreep/coalmine/drift-canary)<a href="https://agentmods.dev/skills/hetcreep/coalmine/drift-canary"><img src="https://agentmods.dev/badge/skills/hetcreep/coalmine/drift-canary/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/hetcreep/coalmine/drift-canary"><img src="https://agentmods.dev/badge/skills/hetcreep/coalmine/drift-canary.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 | $0.00078 | $0.01979 |
| Opus 5 | $0.00039 | $0.00989 |
| Sonnet 5 | $0.00016 | $0.00396 |
| Haiku 4.5 | $0.00008 | $0.00198 |
Grade A, and why
drift-canary 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 6d 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 — 83 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Drift Canary (Contract & Schema Drift Audit)
Language: Generate EVERYTHING at runtime in the user's language — questions, answer options, menu labels, recommendations, report narrative. Detect from their messages; never default to English just because this file is English. English is allowed only for technical terms: commands, paths, code identifiers, severity labels (CRITICAL/HIGH/MEDIUM/LOW), and tier names (Light/Standard/Heavy).
Config reads — every config key, always the CASCADE, never the bare project file: ~/.claude/.coalmine.json first, then the project config (own agent dir → other known agent dirs → legacy <gitroot>/.coalmine.json), project wins per key. A bare project read is ABSENT on a machine configured only globally, so it silently yields defaults.
Audit code to ensure changes do not break backward compatibility or cause database/API mismatches.
Auditing Categories
- Breaking Schema Migrations — dropping columns, changing types, or adding non-null columns without defaults (crashes on deploy).
- API Contract breaking changes — modifying existing REST/GraphQL properties, removing endpoints, or adding required query fields that break old clients.
- Serialization mismatches — editing properties in serialized payloads (JSON, Protobuf, XML) without deserialization fallbacks.
- Library Contract Drift — changing a public method signature in a shared library without a deprecated wrapper.
- Environment Configuration drift — introducing new required config keys (
.env/ OS vars) without defaults or fallback.
Expand/contract migration rules, per-format serialization fallbacks, and the breaking-vs-additive API checklist: read references/checks.md before scanning.
Scope: honor .coalmine.json schemaPaths / migrationDirs if set — scan those globs/dirs; else infer by inspecting the repo.
Discipline
- Style Drift Resolution (Fix mode): when an approved fix touches mixed-style code, conform the minority patterns to the dominant style (highest average usage) to minimize churn — never start a standalone style refactor.
What ships with it
3 files 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.
- 6d ago Changed · +2 lines d64da19b5542
- 10d ago First seen · 81 lines · 78 tokens per session scan A ae902ff33741
drift-canary is a skill published in the GitHub repository HetCreep/CoalMine (12 stars, last pushed today), licensed Apache-2.0. It adds 78 tokens to every session and 1,979 once invoked, about $0.0004 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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