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 45ck/skill-harness --skill host-instruction-drift-checkergit clone --depth 1 https://github.com/45ck/skill-harnessWrote 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/45ck/skill-harness/host-instruction-drift-checker)<a href="https://agentmods.dev/skills/45ck/skill-harness/host-instruction-drift-checker"><img src="https://agentmods.dev/badge/skills/45ck/skill-harness/host-instruction-drift-checker/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/45ck/skill-harness/host-instruction-drift-checker"><img src="https://agentmods.dev/badge/skills/45ck/skill-harness/host-instruction-drift-checker.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 | $0.00045 | $0.00364 |
| Opus 5 | $0.00023 | $0.00182 |
| Sonnet 5 | $0.00009 | $0.00073 |
| Haiku 4.5 | $0.00005 | $0.00036 |
Grade A, and why
host-instruction-drift-checker 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 10d 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
Host Instruction Drift Checker
Use this skill when a repo supports multiple coding-agent hosts or when a baseline update may change agent behavior.
Process
- Identify the canonical instruction source for the repo.
- Inventory host surfaces:
AGENTS.mdCLAUDE.mdAGENT_INSTRUCTIONS.md.claude/agents/*.codex/agents/*.agents/skills/*/SKILL.md.claude/skills/*/SKILL.md.codex/skills/*/SKILL.md.cursor/rules/*.mdc.github/copilot-instructions.md
- Compare only the behavioral contract: scope, permissions, stop rules, evidence, generated-file ownership, and profile/installer semantics.
- Treat host-specific syntax as normal, not drift.
- Classify each mismatch as generated drift, overlay drift, stale doctrine, policy conflict, missing host surface, or intentional host specialization.
- Prefer updating canonical source and regenerating derived surfaces over hand-editing generated agent files.
Output
Canonical Source
Surfaces Checked
Drift Findings
Intentional Differences
Regeneration Path
Required Manual Review
Avoid
- forcing every host file to contain identical prose
- editing generated files as if they were canonical
- ignoring Cursor
.mdcand Copilot surfaces when the repo advertises those hosts - treating missing evidence gates as minor wording drift
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.
- 10d ago First seen · 44 lines · 45 tokens per session scan A 2a8d1cb8123a
host-instruction-drift-checker is a skill published in the GitHub repository 45ck/skill-harness (15 stars, last pushed 2mo ago), licensed MIT. It adds 45 tokens to every session and 364 once invoked, about $0.0002 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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do-it-architecture
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do-it-review
Use to assess requirements and implementation quality independently, or to resolve a batch of review findings.
do-it-code-quality
Use when designing, changing, or debugging code to locate causal ownership and close the affected behavior.
do-it-core
Use when repository work needs a shared baseline for intent, facts, causal changes, and honest evidence.
do-it-decide
Use when uncertainty about a choice, plan, dependency, or handoff could materially change what gets built.
do-it-skill-authoring
Use when creating or revising a do-it skill so its trigger and unique professional judgment are useful without prescribing ceremony.