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 external-skill-fixture-buildergit 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/external-skill-fixture-builder)<a href="https://agentmods.dev/skills/45ck/skill-harness/external-skill-fixture-builder"><img src="https://agentmods.dev/badge/skills/45ck/skill-harness/external-skill-fixture-builder/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/external-skill-fixture-builder"><img src="https://agentmods.dev/badge/skills/45ck/skill-harness/external-skill-fixture-builder.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 | $0.00034 | $0.00319 |
| Opus 5.5 | $0.00014 | $0.00128 |
| Sonnet 5.5 | $0.00007 | $0.00064 |
| Haiku 4.5 | $0.00003 | $0.00032 |
Grade A, and why
external-skill-fixture-builder 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 1mo 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
External Skill Fixture Builder
Use this skill when a third-party ecosystem pattern should be tested by skill-harness but should not become a live dependency.
Process
- Choose the fixture lane by install posture, not by brand:
- pure
SKILL.mdpack - plugin manifest
- Cursor
.mdcrules - Codex/Claude/Cursor subagents
- MCP/tool config
- generated record/replay skill
- Beads or task-memory repo
- multi-agent workspace layout
- pure
- Use minimal synthetic fixtures when possible.
- Use pinned external snapshots only when real structure matters and license/provenance allows it.
- Keep fixtures out of global user directories and live install caches.
- Make the fixture assert one behavior: parse, classify, trust recommendation, drift detection, render target, or installer opt-in.
- Add a command or check that proves the fixture is exercised.
Output
Fixture Lane
Source Or Synthetic Basis
Files Included
Expected Classification
Risk Flags Expected
Check Command
Follow-Up Adoption Question
Avoid
- making fixtures large mirrors of public repos
- using fixtures as a back door for third-party adoption
- mixing fixture coverage with default installer behavior
- storing credentials, real traces, browser recordings, or private task state in fixtures
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.
- 1mo ago First seen · 43 lines · 34 tokens per session scan A 84b5413bcd22
external-skill-fixture-builder is a skill published in the GitHub repository 45ck/skill-harness (15 stars, last pushed 4mo ago), licensed MIT. It adds 34 tokens to every session and 319 once invoked, about $0.0001 per session on Opus 5.5. 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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instructions
Use at the start of any task, before taking action, to load the always-on workflow rules covering skill invocation, communication, skill scripts, and the conventions of the environment the session is running in.