AI Engineering from Scratch is a free, open-source curriculum that teaches people to build AI systems through lessons and reusable artifacts such as prompts, skills, agents, and MCP servers. It is for learners who want practical foundations or want to create AI applications, and the catalogue skills support parts of that curriculum.
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 rohitg00/ai-engineering-from-scratch --skill skill-invocation-routergit clone --depth 1 https://github.com/rohitg00/ai-engineering-from-scratchWrote 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/rohitg00/ai-engineering-from-scratch/skill-invocation-router)<a href="https://agentmods.dev/skills/rohitg00/ai-engineering-from-scratch/skill-invocation-router"><img src="https://agentmods.dev/badge/skills/rohitg00/ai-engineering-from-scratch/skill-invocation-router.svg" alt="Measured on agentmods" height="20"></a>- NVIDIA SkillSpector pass
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 | $0.00036 | $0.00332 |
| Opus 5 | $0.00018 | $0.00166 |
| Sonnet 5 | $0.00007 | $0.00066 |
| Haiku 4.5 | $0.00004 | $0.00033 |
Grade A, and why
skill-invocation-router 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 8d 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
Skill invocation router
Use this skill when a host needs an auditable activation policy rather than one undifferentiated invocable flag.
- Read
references/invocation-model.mdand classify the requested channel. - Review
assets/host-policy.jsonas an example adapter configuration, not a portable standard. - Run
python3 scripts/simulate_invocation.py --policy assets/host-policy.json --actor ACTOR --name NAME --description DESCRIPTION --query QUERY [--explicit-name NAME] [--caller-name NAME] [--depth N] [--user-invocable true|false] [--disable-model-invocation true|false]. - For a human, application, skill, or harness request, require an exact discovered name and its channel-specific allowlist.
- For a skill caller, also require caller identity, a non-cyclic target, and a bounded composition depth.
- For a model or autonomous agent request, remove candidates that the actor or recognized host extensions make ineligible.
- Score only the remaining descriptions. Select the strongest eligible match or abstain when no eligible candidate clears the threshold.
- Return the JSON decision with the adapter, channel, score, and policy reason.
Activation loads instructions. It does not approve tools, filesystem changes, network access, secret use, or bundled scripts.
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.
- 8d ago First seen · 23 lines · 36 tokens per session scan A 7376d66c0da8
skill-invocation-router is a skill published in the GitHub repository rohitg00/ai-engineering-from-scratch (52,653 stars, last pushed yesterday), licensed MIT. It adds 36 tokens to every session and 332 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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skill-invocation-router
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