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 majiayu000/spellbook --skill build-product-demogit clone --depth 1 https://github.com/majiayu000/spellbookWrote 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/majiayu000/spellbook/build-product-demo)<a href="https://agentmods.dev/skills/majiayu000/spellbook/build-product-demo"><img src="https://agentmods.dev/badge/skills/majiayu000/spellbook/build-product-demo/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/majiayu000/spellbook/build-product-demo"><img src="https://agentmods.dev/badge/skills/majiayu000/spellbook/build-product-demo.svg" alt="Reviewed on agentmods" width="80" 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 | $0.00117 | $0.02745 |
| Opus 5 | $0.00059 | $0.01373 |
| Sonnet 5 | $0.00023 | $0.00549 |
| Haiku 4.5 | $0.00012 | $0.00275 |
Grade A, and why
build-product-demo 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.
How it starts
The opening of the file, as written. The whole thing — 274 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Build Product Demo
Turn verified product behavior into a compact proof story. Treat the final media as an executable claim about the product, not as a decorated feature list.
Choose the mode
- Plan: inspect the product and produce the brief, evidence inventory, feature coverage, director treatment, script, and beat plan.
- Produce: complete the plan, create deterministic setup and capture tooling, record, edit, and verify the final media.
- Diagnose: inspect an existing demo, identify the first broken layer, and revise the smallest responsible artifact. Check truth, story, visible state change, attention, narration/action alignment, capture, then encoding.
If the user asks to “make” or “finish” the demo, default to Produce. Do not stop at a script while safe, in-scope production work remains.
Establish the boundary
-
Resolve the exact product repository, revision, runtime, audience, channel, target duration, aspect ratio, language, available assets, and publishing scope. Inspect before guessing.
-
Read repository instructions and existing demos, screenshots, tests, fixtures, launch scripts, and marketing claims. Search before adding a new recorder or seed path.
-
Separate immutable product facts, creative choices, and missing production facts. Do not turn an unknown into a visual claim.
-
Select one reference benchmark: the user's strongest previous demo, a product-native launch video, or a clearly named quality bar. Record what to preserve and what to avoid. Do not rely on generic taste words.
-
Choose one audience doubt and one proof proposition. Complete:
The audience doubts whether [product claim]. The demo proves [outcome] by showing [observable change]. -
Define the opening and landing state. Reject a concept whose product or audience state is materially unchanged at the end.
Read directing.md before selecting features or writing beats. Read production.md before recording, generating narration, or using deterministic fixtures.
What ships with it
8 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 · 274 lines · 117 tokens per session scan A 054e9f9e0039
build-product-demo is a skill published in the GitHub repository majiayu000/spellbook (278 stars, last pushed yesterday), licensed MIT. It adds 117 tokens to every session and 2,745 once invoked, about $0.0006 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 2026-09-03.
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