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 davistroy/claude-marketplace --skill spec-to-prototypegit clone --depth 1 https://github.com/davistroy/claude-marketplaceWrote 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/davistroy/claude-marketplace/spec-to-prototype)<a href="https://agentmods.dev/skills/davistroy/claude-marketplace/spec-to-prototype"><img src="https://agentmods.dev/badge/skills/davistroy/claude-marketplace/spec-to-prototype/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/davistroy/claude-marketplace/spec-to-prototype"><img src="https://agentmods.dev/badge/skills/davistroy/claude-marketplace/spec-to-prototype.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 | $0.00106 | $0.01951 |
| Opus 5 | $0.00053 | $0.00975 |
| Sonnet 5 | $0.00021 | $0.00390 |
| Haiku 4.5 | $0.00011 | $0.00195 |
Grade A, and why
spec-to-prototype 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 — 167 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Spec-to-Prototype Builder
Build self-contained HTML/CSS visual prototypes from specification documents. Produces shareable single-file demos with realistic data and navigation — no backend, no build tools, no framework dependencies.
When to Use
- User has a spec, reference doc, design system doc, or component description
- Goal is a visual demo, not a functional application
- Stakeholder presentations, design validation, or vision casting
- User says "prototype", "mockup", "dummy UI", "visual demo"
Not for: Production apps, functional forms, real data integration, or creative/original UI design (use frontend-design skill directly for those).
Process
digraph prototype_flow {
rankdir=TB;
node [shape=box, style=rounded];
read [label="1. Read & analyze spec"];
identify [label="2. Identify prototypable views"];
ask [label="3. Ask clarifying questions\n(batched, one AskUserQuestion call)"];
design [label="4. Invoke frontend-design skill"];
build [label="5. Build single HTML file"];
test [label="6. Test in browser"];
fix [label="7. Fix issues found"];
done [label="Deliver"];
read -> identify -> ask -> design -> build -> test;
test -> fix [label="issues"];
fix -> test;
test -> done [label="clean"];
}
Step 1 — Read the Spec
Read the full spec document. Extract:
- Components/elements described (with names, anatomy, behaviors)
- Layout structure (shells, sidebars, content areas, navigation)
- Visual language (colors, typography, spacing, icons mentioned)
- Data model (what entities exist, what fields they have)
- Interaction patterns (what opens what, navigation flows)
Step 2 — Identify Prototypable Views
Determine what can be shown as static views. Propose 2-3 options to the user:
- Which views/scenarios best showcase the spec?
- Which combination hits the most components?
- What's the minimum set of views for maximum stakeholder impact?
Step 3 — Ask Clarifying Questions
Ask the four essential questions in one AskUserQuestion call — this is a short
scoping exchange before a build, not an interview, and batching costs the user one
interaction instead of four:
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 · 167 lines · 106 tokens per session scan A 4c7945fb36e2
spec-to-prototype is a skill published in the GitHub repository davistroy/claude-marketplace (5 stars, last pushed 5d ago), licensed MIT. It adds 106 tokens to every session and 1,951 once invoked, about $0.0005 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 2026-09-04.
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