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 agentmods add skills/richfrem/agent-plugins-skills/prototype-buildernpx skills add richfrem/agent-plugins-skills --skill prototype-buildergit clone --depth 1 https://github.com/richfrem/agent-plugins-skillsWrote 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/richfrem/agent-plugins-skills/prototype-builder)<a href="https://agentmods.dev/skills/richfrem/agent-plugins-skills/prototype-builder"><img src="https://agentmods.dev/badge/skills/richfrem/agent-plugins-skills/prototype-builder.svg" alt="Measured on agentmods" 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 | $0.00076 | $0.01147 |
| Opus 5 | $0.00038 | $0.00574 |
| Sonnet 5 | $0.00015 | $0.00229 |
| Haiku 4.5 | $0.00008 | $0.00115 |
Grade A, and why
prototype-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 yesterday.
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 — 118 lines — stays where its author put it; the contents beside it link to each section on GitHub.
Role
This skill coordinates the full prototype build cycle. It does NOT build components directly. Building is handled by subagent-driven-prototyping. Layout confirmation is handled by visual-companion. This skill connects those two steps and guides the SME through the full journey from plan to working prototype.
HARD-GATE Check
This is the first thing that runs, before any other step.
Check: does exploration/discovery-plans/ exist and contain at least one .md file?
If NO plan exists:
"Before we can build, I need to understand what we're building first. Can we start with a planning session? It only takes a few minutes and it'll make sure what we build is exactly what you need."
Stop. Do not continue. Do not suggest workarounds. Do not attempt to build without a plan.
If a plan file exists: Read the most recent .md file in exploration/discovery-plans/. Check that it contains either:
- A
## SME Approvalsection, or - A
PLAN_STATUS: APPROVEDline
If neither is present:
"A Discovery Plan exists but hasn't been approved yet. Please review the plan and confirm approval before we begin building."
What ships with it
4 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.
- yesterday First seen · 118 lines · 76 tokens per session scan A 783984366026
prototype-builder is a skill published in the GitHub repository richfrem/agent-plugins-skills (6 stars, last pushed yesterday), licensed MIT. It adds 76 tokens to every session and 1,147 once invoked, about $0.0004 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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