prototype

prototype is a skill for Claude Code, Codex from FradSer/dotclaude. It costs 39 tokens per session (684 once invoked), scanned A, a copy of prototype, MIT.

A throwaway coding workflow for answering one design question before building the real feature. It creates either a small terminal program to explore logic or several switchable UI variations.

In plain words
What is it for?
Use it to explore difficult state transitions or compare possible layouts for a page or component.
Why use it?
It lets you test whether a state model or interface makes sense without committing the main codebase to an unproven design.

Skill for Claude CodeCodex

Written for Claude Code and Codex: shipped in a Claude Code plugin, but also agents/openai.yaml present. Also seen: names the AskUserQuestion tool.

Part of the mattpocock plugin — 46 skills shipped together

Good fit Use it to explore difficult state transitions or compare possible layouts for a page or component.

Compare 6 skills from other repositories ↓
Install with agentmods
npx agentmods add skills/fradser/dotclaude/prototype
Install

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.

Any agent
npx skills add FradSer/dotclaude --skill prototype
Clone the repo
git clone --depth 1 https://github.com/FradSer/dotclaude

Made for: Claude Code, Codex.

Or install mattpocock, the plugin that ships this one along with the rest of its 46 skills.

Wrote 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.

agentmods badge for prototype

README.md
[![agentmods](https://agentmods.dev/badge/skills/fradser/dotclaude/prototype/github.svg)](https://agentmods.dev/skills/fradser/dotclaude/prototype)
Your own site
<a href="https://agentmods.dev/skills/fradser/dotclaude/prototype"><img src="https://agentmods.dev/badge/skills/fradser/dotclaude/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.

agentmods 80×15 button for prototype

Your own site · 80×15
<a href="https://agentmods.dev/skills/fradser/dotclaude/prototype"><img src="https://agentmods.dev/badge/skills/fradser/dotclaude/prototype.svg" alt="Reviewed on agentmods" width="80" height="20"></a>
Per session 39 Skills are progressive disclosure: only the name and description are preloaded; the body loads when the skill is used.
When invoked 684 The whole file, excluding the scripts and references it only reads on demand.
Security scan A 0 findings. A grade says what 26 rules found in the file — not that it is safe.
Origin 73% copy Near-identical to another mod in the catalogue.
Token cost

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.

ModelPer sessionOnce invoked
Fable 5.1 $0.00039 $0.00684
Opus 5.5 $0.00016 $0.00274
Sonnet 5.5 $0.00008 $0.00137
Haiku 4.5 $0.00004 $0.00068

Measured 23d ago against content hash 515bdcc72d8b, method: parsed. Prices are Anthropic first-party input rates as of 2026-10-07, from the pricing page.

Security

Grade A, and why

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 23d 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.

Origin

This is a copy

73% identical to prototype — 18 lines differ, which has more behind it and is treated as the original. This page carries a canonical link to it rather than competing with it.

mattpocock/skills/engineering/prototype/SKILL.md · 31 lines

How it starts

The opening of the file, as written. The whole thing — 31 lines — stays where its author put it; the contents beside it link to each section on GitHub.

Prototype

A prototype is throwaway code that answers a question. The question decides the shape.

Pick a branch

Identify which question is being answered: from the user's prompt, the surrounding code, or by using the AskUserQuestion tool to ask the user if they're around:

  • "Does this logic / state model feel right?" → LOGIC.md. Build a tiny interactive terminal app that pushes the state machine through cases that are hard to reason about on paper.
  • "What should this look like?" → UI.md. Generate several radically different UI variations on a single route, switchable via a URL search param and a floating bottom bar.

The two branches produce very different artifacts: getting this wrong wastes the whole prototype. If the question is genuinely ambiguous and the user isn't reachable, default to whichever branch better matches the surrounding code (a backend module → logic; a page or component → UI) and state the assumption at the top of the prototype.

CRITICAL: The question decides the shape

Identify the question being answered before building: "does this logic / state model feel right?" takes LOGIC.md, "what should this look like?" takes UI.md; getting this wrong wastes the whole prototype. Throwaway from day one: no tests, no polish, no persistence: keep the answer, delete the code.

Rules that apply to both

  1. Throwaway from day one, and clearly marked as such. Locate the prototype code close to where it will actually be used (next to the module or page it's prototyping for) so context is obvious: but name it so a casual reader can see it's a prototype, not production. For throwaway UI routes, obey whatever routing convention the project already uses; don't invent a new top-level structure.
  2. One command to run. Whatever the project's existing task runner supports: pnpm <name>, python <path>, bun <path>, etc. The user must be able to start it without thinking.
  3. No persistence by default. State lives in memory. Persistence is the thing the prototype is checking, not something it should depend on. If the question explicitly involves a database, hit a scratch DB or a local file with a clear "PROTOTYPE: wipe me" name.
  4. Skip the polish. No tests, no error handling beyond what makes the prototype runnable, no abstractions. The point is to learn something fast.
  5. Surface the state. After every action (logic) or on every variant switch (UI), print or render the full relevant state so the user can see what changed.
  6. Capture it when done. Fold any validated decision into the real code, then capture the prototype itself as a primary source: commit it to a throwaway branch, out of main, and leave a context pointer to that branch on the implementation issue. Capture the answer too: the verdict and the question it settled: in the issue or a commit. The main branch keeps only the validated decision.

Read the full file on GitHub · 31 lines

Files

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.

Changes

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.

  1. 23d ago First seen · 31 lines · 39 tokens per session scan A 515bdcc72d8b

Subscribe to this mod's changes

prototype is a skill published in the GitHub repository FradSer/dotclaude (594 stars, last pushed 8d ago), licensed MIT. It adds 39 tokens to every session and 684 once invoked, about $0.0002 per session on Opus 5.5. A static security scan graded it A with 0 findings. It is 73% identical to prototype, differing in 18 lines, and is treated as a copy.

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