Prototype

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

If the user passed arguments, treat them as the question the prototype should answer.

Pick a branch

Identify which question is being answered — from the user's prompt, the arguments, the surrounding code, or by asking if the user is around. The litmus test: if the user could answer the question by looking at a screen, it's UI. If they'd need to push buttons and watch state change, it's logic.

• "Does this logic / state model feel right?" → LOGIC.md. Build a tiny interactive 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.

Scaffolder

Before writing boilerplate, run the bundled scaffolder to generate the repetitive parts (switcher component, TUI shell, variant stubs). Then fill in the interesting parts — the actual variants or the domain logic.

# UI prototype: generates PrototypeSwitcher + variant shells
npx tsx ${CLAUDE_PLUGIN_ROOT}/skills/prototype/scripts/scaffold.ts ui --variants 3 --framework next --outdir ./src/app/settings

# Logic prototype: generates portable logic module + TUI shell
npx tsx ${CLAUDE_PLUGIN_ROOT}/skills/prototype/scripts/scaffold.ts tui --name checkout-flow --outdir ./src/checkout

The scaffolder handles React UI (Next, React Router, Vite) and TypeScript TUI. For other UI frameworks, it creates the directory structure with React components — adapt them to your framework.

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. Use a naming convention that makes it impossible to confuse with production code — prefix files or folders with __prototype- or put them in a prototype/ subfolder next to the target module. 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 error handling beyond what makes the prototype runnable, no abstractions. Don't build a test suite — if a single assertion would save you from a dumb mistake while iterating, that's fine, but if you're writing more than one you've left prototype territory. The point is to learn something fast and then delete it.
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. Delete or absorb when done. When the prototype has answered its question, either delete it or fold the validated decision into the real code — don't leave it rotting in the repo.

When done

The answer is the only thing worth keeping from a prototype. Capture it somewhere durable (commit message, ADR, issue, or a NOTES.md next to the prototype) along with the question it was answering. If the user is around, that capture is a quick conversation; if not, leave the placeholder so they (or you, on the next pass) can fill in the verdict before deleting the prototype.