Build a throwaway build-a-throwaway-prototype to answer a design question. Use when the user wants to sanity-check whether a state model or logic feels right, or explore what a UI should look like.
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---
name: build-a-throwaway-prototype
description: Build a throwaway build-a-throwaway-prototype to answer a design question. Use when the user wants to sanity-check whether a state model or logic feels right, or explore what a UI should look like.
---
# Prototype
A build-a-throwaway-prototype is **throwaway code that answers a question**. The question decides the shape.
## Pick a branch
Identify which question is being answered, using the user's prompt, the surrounding code, or by asking if the user is around:
- **"Does this logic / state model feel right?"** → [LOGIC.md](LOGIC.md). Build a single shareable HTML file (free-play buttons plus tabbed guided walkthroughs) that pushes the state machine through cases that are hard to reason about on paper, and that a non-developer can drive.
- **"What should this look like?"** → [UI.md](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, so getting this wrong wastes the whole build-a-throwaway-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 build-a-throwaway-prototype.
## Rules that apply to both
1. **Throwaway from day one, and clearly marked as such.** Locate the build-a-throwaway-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 build-a-throwaway-prototype, not production. For throwaway UI routes, obey whatever routing convention the project already uses; don't invent a new top-level structure.
2. **Trivial to run.** A UI build-a-throwaway-prototype starts from one command in the project's task runner: `pnpm <name>`, `python <path>`, `bun <path>`, etc. A logic demo is a single HTML file the user double-clicks. Either way, no thinking required to start it.
3. **No persistence by default.** State lives in memory. Persistence is the thing the build-a-throwaway-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 build-a-throwaway-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 build-a-throwaway-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.
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*Adapted from [`mattpocock/skills`](https://github.com/mattpocock/skills), MIT licence, Copyright (c) 2026 Matt Pocock. Renamed and cross-linked for this collection; the method is his. Full licence text in [`LICENSES/mattpocock-skills-MIT.txt`](../../LICENSES/mattpocock-skills-MIT.txt).*
