A prototype isdisposable code that answers a question. The question determines the shape.
A prototype is throwaway code that answers a question. The question decides the shape.
Pick a branch
Identify what question is being answered—from the user's prompt, the surrounding code, or by asking if the user is present:
Identify which question is being answered — from the user's prompt, the surrounding code, or by asking if the user is around:
- "Does this logic/state model feel right?" → LOGIC.md. Build a small interactive terminal app that pushes the state machine through the cases that are hard to reason about on paper.
"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 multiple markedly different UI variants on a single route, switched via a URL search parameter and a floating bottom bar.
"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 is unreachable, pick the branch that better matches the surrounding code (backend module → logic; page or component → UI), and state the assumption at the top of the prototype.
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.
Rules that apply to both
- Disposable from day one, and clearly marked. Put the prototype code near where it will actually be used (right next to the module or page it prototypes), so the context is obvious—but name it so a casual reader can tell this is a prototype and not production. For disposable UI routes, follow the project's existing routing conventions; do not invent a new top-level structure.
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.
- One command to run. Whatever the project's existing task runner supports—
pnpm <name>、python <path>、bun <path>, etc. The user should be able to start it without thinking.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. - No persistence by default. State lives in memory. Persistence is the thing the prototypeis examining, not something it should depend on. If the question explicitly involves a database, use a temporary database or a local file with a clear "prototype—delete me" name.
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.
- Skip polish. Write no tests, and write no error handling or abstractions beyond what makes the prototyperunnable. The point is to learn something quickly and then delete it.
Skip the polish. No tests, no error handling beyond what makes the prototype runnable, no abstractions. The point is to learn something fast and then delete it.
- Expose state. After every operation (logic) or every variant switch (UI), print or render the complete relevant state so the user can see what changed.
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.
- Delete or absorb when done. Once the prototype has answered its question, either delete it or fold the validated decision into the real code—don't let it rot in the repository.
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 answeris the only thing in the prototype worth keeping. Capture it somewhere durable (a commit message, ADR, issue, or a NOTES.mdnext to the prototype), along with the question it was answering. If the user is present, capturing it is a quick conversation; if not, leave a placeholder so they (or you on the next pass) can fill in the conclusion before deleting the prototype.
The answer is the only thing worth keeping from a prototype. Capture it somewhere durable (commit message, ADR, issue, or a
NOTES.mdnext 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.