prototype

name	prototype
description	Rapid prototyping workflow that deliberately skips standards to validate a risky concept fast. Produces throwaway code and a structured prototype report. Use to retire the riskiest assumption from /brainstorm before committing to architecture, or to validate a novel mechanic before adding to the sprint.
argument-hint	<assumption-to-test>
user-invocable	true
allowed-tools	Read, Glob, Grep, Write, Edit, Bash, AskUserQuestion
model	sonnet

Prototype

A prototype is a question the codebase poses to reality. It is explicitly not production code: no tests, no review, no PRD, no ADR, no manifest pinning. The output is a one-page report that tells the team whether the assumption holds — and whatever was learned along the way.

Outputs:

• prototypes/<name>/ — the prototype's code (intentionally walled off from src/)
• prototypes/<name>/REPORT.md — what was built, what was learned, what to do with the learning

---

Purpose / When to Run

Run when:

• The concept doc's "Riskiest Assumption" needs validation before architecture commitment
• A novel mechanic or framework feature needs to be tried before adding to a PRD
• A perf concern needs a quick measurement before locking budgets
• A library / SDK needs vetting before an ADR commits to it

Do not run for:

• Features that already have PRDs and ADRs (use /dev-story in the second skill set)
• Bug investigations (use the bug-fix workflow in the second skill set)
• Refactors of existing code (those are real stories)

Inputs

• Assumption to test (required, free text)
• Optional: design/concept.md Section 8 (Riskiest Assumption) for context

Outputs

• prototypes/<name>/ — code
• prototypes/<name>/REPORT.md

---

Phase 1: Frame the Question

If no argument was passed, ask:

• Prompt: "What assumption are you testing?"
• Free text — capture as kebab-case for the prototype name.

The framing matters. Use AskUserQuestion:

• Prompt: "Re-frame the assumption as a yes/no question. Pick or write:"
• Options: derived from the input — e.g., for "people will tap during a session":
  • Q: Can users complete the core action in <3 seconds while doing something else?
  • Q: Does the gesture work mid-activity without misfires?
  • Custom (free text)

The question becomes the prototype's success criterion.

---

Phase 2: Define Success / Fail Criteria

Use AskUserQuestion:

• "What evidence would prove yes?" — free text
• "What evidence would prove no?" — free text

Pin both. The prototype is done when one or the other is observed — not when "the code runs."

Example:

• YES: "User completes the action in <3s in 80% of test runs across 5 testers."
• NO: "Median completion >5s, or misfire rate >20%."

---

Phase 3: Constrain the Prototype

The point is to retire the question, not to build a feature. Constrain explicitly:

• Time budget: ask the user (1-3 days typical). Anything over 3 days is no longer a prototype — it is a feature in disguise.
• Code quality bar: "throwaway" — explicit non-goals: tests, accessibility, error handling, dark mode, localization, performance optimization.
• Scope: the smallest demo that shows yes/no.
• Hardware target: which device(s) this needs to run on. Often a single primary device.

---

Phase 4: Pick an Approach

If the prototype lives in this repo's framework, use the existing framework setup. If the prototype needs a different stack (e.g., a quick HTML/JS sketch to validate a UX gesture before reimplementing in RN), allow it — call out the cross-stack mismatch in the report.

For mobile-specific prototypes, common patterns:

• Static UX prototype — Figma click-through with no code (the skill can produce a Figma-style spec instead of code)
• Throwaway native — quick SwiftUI / Compose / RN screen wired only to demonstrate the interaction
• Library spike — install the SDK, run the canonical demo, measure
• Performance spike — write the smallest possible reproduction; measure cold start / TTI / frame rate
• Backend stub — mock the API; validate the front-end behavior under known responses

Pick one with the user and document the choice.

---

Phase 5: Build

Set up prototypes/<name>/. Inside it:

• README.md (one paragraph: question + how to run)
• A subdirectory or files for the actual prototype code
• A .gitignore at this level if needed

Build the smallest demo that answers the question. Skip:

• Tests (this code dies)
• Accessibility (intentional non-goal)
• Error handling (happy path only)
• Localization
• Dark mode
• Performance tuning beyond what is measured

Write inline comments noting why each shortcut is acceptable for a prototype.

---

Phase 6: Run the Test

Run the prototype on the target device(s). Capture observations:

• Did the success criterion hold?
• What was measured (time, accuracy, perceived feel)?
• What surprised the testers?
• What edge cases surfaced that the PRD will need to address?
• What technical realities surfaced (a library limitation, an OS quirk)?

If user testing is involved, run with at least 3 testers. Capture each tester's session quickly — verbatim quote, time-to-action, any misfires.

---

Phase 7: Write the Report

prototypes/<name>/REPORT.md:

# Prototype Report: <name>

> **Question**: <the framed question from Phase 1>
> **Run on**: <date>
> **Time spent**: <hours / days>
> **Verdict**: <YES / NO / INCONCLUSIVE>

## Setup
- Stack: <RN / Flutter / native / web / Figma>
- Device(s): <list>
- Testers: <count, optional names>

## Method
<one paragraph — what was built, how it was tested>

## Success / Fail criteria (pre-defined)
- YES if: <criterion>
- NO if: <criterion>

## Findings
- <observation 1, with measurement if applicable>
- <observation 2>
- <observation 3>

### Quotes (if user-tested)
> "<verbatim>" — Tester A
> "<verbatim>" — Tester B

### Measurements
| Metric | Result | Target |
|--------|--------|--------|
| Time to action | 2.4s median | <3s |
| Misfire rate | 12% | <20% |

## Verdict
<YES / NO / INCONCLUSIVE>: <one paragraph explaining why the data leads to this verdict>

## What this means

For YES:
- Proceed with: <PRD section, ADR, sprint commitment>
- Update concept.md Section 8 to mark the assumption retired
- Capture lessons in the relevant PRD's "Implementation Hooks" section

For NO:
- Do not pursue this approach. Alternatives that emerged: <list>
- Update concept.md Section 8 with the new riskiest assumption
- Re-run `/brainstorm` if the core JTBD is at risk

For INCONCLUSIVE:
- More data needed. Specifically: <what would resolve it>
- Run a second prototype focused on <narrower question>

## Lessons (mobile-specific)
- iOS: <anything platform-specific>
- Android: <anything>
- Framework: <any version-specific gotchas to record in `breaking-changes.md`>
- Performance: <any numbers to feed into the architecture's performance budgets>

## What lives on after this prototype
- This code is throwaway. Do **not** copy it into `src/`.
- The findings live on in <PRD path / ADR / concept doc update>.
- The questions answered are recorded above.

Ask: "Approve the report and write to prototypes/<name>/REPORT.md?"

---

Phase 8: Hand Off

Print:

"Prototype complete. Verdict: . <Recommended action — write a PRD, write an ADR, update concept doc, abandon, run another prototype>."

Update production/session-state/active.md:

• Note the prototype's verdict
• Pointer to next-action skill

Use AskUserQuestion:

• For YES: Update concept.md to retire the assumption, Author the PRD via /design-system, Author an ADR if a technical choice was validated
• For NO: Update concept.md with the new riskiest assumption, Run /brainstorm to find an alternative
• For INCONCLUSIVE: Run a follow-up prototype with a narrower question

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Phase 9: Anti-Patterns

The prototype is failing its purpose if:

• The code is being copy-pasted into src/
• The "prototype" took 2+ weeks
• The success criterion was not defined before building
• The team is treating the prototype as a feature
• The report is missing the verdict

If any of these, surface in the report's Notes section as a process learning.

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Quality Gates

• The Question is a yes/no
• Pre-defined YES and NO criteria are written before the build
• Verdict is YES, NO, or INCONCLUSIVE — never "the code works"
• Code lives in prototypes/, not in src/ or lib/
• Time spent is recorded honestly

---

Examples

/prototype gesture-during-session

• Question: Can users tap to log mid-activity without breaking flow?
• Stack: throwaway SwiftUI app
• 5 testers, 3-second target
• Median 2.4s, misfire 12%
• Verdict: YES
• Recommendation: write the PRD section confidently; the assumption is retired

/prototype ar-anchor-stability

• Question: Does ARKit hold the anchor through a 10-minute session?
• Stack: throwaway iOS app
• 1 device, 5 sessions
• Anchor drift average 0.8m at 10 min
• Verdict: NO
• Recommendation: drop AR anchor approach; explore alternatives. Update concept doc.