How I Built a Full App Solo in 3 Weeks

January 15th. I open the RevenueCat Shipyard brief. 28 days to build something real.

February 9th. Muse Otter is live — 6 AI companiones, voice input, custom coach creator, subscription system, iPad-native design, and full localization.

Here’s how.

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The Timeline

Week	Focus	Deliverables
Week 1	Foundation	Auth, data models, default coaches, basic chat
Week 2	Core Features	Voice input, custom coaches, Know You context
Week 3	Polish	iPad UI, Foundation feature, onboarding, paywall
Week 4	Ship	Testing, docs, marketing assets, submission

I didn’t plan it this clean. It just happened because I’ve done this before.

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The Stack That Made It Possible

Every choice was about removing decisions:

Frontend:     Flutter 3.24 (one codebase, 6 platforms)
State:        Riverpod (code-gen, type-safe)
Backend:      Firebase Cloud Functions v2 (zero ops)
Database:     Firestore (real-time, offline)
AI:           Genkit + Gemini 2.0 Flash
Payments:     RevenueCat (handled in hours)
Voice:        Vapi SDK
i18n:         Slang (code-gen translations)

Why Flutter? One codebase for iOS, Android, Web, and macOS. iPad isn’t a stretched phone UI — it’s a proper three-column layout.

Why Firebase? I don’t want to manage servers. Cloud Functions scale automatically. Firestore handles offline sync. Auth handles everything from anonymous to Google Sign-In.

Why RevenueCat? StoreKit and Google Billing would have taken a week each. RevenueCat took an afternoon.

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The Process

Day 1-3: Auth + Data Model

Started with the boring stuff:

• Firebase Auth (anonymous first, link account later)
• Firestore structure (users, coaches, chats, messages)
• Basic Riverpod providers

Day 4-10: Make It Work

• Chat interface with real-time updates
• AI pipeline (Genkit → Gemini → Firestore)
• 6 default coaches with distinct personalities
• Know You context system

Day 11-17: Make It Good

• Voice input with Cloud Speech-to-Text
• Custom coach wizard (4-step creation flow)
• iPad-native responsive design
• Foundation feature (personal growth tracking)

Day 18-21: Make It Ship

• RevenueCat integration
• Paywall screens (soft + hard)
• Onboarding flow with celebration animations
• Localization (EN + FR)
• Testing, bug fixes, polish

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Key Decisions

1. Anonymous Auth First

No signup friction. Users can chat immediately. Account linking comes later if they want to sync across devices.

Result: Zero drop-off at onboarding.

2. Document-Status Pattern for AI

Instead of WebSockets or complex streaming:

1. User sends message → status: "pending"
2. Cloud Function triggers
3. Genkit calls Gemini
4. Response written → status: "done"
5. App updates via Firestore listener

Simple. Reliable. Debuggable.

3. Feature-First Architecture

Every feature is self-contained:

lib/features/chat/
├── data/           ← Firebase integration
├── domain/         ← Business logic
└── presentation/   ← UI + Riverpod

No cross-feature dependencies. I can work on one thing at a time.

4. iPad as First-Class Citizen

Most apps treat tablets as an afterthought. I built a three-column layout from day one:

Phone:  Chat only
Tablet: Coaches | Chat | Context

It’s not harder. It just requires thinking about it early.

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What I Shipped

• 6 AI Coaches with distinct methodologies
• Know You personal context system
• Foundation personal growth journal
• Custom Coaches with AI-assisted creation
• Voice Input via Cloud Speech-to-Text
• Voice Calls via Vapi (real-time AI conversations)
• Subscription System via RevenueCat
• iPad-Native responsive design
• EN + FR localization

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The Real Secret

I’ve built 3 structured reflection apps before this one. BeeDone. Evolum. Strive.

Every app makes the next one faster. Not because I copy code — I don’t. But because I know what works:

• Document-status pattern for AI
• Anonymous → linked auth flow
• Feature-first architecture
• RevenueCat from day one

The first time I built a reflection app, it took 6 months. Now it takes 3 weeks.

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Try It

Muse Otter is free to start. 20 messages per day, no credit card.

If you’re building something and want a sounding board at 2am, give it a shot.

That’s what I built it for.