Building Neptune: From Idea to Full Web App in 3 Days

72 Hours. One Founder. A Full Product.

Three days ago, Neptune was an iOS app and an Apple Watch tracker. Today it's a complete web platform at neptune.coach — and the story of how we got here says something about what's possible in 2026.

Here's what shipped in 72 hours:

Day 1: Foundation

We started with a question: what if surfers could access Neptune from any device, not just iPhone?

By end of day one:

• Authentication — email, Google, and Apple Sign-In (shared user pool with the iOS app via Supabase)
• AI Coach on the web — the same Claude-powered coaching, now accessible from any browser
• 537 surf spot pages — every spot with real-time conditions, best conditions data, and embedded coaching

The spot pages were the SEO play. Each one is a landing page — someone Googling "Rincon surf conditions" lands on a page with live data, coaching, and a path to sign up.

Day 2: The Full Stack

Day two was about making the web app feel like a real product, not a marketing site with a chat widget:

• Stripe payments — Neptune Pro at $4.99/mo with a 7-day free trial
• Dashboard — live conditions for your favorite spots, just like the iOS home screen
• Favorites — heart any spot, synced between web and mobile
• Session logging — manual session entry (the Watch tracks automatically, but web users can log manually)
• Onboarding — skill level, home break, goals
• Settings & Profile — everything you'd expect from a real app

The key insight: web = top of funnel, mobile = retention. Get people in through the browser, let the Watch keep them coming back.

Day 3: Feature Parity & Polish

Today we shipped the remaining features that make Neptune... Neptune:

• Goals — set surf goals with progress tracking, coaching plans, and target date countdowns
• Neptune's Memory — the AI remembers your schedule, preferences, injuries, and coaching insights
• Surf Tape — upload photos of your surfing for AI technique analysis
• Crew — find surfers, plan sessions together, activity feed, friend stats

Four parallel AI agents built these simultaneously in under 30 minutes, each working on isolated files. Zero merge conflicts.

The Stack

For the technically curious:

• Frontend: Next.js 14, Tailwind CSS, deployed on Vercel
• Backend: Supabase (PostgreSQL, Auth, Storage, Edge Functions)
• AI Coaching: Claude API (Haiku for cost efficiency)
• Payments: Stripe (direct integration, RevenueCat sync coming later)
• iOS/watchOS: Swift, HealthKit, CoreLocation
• Development: Claude Code agents for parallel feature development

What's Next

The app is live. The web is live. Now it's about finding surfers who want a smarter way to track and improve their surfing.

If you surf and want an AI coach that actually knows you — your spots, your skills, your goals — come check it out at neptune.coach.

The first 5 coaching messages are free. No account needed. Just ask Neptune about conditions at your local break.

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We're building Neptune in public. Follow along on Instagram or try the AI coach right now.