SunUp by GearTOP
Personalized UV safety app that calculates your real burn time based on skin type, live UV index, and cloud cover. Features 48-hour UV forecasts, family mode for multiple profiles, AQI tracking, and sun protection product recommendations. Built as a non-coder using AI-assisted development.
- Live in the App Store since September 2025
- Covers UV Index, AQI, burn time calculation, and family profiles
- Integrates real-time UV and air quality data via location services
- Built for GearTOP's sun protection product line
The problem
GearTOP sells sun protection — hats, balaclavas, UV gloves. The people buying them are hikers, anglers, and parents at the beach, and every one of them is making the same decision badly: how long can I actually stay out here?
The UV index alone doesn’t answer that. A UV index of 7 means something very different to someone with fair Northern European skin than to someone who tans easily. Cloud cover changes it. Time of day changes it. And the answer for a 40-year-old is not the answer for their four-year-old.
Every UV app I looked at either dumped a raw index number on you, or buried the useful part behind a subscription wall.
What it does
SunUp takes six inputs — Fitzpatrick skin type, live UV index, cloud cover, time of day, location, and whether sunscreen has been applied — and returns one number: minutes until you burn. That’s the whole product.
Around that core it adds:
- 48-hour UV forecast, so you can plan the hike rather than react to it.
- Family mode — separate profiles, because the burn time that keeps you safe will not keep a child safe.
- Air quality (AQI), which turns out to matter to the same people on the same days.
- Gear recommendations tied back to GearTOP’s actual product line.
How it was built
React Native and Expo, scaffolded in VibeCode, with Claude Code doing the heavy lifting on logic and API integration. I do not have a software development background — I’m a mechanical engineer who spent 22 years in industrial equipment design.
What made it possible wasn’t that AI writes code. It’s that AI closes the gap between knowing what the thing should do and having a working build to test. I could specify the burn-time model precisely, because that part is just physics and dose response. The part I couldn’t do — turning that into a shipping iOS binary — is the part that used to cost $50,000–$70,000 and six months of somebody else’s calendar.
What I’d tell someone attempting the same thing
The build is not the hard part any more. The App Store is. Getting a first app through review taught me more about shipping software than writing it did — see the RunMate Pro story, which took 39 rejections.
The other lesson: an app attached to a product business has a job beyond downloads. SunUp exists because it makes GearTOP’s customers better at the thing they bought the product for. That’s a durable reason for it to exist, and it’s why it isn’t chasing subscription revenue.