Jack Dorsey, co‑founder of Twitter and Block, has launched Sun Day—an iOS app that helps users monitor their daily UV exposure and estimated vitamin D intake. The app uses the user’s location, skin type, and clothing coverage to offer personalized insights on safe sun exposure and vitamin D levels throughout the day
🔍 4 Key Features
1️⃣ UV index & sunlight tracking
Sun Day fetches local UV index, sunrise/sunset, and cloud cover using location-based data, letting users manually log when they step into or out of the sun
2️⃣ Personalized vitamin D estimates
By tracking skin type (six categories) and clothing coverage, Sun Day estimates vitamin D synthesis and safe exposure times to avoid skin burn The Verge.
3️⃣ HealthKit integration
The app is integrated with Apple Health, allowing tracking of vitals like age, past vitamin D readings, and syncing data for a holistic health record
4️⃣ Open-source & built via AI
Developed using Block’s AI coding tool “Goose,” Sun Day is open-source and available to download via TestFlight and GitHub, showcasing Dorsey’s weekend “vibe coding” learning approach
🔭 Why It Matters
- Health meets AI: The app highlights how AI-powered tools can streamline personalized wellness.
- Vibe coding spotlight: Dorsey exemplifies rapid app creation powered by AI assistants like Goose rather than traditional IDEs .
- Wellness trend: Sun Day aligns with a growing market for digital health tools focused on preventive care.
- Developer transparency: Public code access encourages community-driven improvements and trust.
✅ Bottom Line
With Sun Day, Jack Dorsey leverages AI-driven “vibe coding” to deliver a lightweight, open-source wellness app focusing on safe sun exposure and vitamin D tracking. Available on iOS TestFlight, the app reflects Dorsey’s experimental weekend projects and signals a growing interest in health‑tech innovation.
