Jack Dorsey, the guy who helped build Twitter and runs Block, is back at it again. Only this time, he’s not launching another social media platform or crypto project.
No, no. He’s cooked up an app called Sun Day that tracks how much sun you’re soaking up. It’s like your personal sun-counting consigliere, keeping tabs on your vitamin D hustle.
track your (vitamin) D
a Sun Day app for Sunday.https://t.co/KKsq3LkLEj
— jack (@jack) July 13, 2025
The plan D
Before Sun Day, most of us just eyeballed the sun, maybe guessed if we’d had enough rays or slapped on sunscreen like a shot in the dark.
No science, no data, just hope and maybe a little sunburn. Dorsey’s new app changes the game by using some fancy AI magic, built with Block’s assistant, Goose, to calculate your vitamin D synthesis based on UV exposure.
And it’s not just guessing, it’s science-backed, factoring in your location, age, skin tone, and even what you’re wearing. Like a wise capo knowing every detail before making a move.
Customization
Sun Day launched quietly last Sunday on Apple’s TestFlight, meaning it’s in beta, still in the lab, getting tested by the early birds before it hits the big stage.
You gotta manually tell the app when you step outside and when you come back indoors.
No sneaky automatic light sensors here, Dorsey’s keeping it old school with a manual on/off toggle. It’s like calling your guy when the job’s done, no surprises.
The app even pulls in data from Apple Health and your past vitamin D records to fine-tune its estimates.
And it’s playing it safe, keeping the numbers conservative so you don’t end up with a sun overdose.
Future upgrades? They’re cooking up plans to add height, weight, seasonal changes, and even your actual blood vitamin D tests. Talk about leveling up.
right now it logs as soon as you stop. running in and out is marginal overall, so i cut pause for now.
— jack (@jack) July 13, 2025
Track health
The funny part is thta this is Dorsey’s second app in two weeks. Just last weekend, he dropped the beta for Bitchat, a decentralized, Bluetooth-powered messaging app.
No internet, just pure peer-to-peer chatter. When asked if he’s flooding the market to see what sticks, Dorsey shrugged it off, and said he’s learning.
That’s right, he’s experimenting, tinkering, and using AI assistant Goose to build these projects like a boss honing his craft.
In fact, Jack’s redefining how we track health and communicate, blending tech with real-world needs.
It’s like watching a seasoned capo take the reins, learning every angle before making the big move.
So next time you’re outside, soaking up those rays, remember, Sun Day might just be the partner you didn’t know you needed.
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