Jack Dorsey Launches Sun Day: An AI-Powered App for Tracking Vitamin D Exposure

Now Jack Dorsey has built an app to track your vitamin D

Dominic Preston is a news editor with over a decade's experience in journalism. He previously worked at Android Police and Tech Advisor. Twitter co-founder Jack Dorsey has released a new app that tracks your sun exposure and vitamin D levels. It's his second app in a week, after last weekend's encrypted peer-to-peer messaging app Bitchat. Sun Day is available now for iOS via TestFlight, and the code for the project is available on GitHub. The app uses location-based data to display your local UV index and sunlight hours. You can detail your skin type and clothing level, then manually toggle when you're in and out of the sun and the app will track your rough vitamin D levels for the day, along with how long you can be in direct sunlight without burning. Dorsey says he's "learning" through his recent weekend coding projects, which he's developing using the open-source AI coding tool Goose. It and similar vibe coding tools are one of the next key battlegrounds for tech's AI giants -- just last week a $3 billion deal for OpenAI to buy AI coding tool Windsurf fell through, as Google swooped in to hire Windsurf's CEO and top talent onto its DeepMind team.

Jack Dorsey Drops His Second New App in a Week

The Twitter founder says he used AI and â€~vibes’ to build both apps. Jack Dorsey is shipping. On Sunday, the Twitter co-founder shared a link on X (formerly Twitter) to a new app called Sun Day, which he claims helps users track their vitamin D intake. It's the second new app he's debuted in a week, and it's all thanks to the help of AI. Sun Day calculates how long users can safely soak up the sun before burning their skin using the UV index of the user's location, cloud cover, sunrise and sunset times, skin tone, and even what kind of clothes they’re wearing. This feature is no doubt helpful to people like Dorsey, who casually mentions later in the thread that he does not use sunscreen. The app also tracks a user’s time outdoors to supposedly estimate how much vitamin D they’re absorbing. This is based on “UV exposure using a multi-factor model based on scientific research,†according to the app’s GitHub page. Just how accurate that model is remains unclear. Future updates will improve calculations with factors like height, weight, and the user's actual vitamin D blood levels. For now, anyone who is curious can try Sun Day themselves on iOS via TestFlight or poke around its code on GitHub. Like Dorsey’s other recent "weekend project,†BitChat, Sun Day was built using Goose, the AI coding assistant developed by Block, Dorsey’s payments company. And both projects are part of a broader trend Dorsey seems into right now, “vibe coding.†Vibe coding is a newish approach where developers rely heavily on AI assistants to generate and debug code using natural language prompts. This allows developers to focus more on the overall “vibe†of what they're trying to accomplish with an app rather than the technical specifics of its code. The previous Sunday, Dorsey announced the beta launch of BitChat, a messaging app built for peer-to-peer conversations over Bluetooth mesh networks instead of the internet that does not require any phone numbers, emails, or any permanent IDs to function. “[B]itchat addresses the need for resilient, private communication that doesn’t depend on centralized infrastructure,†Dorsey explained in a white paper published to his GitHub page. “By leveraging Bluetooth Low Energy mesh networking, bitchat enables direct peer-to-peer messaging within physical proximity, with automatic message relay extending the effective range beyond direct Bluetooth connections.†But BitChat has already run into skepticism. In a recent blog post, Supernetworks CEO Alex Radocea pointed out a major flaw: the app does not currently have any real way to verify who a user is talking to. “In cryptography, details matter,†Radocea wrote. “A protocol that has the right vibes can have fundamental substance flaws that compromise everything it claims to protect.†Since the blog post, the app’s GitHub page has added a warning stating that the app “has not received external security review and may contain vulnerabilities and does not necessarily meet its stated security goals.â€Â It's just a reminder that vibecoding might be a way for developers to brute-force their way to a functional product, but users might want to think twice before installing these apps and taking on the potential security risks.

Jack Dorsey's new app tracks how much grass you're touching

Sun Day is the second app that the Twitter co-founder has launched in the last week, and it was built using Block's artificial intelligence assistant, Goose. Block CEO and Twitter co-founder Jack Dorsey has launched a new app that gives users a rough idea of how much exposure they've had to the sun. Dorsey shared the "Sun Day" app to his followers on X on Sunday, which, according to its white paper on GitHub, "calculates vitamin D synthesis from UV exposure using a multifactor model based on scientific research." It is available through Apple's TestFlight app, which allows developers to test beta versions of their apps and App Clips to get feedback from users before an official release. The app uses location services to track the current UV index and estimate sun exposure based on the user's location. It also asks for input on age, type of clothing being worn and individual skin tone. It also factors in other data from the Apple Health app and historical data such as HealthKit vitamin D records. "The app aims to provide personalized, accurate estimates while remaining conservative for safety," its white paper states. The app requires a user to input data manually. Users will need to tap a button when they're exposed to the sun and again once they are back indoors. "[...] doesn't look for light. It's a manual on/off toggle," Dorsey said in response to a user's question on X, explaining to another that the app logs after each session. There are also several improvements flagged for the future. The white paper lists using more precise calculations based on height and weight, along with seasonal adjustments and the user's actual vitamin D blood tests as possible updates. Last weekend, Dorsey launched the beta version of a new decentralized peer-to-peer messaging service known as Bitchat, which runs entirely over Bluetooth. At the time, he said his weekend was spent learning about "Bluetooth mesh networks, relays, store and forward models, message encryption models, and a few other things." Related: Jack Dorsey pushes Signal to adopt Bitcoin payments In a post on Sunday, Dorsey told a user who asked if the app launches were part of a plan to flood the market and see what sticks that "Nah. I'm learning." He also revealed that he was using Block's artificial intelligence assistant, Goose, to create the apps.

After Bitchat, Jack Dorsey unveils new app to track sun exposure and vitamin D levels, here's how it works

Developed using AI coding tool Goose, the app's code is available publicly on GitHub. Ask ChatGPT Twitter co-founder Jack Dorsey has introduced yet another application that can track sun exposure and estimate the vitamin D levels in the human body. Dubbed Sun Day, the app aims to better understand the user's health. The Sun Day app is currently under testing and is available for iOS via TestFlight. The app uses location-based data which helps in displaying the exact local UV index and sunlight duration. All the user needs to do is input their skin type and clothing coverage, and manually toggle their sun exposure throughout the day. After processing all this data, the application will make an estimate of how much Vitamin D the user may have generated and how long they can stay in direct sunlight without burning. This is an open-source project with the code published on GitHub. As per the reports, Dorsey and his team made the application Goose, which is an AI-based coding tool. He described the project as part of his learning process, experimenting with solo development using open-source AI tools. Also read: Vivo X200 FE and X Fold 5 launched in India: Check price, specs, availability and more This comes amid the growing interest in AI-assisted development tools. Many tech giants including Meta, OpenAI, and Google have been hiring and forming AI teams as a part of their long-term strategy. Meanwhile, Jack Dorsey also introduced a new application called Bitchat, a decentralised, peer-to-peer messaging app that works without the internet using Bluetooth Low Energy mesh networking. Currently in beta via TestFlight, it requires no registration or servers, supports encrypted chats, and is designed for anonymous, offline communication in remote or emergency situations. However, the details about the official details about the public are under wraps and it has a current test limit of 10,000 users. The app may also expand support for more platforms, claims a report.