Jack Dorsey, the name long associated with Twitter and Square, has entered an unexpected but fascinating phase in his tech journey. No longer confined to boardrooms and billion-dollar valuations, Dorsey has rolled up his sleeves and returned to building apps, this time with a bit of sunlight, a lot of code, and a healthy dose of what he calls “vibe coding.”
His latest project? A minimal yet cleverly designed health app called Sun Day is now available via TestFlight on iOS and is fully open-source on GitHub.
But Sun Day isn’t just a tool for tracking sun exposure and vitamin D. It’s a snapshot of the next era of app development, one driven by AI coding tools, personal creativity, and a throwback to hands-on, hacker-style building.
Sun Day: The App That Tracks UV, Vitamin D, and You
At its core, Sun Day helps users understand their UV exposure levels, giving insight into how long they can safely stay in the sun based on personalized data. It’s a lightweight app, but packed with functionality that connects real-world awareness with simple interface design.
Core Features Include:
- Live UV Index readings based on your location
- Environmental data such as cloud cover, sunrise/sunset
- Skin type selection from six categories
- Clothing input to adjust exposure estimation
- Manual session tracking to record time spent in the sun
- Vitamin D estimates based on exposure duration and sunlight intensity
Once you hit “Track UV Exposure,” the app begins timing your session. Ultimately, it calculates both your UV safety limits and the vitamin D gained during exposure. All data is generated on-device, using your phone’s GPS and weather APIs.
The twist? Users must manually toggle when they’re in and out of the sun, creating a hybrid experience that combines digital precision with analog input.
Vibe Coding: Dorsey’s New Development Philosophy
What truly separates Sun Day from other health-tracking apps isn’t just what it does but how it was made.
Dorsey describes his weekend coding projects as “vibe coding,” a style that combines curiosity, minimal planning, and letting intuition guide the development process. He’s not building with VC deadlines or quarterly goals. He’s building to learn. To explore. To vibe.
And he’s not doing it alone. Dorsey’s secret weapon is Goose, an open-source AI coding assistant that supports his journey from concept to code.
This combination of human creativity and machine guidance has created a weekend builder renaissance, a place where industry veterans and hobbyist devs alike can rapidly prototype ideas with little friction and complete control.
The AI Coding Tool Wars Begin
Dorsey’s use of Goose isn’t happening in isolation. It’s part of a much broader shift in how modern applications are being built and who’s fighting to control the tools.
Recently, OpenAI attempted to acquire Windsurf, a rival AI coding tool, in a reported $3 billion deal that ultimately collapsed. In a swift countermove, Google recruited Windsurf’s CEO and top talent to join its DeepMind division, underscoring that the race to dominate AI coding infrastructure is intensifying.
These tools aren’t just coding companions; they’re the next generation of productivity platforms, and the companies that control them could shape the very future of software development.
Why Sun Day Matters (Beyond UV Tracking)
While Sun Day’s features might seem modest on the surface, its implications are massive:
- Open-source codebase on GitHub invites collaboration and iteration
- AI-powered solo development shows how smaller teams (or individuals) can now compete with large orgs
- Focus on privacy and manual interaction nods to user autonomy rather than full automation
- Weekend-built, but production-ready—showing how fast ideas can ship in the AI era
In many ways, Sun Day is a proof of concept for a new kind of product development:
- Small, intentional, and fast
- Built with AI assistance
- Open to the world
It’s also an example of how tech leaders are returning to the joy of creation, not for profit, but for learning and self-expression.
A Cultural Shift in Software Development?
Dorsey’s vibe coding mindset mirrors a larger cultural pivot in tech. With AI tools becoming more accessible, more developers are starting to experiment again. They’re building tools not for business, but for themselves. For fun. For curiosity.
Just like the early days of the web.
In a time when AI threatens to commodify creativity, Dorsey’s low-key projects remind us that software can still be personal, playful, and purposeful all at once.
Final Thoughts from Blockrora
Jack Dorsey’s Sun Day may not be a billion-dollar app, but it doesn’t need to be. It’s a beacon for where development is headed:
- AI-augmented coding
- Open-source collaboration
- Human-centered design
And most importantly, it’s a call for builders just to build, trusting their vibes, write some code, and put something useful (or delightful) into the world.
In an industry dominated by scale and metrics, Dorsey’s Sun Day is a small but powerful rebellion.
