Health, home and travel decision
Bask
A competent developer can build a useful personal sun/ vitamin-D tracker (timer, UV lookup, local history) in a multi-week effort, but reproducing Bask's polished iOS integrations, App Store UX, and paid/subscription polish is nontrivial; an existing open-source tracker (jackjackbits/sunday) lowers the barrier for a narrow replacement.
View on the App Store↗$4.99/mo
$60/yr
Read off the official pricing page.
$100one-off50 h to build
$10/mo3 h/mo upkeep
On cash alone, building overtakes the subscription at 4 seats.
Open-source builds that already do this
Every project below is open source and already does this job today. Fork one, self-host it, or take the parts you need - the build prompt further down assumes an empty file, and this is the shortcut past that. Licences differ; check the one on each card before you ship. All Bask alternatives, with the arithmetic →
What a replacement has to do
- Open device location and UV API → compute vitamin D yield for a session → start/stop sun-timer with time-to-sunburn guidance → record session to local store and show history/trends → schedule notifications for best sun windows
What it still won’t have
- Polished App Store UX, onboarding and marketing
- Built-in Live Activities / deep iOS integration quality
- Optional leaderboard / social features and any proprietary algorithms
- Ongoing polish and cross-device testing performed by a dedicated team
What remains hard
- Product polish and ongoing maintenance
First-year cost
Keep paying
Paying is—cheaper in year one.
On cash alone, building overtakes the subscription at 4 seats.
Money you would actually spend
Time you would spend
—
What you would spend
What we assumed
The verdict above measures whether you could build it. This one is only about money.
Runnable build prompt
Build a minimal cross-platform mobile Vitamin D sun tracker using React Native (Expo) plus a small Node/Express backend only if needed. In scope: (1) iOS/Android app that reads device location, queries a public UV/UV-index + weather API, and shows current UV and 48-hour forecast; (2) implement a vitamin-D calculation routine that accepts skin type, clothing, SPF, and duration and returns estimated D yield and time-to-sunburn; (3) start/stop sun session UI with a live timer and local persistence (SQLite or AsyncStorage) of sessions, supplements, and lab entries; (4) charts for 7/30/90-day trends; (5) local notifications and scheduling for best sun windows; (6) basic privacy: store data locally and provide an option to export; (7) automated unit tests for the calculation routine and end-to-end tests for session flows; (8) CI to build app bundles and instructions for App Store submission. Out of scope: polishing UI/animations, leaderboard/social features, advanced Live Activities implementation, paid subscription billing integration. Include error handling for network failures, permission denials, and invalid inputs; include tests for edge cases in the vitamin D algorithm.
How we checked
How the score was reached
- Partly verdict base52
- An open-source build was found+5
- 2 cited sources+1
- Price verified on pricing page+3
- Evidence score61
The base comes from the verdict. Everything under it is a check that either happened or did not, and each one is a fact frozen in this record rather than a judgement made at render time - so the same evidence always produces the same number.
How scoring works →Cited sources · 2
Every page the run actually retrieved.
- official productVitamin D Sun Tracker - Bask App - App Store
- open sourcejackjackbits/sunday
Integrity checks
What held up, and what did not.
