Bronzla tells you how long you can safely stay in the sun, based on your skin type and the live UV index. It is a free iOS and watchOS app, built for Türkiye first.
No account. No ads. No subscription. No in-app purchases. No analytics SDKs.
Download on the App Store · bronzla.app
Bronzla is not a medical device and does not give medical advice. It estimates sun exposure limits from published dermatological guidance and a live UV index, and those estimates carry real uncertainty. No app can tell you that a given exposure is safe for you specifically. People with photosensitivity, a history of skin cancer, or medication that affects UV sensitivity should speak to a doctor rather than rely on this.
Every constant in the exposure model traces to a published source. Those sources are listed in docs/EXPOSURE-MODEL.md and are reachable from inside the app on every screen that gives guidance. Where a figure is the app's own estimate rather than published data, it says so, in the code and in the interface.
- A sun timer driven by your Fitzpatrick skin type, the current UV index and your sunscreen SPF, with flip and reapplication reminders.
- Hourly and ten day UV forecasts, charted.
- Session history and a discipline score that rewards staying inside safe limits rather than maximising time in the sun.
- Family profiles, so one phone can track several people.
- An Apple Watch app, home screen widgets and a Live Activity.
- Full Turkish and English localisation. Turkish is the source language.
App/ Xcode project and all five targets
Bronzla, BronzlaWatch, BronzlaWidgets, BronzlaTests, BronzlaUITests,
plus Shared/ and Config/
backend/ AWS CDK stack for Sign in with Apple and the global leaderboard
site/ bronzla.app, an Astro static site deployed to Cloudflare
docs/ Architecture and the exposure model
tools/ Standalone developer utilities
The Xcode project lives inside App/ alongside every folder it references, so all paths in
project.pbxproj are relative and the project can be moved as a unit.
Requires Xcode 26 or later, and an iOS 18.0 or later simulator runtime.
cd App
xcodebuild build -project Bronzla.xcodeproj -scheme Bronzla \
-destination 'platform=iOS Simulator,name=iPhone 17 Pro'
Tests:
cd App
xcodebuild test -project Bronzla.xcodeproj -scheme Bronzla \
-destination 'platform=iOS Simulator,name=iPhone 17 Pro'
The unit suite is 129 tests across 14 suites, written with Swift Testing. Note that
xcodebuild prints Executed 0 tests from its legacy XCTest reporter, because there are no
XCTest cases; read the Swift Testing summary instead.
WeatherKit will not return data in a fork without your own Apple Developer team and a WeatherKit-enabled App ID. The app is built so this does not block you: every weather-backed service is behind a protocol with a sample implementation, so previews, tests and offline use all work without a WeatherKit entitlement. See docs/ARCHITECTURE.md.
The CDK stack in backend/ is complete and unit-tested, but the shipped 1.0 build points at a
placeholder URL, so the global leaderboard is inert in the released app. Everything else,
including the on-device family leaderboard, works fully offline. This is stated plainly rather
than glossed, because a repository that implies a running service it does not have is worse
than one that admits the gap.
Location never leaves the device. Coordinates are rounded to two decimal places before being
used as a cache key, which is roughly a kilometre of precision, enough to cache a UV forecast
and not enough to identify a home address. Sign in with Apple is optional and gates only the
global leaderboard. Session tokens are stored in the Keychain, scoped to one device, never in
UserDefaults.
See CONTRIBUTING.md. The short version: changes to ExposureCalculator
need a cited source and a test, because that is the code that can burn someone.
To report a security issue, see SECURITY.md. Please do not open a public issue for anything security related.
Licensed under the Apache Licence, Version 2.0. See LICENSE and NOTICE.
"Bronzla" and the app icon are trademarks of HMD Developments and are not covered by that licence. You may fork and redistribute the source, but not under the Bronzla name or icon.
Built by Umut Güden, on behalf of HMD Developments.