Tagbogen is an iPhone app for parents that records, with one tap, how long their children are outside. “Head out” starts the time, “Back inside” stops it, and the app adds it up per child against a daily goal the parent sets. It is built for everyday family life: a quick start from the Lock Screen, several children at once, and a gentle check-in when someone forgets to stop.
| Status | Live since November 10, 2026 |
| Availability | App Store, tagbogen.app |
| Name | Tagbogen |
| Genre | Family app for iPhone |
| Subsidiary | – |
| Time-to-Market Effort | 49 days from idea to the App Store (48 to submission) |
| Maintenance | Continuous, usage-driven development |
Project Highlights
- One tap to start and stop – in the app or from widgets on the Home Screen and Lock Screen.
- Up to six children: start together, stop one by one; a child can join later; the start can be moved back.
- Check-in instead of runaway timers: if an outing is still running, the app asks “Still outside?” – in the evening one hour after sunset, without location access; at night it stays quiet.
- Daycare and school: a template that the parent confirms with one tap; estimated time is kept separate from measured time.
- Progress: a daily ring per child, a run of days with rest days, a year grid, and a weekly or monthly report, also as PDF.
- Activity labels such as forest, playground or bike, optional per entry.
- Entries stay on the iPhone: no account, no ads.
- Accessibility: VoiceOver, Larger Text, Dark Interface, Differentiate Without Color Alone, Sufficient Contrast and Reduced Motion, as declared on the App Store.
- German and English.
- Subscription: yearly with a 14-day free trial for first-time subscribers, or monthly.
Technologies Used
- App: Expo with React Native and TypeScript, Expo Router, cloud builds with EAS.
- Widgets and notifications: Expo widgets for Home Screen and Lock Screen, locally scheduled notifications.
- Data: SQLite on the device; immutable events with device-generated UUIDv7 IDs.
- Time: value objects on top of the Temporal API; sunset computed from the time zone’s reference coordinate.
- Purchases: StoreKit through RevenueCat.
- PDF: generated on the device.
- Quality: about 1,400 automated tests including property-based tests (fast-check); dependency rules enforced in CI (dependency-cruiser).
- Website and help: static pages on Cloudflare Pages, no JavaScript, strict content security policy.
Architecture
The code is organized in bounded contexts – recording, progress, family, access and solar – around a shared kernel and an application layer. The aggregate is a single entry: one piece of outdoor time of exactly one child. Corrections are new events instead of overwrites, which keeps the history traceable and leaves room for sync later. Read models compute the day’s total as the union of time ranges plus confirmed estimates, so overlapping entries count once. 28 architecture decision records document the choices, from “Expo instead of native” to “PDF report on the device”.
Challenges and Solutions
- Time is hard. Outings cross midnight, time zones and the daylight-saving change. A range counts towards the day of the time zone in which it started and is split at midnight; durations are absolute. The DST night was tested on a real iPhone.
- Forgotten timers. A rule written before the code decides when to check in: at the earliest two hours after the start, in the evening one hour after sunset, at the latest after eight hours. Until the parent answers, an open time only counts up to the check-in.
- Privacy by design. Sunset comes from the time zone instead of GPS, and entries stay on the device. Restoring purchases brings back access, not data.
- Careful language. The app records time instead of following a child, and it makes no health claims. A separate review role checked all store and website texts against German medical-device and health-advertising law.
AI-Native Delivery
Tagbogen was built by Claude Code in 78 measured sessions and 288 merged pull requests, guided by four Claude chat roles for planning, organization, compliance review and marketing. My role was to define the product, decide, test on the device and approve every release. App Review approved version 1.0.3 without questions. The full story – timeline, division of labor, what was tight and the lessons – is in the workshop report.
Conclusion
Tagbogen shows that a small, carefully specified native app with subscriptions can go from idea to the App Store in 49 days – if the specification comes first and a human stays responsible for every decision.
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