Smart daily pack
Words banded by CEFR level, with a placement test to set the starting point.
Case study
10 words
A mobile vocabulary app built around one small, finishable habit: ten new words a day, a short daily quiz and a weekly exam built only from the days you completed.
I was responsible for the full build of the product: architecture, backend, mobile app, and deployment.
- React Native + Expo
- .NET 8 ASP.NET Core
- EF Core + SQL Server
- Firebase Auth
- Google Cloud Run
- Product
- Mobile vocabulary trainer for iOS and Android
- Role
- Everything: design, API, app, infrastructure
- Language pairs
- EN→PL · ES→PL · ES→EN · FR→EN
- Live
- 10-words.app ↗
The app in action
Language apps ask for too much
Endless courses and long lessons work until one busy day breaks the habit, and then the app gets abandoned.
- Sessions are too big to finish. A half-hour lesson loses to everything else in the day.
- Exams test words you never saw. Random question banks have nothing to do with what was actually studied.
- Reminders ignore the learner's day. A fixed server hour is wrong as soon as the user is in another time zone.
One small pack, one clear loop
The number is the product: 10 words a day, 3,650 a year.
- 1Morning pushAt your hour, in your time zone
- 2Draw 10Skip words you know
- 3FlashcardsTerm, translation, example
- 4Daily quiz5 choice + 5 typing
- 5100% = streakCounts toward Sunday
- 6Weekly examAfter 5 perfect lessons
Earned weekly exam
20 questions drawn only from the lessons you aced that week, in a 24-hour window.
Reminders at your hour
Daily, exam, streak-at-risk and birthday pushes, localized PL/EN.
Widget and offline mode
An iOS widget, plus cached screens that stay readable without a connection.
Scope of responsibility
Designed
- the rules of the daily loop and exam gating
- the data model and the REST contract
Built
- the .NET 8 API with background jobs
- the Expo app, widget and landing page
Delivered
- a Dockerized API on Google Cloud Run
- the landing site on Firebase Hosting
Architecture
Clients talk to one REST API. The API owns every rule and reaches the database and external services.
Mobile app
React Native + Expo · offline cache · iOS widget
Landing site
Firebase Hosting · email confirmation and reset page
HTTPS · Firebase JWT
REST API · ASP.NET Core (.NET 8)
- Identity
- Learning
- Words
- Notifications
Background jobs
Push scheduler · signup cleanup
EF Core · SDKs
SQL Server
Firebase Auth
Expo Push
SMTP
What was actually hard to get right
A weekly exam that follows the learner's clock
Problem. The exam must open on Sunday at each learner's own reminder hour, stay open for 24 hours and use only days they aced.
Solution. One service resolves the whole exam state per user, with the window computed from their time zone. The qualifying lessons are snapshotted when the exam starts, so later activity can't change its questions.
Drawing ten words that fit and never repeat
Problem. A pack has to match the learner's level and avoid every word already quizzed or skipped, even across redraws and half-finished days.
Solution. Selection excludes used and discarded words, fills the learner's level band first, blends in a couple of words from the next band and widens the range if the catalog runs thin.
What "today" means for every user
Problem. Packs, streaks, push hours and exam windows all depend on "the day", which differs per user and shifts with daylight saving.
Solution. Each user has a validated IANA time zone synced from the device, and all date logic goes through a single service. Streaks are evaluated lazily on read, so no midnight job is needed.
Push notifications without a queue
Problem. Send the right message at each user's local hour, never twice, and never let one bad account break the batch.
Solution. A hosted service polls every 15 minutes and skips anything already logged for that user, day and kind. A log row is written only for delivered pushes, so failures retry on the next tick.
Technical scope, in numbers
46REST endpoints
22,665words in 4 language pairs
4kinds of push notification
2background jobs
97localized API error codes