Reza Bina

iphone apps, built and shipped · berlin

ZumNum

Learn German numbers by ear · shipped 2025-08-01

what it does

German numbers are said back to front — 5 716 is “fünftausendsiebenhundertsechzehn”, with the units before the tens — so reading them is one skill and hearing them is another. ZumNum drills the second one: it speaks a number aloud, you type what you heard, and it tells you immediately whether you caught it. The voice is synthesized on the device, so the whole thing works offline, with no ads and no account.

how it works

Hear it, type it
A neural voice speaks a number; you type the digits and find out instantly whether you got it right — and if not, what it actually was.
It learns what trips you up
Every answer updates a running score per digit length and per German quirk — the swapped units and tens, the teens, an internal zero. Later rounds drift toward the patterns you keep missing, while still revisiting the ones you have mastered.
A result that means something
The end of a round names a genuine strength and one attainable next step, drawn from your own history rather than a percentage. On iOS 26 that sentence is written on-device by Apple Foundation Models; everywhere else a deterministic version says the same thing.
The voice runs on your phone
Speech is synthesized locally by an on-device neural model — no request leaves the device, and it works with no connection at all.
Private by design
No accounts, no tracking, no ads. Nothing you do leaves your phone.

stack

built with
SwiftUI
Swift 6 Concurrency
On-device neural speech
Apple Foundation Models
Fully offline
iOS 17+

writing

2026-07-28 The state machine that runs both my apps read →
2026-07-27 How I moved ZumNum from Combine to Swift Concurrency read →
2026-07-26 Why I build apps that can't see your data read →

screens

ZumNum marking an answer correct: a cartoon avatar above a "Correct" speech bubble and the number 7334.
Answer, then immediate feedback.
ZumNum start screen on ruled-paper lines, headed "Ready to Catch Some German Numbers?" with a Let’s Practice button.
Handwritten on ruled paper — the whole app has one voice.
A round in progress: the avatar with a play button and the instruction to play the audio and listen carefully.
Each round starts with a number spoken aloud.
The answer step: "Enter what you heard!" above a numeric field and a Check button, with the number keypad open.
Type what you heard — digits only, no spelling.
A wrong answer showing the entry 5760 and a bubble reading "Wrong! It is 5.716".
A miss shows the real number, so the gap is obvious.
End-of-round screen: 11 out of 12, the title "Unstoppable!", and a message about recognizing single digits and mastering the tricky teens next.
The closing note is personal — a strength, then a next step.