Sumi
iOS app for learning to read and write Japanese kana and JLPT N5 kanji. Adaptive quiz, handwriting feedback, full offline mode. No account, no ads, free.
- Year
- 2026
- Role
- Solo creator
- Duration
- ~2 months of work
- Team
- Solo
- Links
- Website↗
Context
I wanted to learn hiragana, katakana and the first kanji to pass my JLPT N5, but no free app on the market was both pleasant to use and ad-free. So I built my own: polished, offline, no account, no ads.
What I did
- App architecture (Expo Router, Zustand, MMKV) with Zod-validated rehydrate and store migrations
- Handwriting recognition pipeline (DTW on KanjiVG paths) with per-stroke scoring and replay
- Custom SM-2 SRS with soft lapse and adaptive question-type biasing
- Automated tests on business logic (SRS, selectors, question picker, stroke matching)
- Visual language: ink palette, dark-only theme, Outfit + Noto Sans JP typography
Results
- Shipped to the App Store as a solo developer, fully offline, no tracking, no IAP
- Covers all kana plus 80 JLPT N5 kanji, usable as a single N5 prep tool
- Shipped a complete iOS app from design to App Store as a solo developer in ~2 months
- Handwriting recognition runs fully on-device, no third-party SDK, no cloud call
- Onboarding gets a user reading their own name in katakana within 60 seconds
Key features
- 107 hiragana + 107 katakana + 80 JLPT N5 kanji, with stroke-order animations and Japanese TTS audio
- Adaptive daily quiz across 4 question types: recognize, compose, trace, listen
- Real handwriting feedback: each trace is scored per stroke, with a single-stroke replay on misses
- "Reading reveal" after each session: the words and sentences your mastered kana now unlock
- 60-second magic onboarding: type your name, see it in katakana, trace the first character
- Sumi Paper free canvas, Story Mode, mnemonics, confusion drill, weekly streak shield. 100% local, no account, no ads, no IAP
Stack
