Things I build作品
Mostly tools I wanted for myself while learning Japanese, built and shipped under the name SlettvoldSec.
Oni Dojo鬼道場
A complete Japanese course from kana to JLPT N1, taught by Kurenai, a mischievous oni sensei. 140 guided lessons, over 15,000 voice recordings, spaced-repetition flashcards, graded stories, speaking practice and conversations you answer out loud. Out now on Google Play: kana and N5 free, Premium for N4 to N1.
WindowsAndroidElectron · Capacitor · Supabase
How it's built
- Offline first. Lessons, audio and progress live on the device. An account is optional, so most learners never send me any data.
- Purchases checked on the server. The phone buys through Google Play; an edge function asks the Google Play Developer API whether each purchase is real before anything unlocks, so patched stores can't fake Premium.
- Locked-down database. Row-level security on every table, no public write access to purchases or access levels, and accounts deleted with everything they own (GDPR).
- Signed updates. New lessons for the PC app are signed, and the app refuses anything that doesn't match its built-in public key.
- Voices recorded in advance. Every sentence is rendered with VOICEVOX at build time and checked against the app's own furigana, so the app never needs a speech server.
- Automated builds. GitHub Actions validates the content, runs syntax checks and builds the signed Android bundle for Google Play.
Rireki Studio履歴書
A free tool for foreigners applying for jobs in Japan. Fill in one form in English or Japanese and get a correct 履歴書 (on the 2021 government form or the classic JIS form) and 職務経歴書 as an A4 PDF. A checker catches about 30 common mistakes, such as old dates, abbreviations like ㈱, or more than 28 hours a week on a student visa, and a guide in 11 chapters explains every box.
Everything stays in your browser: no account, no server, no tracking. I made it for my own job search, and my own CVs were its first test.
WebVanilla JSPrint to PDFEN / 日本語Tokoyami Oni Radio常闇鬼電波
Japanese internet radio in one player: local and community stations from all over Japan, sorted by region, with the same neon oni look as my other apps. I listen to it all day for Japanese practice. It started as a Windows app and is now rebuilt natively for Android.
- Learn while you listen: programme titles translated or shown in romaji.
- Never miss a show: reminders before a programme starts, an alarm clock and a sleep timer.
- Small touches: volume per station, Chromecast, and a share card for what you're hearing.
Onibi鬼火
Coming soon
My next app: fuel prices near you, compared live on a dark map, with directions to the cheapest station. Prices come from official open data where countries publish it, and from drivers who report what they see at the pump.
It is in development now. Want to know when it's ready, or test it early? Send me a message.
Android (Kotlin, Jetpack Compose)SupabaseOpenStreetMapSecurity researchセキュリティ
Bug-bounty work through Intigriti: reconnaissance, attack-surface analysis and responsible disclosure. Details stay private, as they should.
This websiteこのサイト
Hand-written HTML on GitHub Pages, built by a small Python script: self-hosted fonts, a strict Content-Security-Policy that only runs scripts from this site, no cookies, no analytics and no third-party requests. The contact form posts straight to my own Supabase function in the EU.