Last updated: 8 September 2026
Who runs this site
korczak.xyz is a personal site run by Oskar Korczak. Anything on this page can be asked about at oskar.jan.korczak@gmail.com.
What the public pages collect
Nothing. The blog, the songbook, the course notes and the rest of the public pages carry no analytics, no advertising and no third-party tracking scripts. The visitor counter in the footer is a decoration from 1997 and counts nobody.
The apps keep their data in your browser
The small apps — the typing trainer, the guitar flashcards, the tuner, the sleep log, the games and the others — store what you do on your own device, in your browser’s local storage. That copy stays on the device and is sent nowhere unless you sign in.
Signing in
Signing in uses Firebase Authentication with an email address and a password. It exists for my own accounts rather than as a public sign-up. While signed in, app data — typing progress, flashcard schedules, sleep-log entries, notification subscriptions and diagnostic logs — syncs to Google Cloud Firestore in the project korczak-xyz-501720, so it survives a lost device and reaches another one. Google holds it as the hosting provider; nobody else receives it, and none of it is sold, shared or used for advertising.
Notifications
If you turn notifications on in one of the apps, your browser creates a push subscription, and its address is stored with your account so a scheduled job can deliver the alert. Turning notifications off removes it.
Hosting
Cloudflare serves the site and sees what any web server sees — your IP address, the page you asked for, your browser’s user agent — and uses it to deliver pages and to block attacks.
Your data and your choices
Clearing your browser storage removes the local copy of everything the apps hold. To ask what is stored under an account, or to have it deleted, write to oskar.jan.korczak@gmail.com. If this page changes, the date above changes with it.