The short version is short because the app is simple.
Your progress lives in your own browser. There are no accounts, no ads, and nothing personal is collected or sold.
Everything you do here, which lessons you've finished, your self-ratings, your practice days, your goal, is saved in your browser's local storage. It never leaves your device and it isn't sent to us or anyone else. Clear your browser data and it's gone; we have no copy.
To know whether the app is actually helping people, we use Plausible, a privacy-friendly analytics tool. It counts anonymous things like page views and which lessons get completed. It does not use cookies, does not track you across other sites, and does not collect anything that identifies you personally.
No sign-up. No email. No advertising. No selling data, because there's no personal data to sell. If that ever changes, for example if accounts arrive so your progress can sync across devices, this page will change first and say so plainly.
This is an independent project. If something here is unclear, the answer is almost always "it stays in your browser."