Short version: no account, no ads, nothing sold. Your progress stays on your device. We measure how the app is used so we can make it better.
Your lessons, XP, streak and settings are saved in your browser's local storage. They never leave your device unless you clear them. If you use the Skepsis MCP server with an AI agent, progress is saved in a file on your own computer (~/.skepsis/progress.json).
The website uses PostHog (hosted in the US) to count visits and see how lessons go: which screens you open, which answers are right or wrong, how long a lesson takes, your streak and XP. Visitors are anonymous: we do not ask for your name or email and do not create person profiles. Session recordings are on, with everything you type masked. A weekly scoreboard shows XP next to a scrambled (hashed) version of the anonymous id, never a name.
Use a browser tracker blocker and the app still works. To erase your progress, use Settings › Reset progress, or clear this site's data in your browser. Questions: see Contact.
The code that does all this is public: github.com/ionpetro/skepsis.