Privacy
Your data lives on your device, and syncs so you don't lose it. Games, repertoires, and practice history are stored in your browser. When you connect Lichess, your repertoires, practice history and preferences also sync to our server so your phone and computer stay in step — and so a cleared browser doesn't cost you your prep.
What we store
Your public Lichess username (and chess.com username if you link one), your opening prep, and your practice history. That's it — no email, no password, and never your Lichess credentials: sign-in is OAuth with a scope-less token that can only read public data. Your games are not stored on our server; each device fetches them straight from Lichess/chess.com's public APIs. The person who runs elo9000 can access synced data when debugging.
Cookies and tracking
No cookies, no ads, no cross-site tracking, no fingerprinting. We use privacy-preserving, cookieless analytics (Cloudflare Web Analytics) that count visits, not visitors — no personal data is collected and nothing is shared with advertisers. Our host (Netlify) may also produce aggregate, cookieless traffic statistics from its server logs.
Your data, your call
Export any repertoire (with its full practice history) as a JSON backup from the app. In Settings you can see every signed-in device and sign any of them out. Want everything our server holds about you deleted? Ask, and it's done — completely. Disconnecting Lichess keeps your local data; it just signs you out.