How privacy works here.
“Private” is easy to claim, so here is exactly what happens to your data — what runs locally, what is proxied, and what is stored where.
Analysis runs on your machine
Every evaluation — game review, the analysis board, and the engine you play against — comes from a Stockfish build running as WebAssembly inside your browser. Your moves, positions, and results are never sent to an analysis server, because there isn't one.
What is stored, and where
Review history, training puzzles, and preferences live in your browser's local storage on this device only. There are no accounts and no cloud copy. That also means the data is yours to lose: use Export dataon the Review page to back it up, and clear your browser's site data to erase everything.
What does leave your browser
- Username imports — when you look up a Chess.com or Lichess username, the request passes through a small proxy on our host (needed because those APIs block direct browser requests). The proxy forwards the username, returns the public games, and stores nothing.
- Puzzles — fresh training puzzles are fetched by your browser directly from the public Lichess puzzle API (falling back to a small proxy if that is blocked), then cached on your device.
- Share links— “Copy link” encodes the whole game into the URL itself. Nothing is uploaded; whoever opens the link re-runs the analysis locally in their own browser.
- Page-view analytics— the site uses Vercel's cookie-less analytics to count anonymous page views. It does not see your games, positions, or training data.
No account, by design
There is nothing to sign up for and no profile to build. The trade-off is honest: your training history doesn't follow you across devices unless you export it from one and import it on the other.
Questions about any of this? The whole app ships to your browser, so you can verify it in your browser's network tab: run a review and watch — no positions go out. Back to game review →