How it works
One session, about 50 moves
A session is 5 minutes of focused training. You’re shown a real game position and your opponent’s last move, and you find the best move. A fresh position follows, until you’ve played about 50 moves or the clock runs out. The clock only runs while you’re thinking.
Every move scores
Stockfish runs in your browser and measures how much of your winning chance each move keeps. The best move earns close to 100 points; a move that gives something away earns less, in proportion to what it lost. You have 20 seconds per move, and no move in time scores 0. After each move you see the best move and why.
A session rating
Each position has a known difficulty. From the points you scored against them, the session solves for the rating that explains your results, with a plus-minus that shrinks the more moves you play. Sessions are scored the same way every time, so your rating is comparable from session to session.
Positions at your level
Positions come from the Lichess puzzle database. Your chess.com rating sets the starting point; after that, each position is picked near the level your session is trending toward. The summary at the end shows where you did well, where you lost the most, and the moves to look at again.