Chessility FAQ
The short version of how this chess trainer works — ladder, best moves, and threats.
What is Chessility?
Chessility is a free chess trainer in the browser. You play Stockfish bots, see the engine’s best move, and get a threat highlight when something of yours is hanging. There are no accounts — progress stays on your device.
How does the opponent ladder work?
Start with Plankton (~400). Win 3 games against a bot at or above that bot’s accuracy line to unlock the next one, up to The Auditor (~2200). The line starts at 70% and rises as the bots get stronger. Beaten bots turn green on the opponents page.
What does “best move” mean?
The best move is Stockfish’s single top choice for that position. It is great when the next choice gives away real ground, and brilliant when that choice also leaves a piece hanging and still works. Another move is excellent or worse, even when it keeps a win. Excellent moves count as half a best move. Inaccuracies, mistakes, and blunders count as zero. A best move played from a hint does not count toward accuracy.
How is accuracy scored?
Accuracy is (best moves + half of excellent moves) divided by your moves, as a percent. A best move played from a hint adds nothing. It is stored locally with your best win against each bot. Only wins at or above the bot’s accuracy line count toward the next unlock.
What does “spot the threat” mean?
After the bot moves, Chessility waits a few seconds, then can highlight the engine’s next punch if you ignore the position: a hanging piece, a winning capture, or a check. Checks show a little sooner. Answering that threat is counted in the game summary. See the threat guide for how to train the habit before the cue appears.
Do I need an account?
No. Wins, unlocks, and a short game history stay in your browser. Clearing site data resets progress. Optional feedback can include an email only if you type one.
Next: how to spot the engine’s threat, meet the Stockfish bots, or choose an opponent.