Your mirror
The opponent plays your own opening book, loses material at the rate you lose it, and blunders at the frequency your games show — scaled up when the position is sharp, down when it is quiet.
Stockfish reader
Stockfish 19 reads every position in the background and grades each move — yours and the mirror’s — against what it would have played. Each position gets the time set here, answered within 5 ms of it and never after. The house engine stays the opponent; Stockfish is the check on it.
Game text
Copy this into the Review tab's PGN import to run a justification transcript on your own sparring game.
Read any public profile
Paste a Lichess profile link or username. The same measurement runs over the window chosen on the Strength tab and returns what that player should work on. Useful for preparing against an opponent, or for coaching someone else.
Training
Board
Data
Everything lives in this browser. The only outbound requests are to Lichess, and to an assistant API if you set a key below.
Written coaching (optional)
Without a key, the review still produces a full structured critique and hands you a prompt to paste elsewhere. A key entered here is stored in this browser only; treat it as you would any secret typed into a local page.
How the numbers are made
Measured strength blends three things: a FIDE-style performance rating over the window chosen at the top of the Strength tab (all time unless you narrow it), a strength estimate derived from average centipawn loss, and your listed rating as an anchor. The blend leans on results once there are enough of them and on move quality when there are not. The margin shown is the sampling error on the performance rating, so it narrows as you play. Motif labels are produced by geometric rules over the position rather than by a neural classifier: they are reliable for forks, pins, hanging pieces and back-rank patterns, and rougher for deflection and prophylaxis.