The Chess Room

Sit down across from Stockfish, the strongest chess engine in the world, at the rank you choose. A game is already set: you command White against the Tactician. Drag or click to move. Every move on the table, yours and the engine’s, is read the moment it is played: its grade, every tactic it achieved, what it allowed, what was better, and the principle of war behind it.

Opponent’s rank

Your colors

Connecting to Stockfish…

The DebriefEvery move, read and graded

The verdict

Stockfish scores the position before and after every move and converts the score into winning chances. The grade is how much of those chances the move gave away, using the Lichess thresholds.

!! Brilliant	The best move, and a sound sacrifice of material.
! Great	The only move: every alternative gives away at least 10 points of winning chances.
★ Best	The engine's first choice, or equal to it.
✓ Good	Gives away less than 5 points.
!? Interesting	A speculative sacrifice that is not refuted outright.
?! Dubious	Gives away 5 to 10 points.
? Mistake	Gives away 10 to 15 points, or misses a forced mate.
?? Blunder	Gives away 15 points or more.

Tactics the analysis names

Fork	One piece attacks two targets at once (knight fork, pawn fork, royal fork on king and queen). Sun Tzu VII: divide the opposing force.
Pin / Skewer	A piece cannot move without exposing what stands behind it; a skewer puts the more valuable piece in front. Sun Tzu III and VIII.
Discovered check / attack	Moving one piece opens a line for another. Double check: both give check. Sun Tzu X.
Removes the defender	Captures the piece that was guarding another target.
Overload	One defender is the only guard of two targets.
Trap	A piece is attacked and has no safe square.
Threatens mate / Stops a mate threat	Mate next move if not answered, or the answer that prevents it.
Sacrifice	Material offered for something greater. Sun Tzu X.
Zugzwang	The side to move would be better off passing; every move worsens its position. Sun Tzu IX.
Also named	Checks, checkmate, stalemate, winning material, trades, promotion, passed pawns, open files, doubled rooks, castling, development, the center, saving an attacked piece.

The ten principles a suggested move can fulfill

While Arrows is on and it is your move, a teal arrow points to the legal move that fulfills the most of these — never the engine's own favorite move, only the one doctrine favors. The panel under the board names which ones it fulfills.

1 · Center Control	Occupies d4, d5, e4, or e5 with a pawn or knight.
2 · Development	Brings a new minor piece off the back rank in the opening.
3 · Material	Wins material outright, or any resulting trade favors you.
4 · King Safety	Castles the king to safety.
5 · Initiative / Tempo	Checks, mates, or creates a new threat the opponent must answer.
6 · The Unspent Threat	Holds an existing pin or skewer rather than cashing it in before it's necessary.
7 · Coordination	Lands where it now supports another friendly piece.
8 · Opportunity Creation	Forks, pins, skewers, a discovered attack, an overload, a trap, zugzwang, or a sound sacrifice.
9 · Pawn Structure	Creates or advances a passed pawn, or seizes an open or half-open file.
10 · Opposition	In a king-and-pawn ending, takes or holds the opposition.

Engine: Stockfish 19 via Stockfish.js (© Chess.com, LLC; the Stockfish developers), GNU GPL v3 — source: github.com/nmrugg/stockfish.js, github.com/official-stockfish/Stockfish. If Stockfish cannot load, a built-in backup engine plays and grades instead. Chess pieces: Colin M.L. Burnett, Wikimedia Commons, CC BY-SA 3.0. Levels 2–5 use Stockfish's own strength calibration; Recruit uses its lowest skill setting.