The board

Play moves directly on the board to explore variations — every move you try becomes a branch in the move tree, and you can jump back to the actual game at any point. Use Import to paste a PGN from Chess.com, Lichess or any other source, and the whole game loads instantly. Right-click and drag to draw your own arrows and marks on the board.

Evaluation bar

The evaluation bar tracks the engine's verdict for the position you are currently viewing. A value like +1.5 means White is ahead by roughly one and a half pawns; negative values favor Black, and a mate score announces a forced checkmate in the given number of moves. The bar updates live while the engine calculates.

Move classifications

After running the analysis, every move receives a quality label. Flawless is the engine's optimal move; Polished and Solid are strong, safe alternatives; Theory marks moves known from opening theory. Inaccuracy, Mistake and Blunder mark increasing amounts of thrown-away advantage, and Marvelous highlights brilliant tactical moves, typically involving a sacrifice. The system is intentionally strict: moves are measured by how much win probability they give up compared to the engine's top choice, so scores tend to be lower — and more honest — than on more lenient platforms.

Accuracy, Performance and the evaluation plot

The stats panel summarizes the finished analysis: an Accuracy percentage for both players, an estimated Performance rating for this single game, a count of every move classification, and an evaluation plot that charts the engine score move by move. Click any point of the plot — or any classification — to jump straight to that moment in the game.

Computer panel and live analysis

The Computer tab runs Stockfish live on the position you are viewing and lists its preferred continuations with their evaluations, next to the game's move list. Start analysis evaluates the entire game move by move and fills the stats panel. On smaller screens the side panels merge into one tabbed panel below the board, so every tool remains reachable.

Engine settings: profiles and parameters

The settings dialog lets you pick an engine build — from the lightweight Stockfish 10 to Stockfish 18 with its full neural network — and tune how it thinks: threads (CPU cores), hash memory and search depth. Higher values give more stable evaluations but take longer. The engine runs locally in your browser, so speed and evaluations can vary with your hardware; the defaults are a good balance for most machines.