Evaluation

Evaluation summarizes the quality of a position under the assumption that both sides continue competently. It answers three questions: who is better, how large the difference is, and why. It is not the final game result, because an advantage still has to be turned into a win and an inferior position may still be defended.

Factors in a human evaluation

• Material: the amount and approximate value of the pieces and pawns.
• King safety: how easily the opponent can create checks or mating threats.
• Activity: the number and quality of useful squares available to the pieces.
• Pawn structure, meaning how the pawns are distributed and connected; available space, immediate threats, and lasting weaknesses.

A chess engine expresses evaluation as a number or as win, draw, and loss probabilities. Many interfaces show positive values for White and negative values for Black. A value near zero means balance according to the analysis, not a guaranteed draw. In Stockfish, for example, the modern scale is calibrated to winning probabilities and no longer represents a literal number of extra pawns.

Evaluation belongs to a specific position, including the final position of a calculated line. Comparing those evaluations helps identify the best move. A score can change when the engine examines more moves and discovers defenses or attacks it had not considered before.