Best move

The best move is the option that preserves or improves a player's prospects as much as possible when the opponent answers in the strongest way. In a solved position, whose perfect result is known with certainty, it can be identified without doubt. In most positions it is estimated through human analysis or the search of a chess engine, a program that examines moves and positions.

“Best” does not necessarily mean spectacular, aggressive, or difficult. It may be a quiet defense, a simple exchange of pieces, or the only move that avoids losing. Two or more moves can also produce practically equal results. An interface may rank one first even when the difference has no practical significance.

An engine chooses according to its evaluation, meaning its judgment of which side stands better, and according to how far it has searched and how it is configured. The sequence it currently considers optimal is its principal variation, but that sequence can change with more analysis. A human calculation tree follows the same basic aim: compare alternatives against the strongest replies found. An automatic “best” label is therefore strong evidence, not absolute certainty when the position has not been solved completely.