Accuracy
Accuracy is a percentage produced by analysis software that summarizes how closely a player's moves matched the engine's preferred choices over a game, with higher numbers meaning fewer costly errors.
Also called: accuracy score
An accuracy score condenses a whole game into one number. The software compares each move you played with what the engine would have chosen and weighs how much each deviation changed the evaluation. Different tools compute it differently, so a figure from one program cannot be compared directly with a figure from another. A club player meets accuracy right after a game and often reads too much into it. A high score can come from a quiet game in which nothing much happened, or from playing along a forced line where there were few real choices. A low score may come from one terrible move in an otherwise sensible game. The common mistake is chasing the percentage itself, for example by choosing engine-like moves you do not understand. A better habit is to use accuracy only as a pointer: if it is low, find the two or three moments where the evaluation swung and study those. The number says where to look, while the explanation of why you erred still has to come from your own review.
It sits close to Average centipawn loss. Average centipawn loss, or ACPL, is the mean amount of evaluation a player gave up per move compared with the engine's best choice, measured in hundredths of a pawn, so lower figures mean cleaner play.
It sits close to Centipawn. A centipawn is one hundredth of a pawn, the small unit engines use to report evaluations, so a score of 150 centipawns means the engine thinks one side is about one and a half pawns better.
A neighboring idea is Inaccuracy. An inaccuracy is the mildest error label in game review, given to a move that is playable but gives up a small amount of advantage compared with the engine's better alternative.
An engine can tell you what "Accuracy" means for a position, but not which mistakes you keep making; a first lesson with George Li reviews your games and finds those.
Related terms
Average centipawn loss, or ACPL, is the mean amount of evaluation a player gave up per move compared with the engine's best choice, measured in hundredths of a pawn, so lower figures mean cleaner play.
A game review is an automatic engine pass over a finished game that marks each move, shows how the evaluation changed and points out the turning points, mistakes and missed chances.
The best move is the move an engine rates highest in a given position after searching, usually shown first in its list of candidate lines and marked with the strongest evaluation.
A blunder is a very serious error, such as leaving a piece undefended or missing a decisive tactic, that swings the evaluation so far that a good position turns bad or a bad one becomes lost.
An evaluation is a numerical judgment of who stands better in a position, usually given in pawns from White’s point of view, where positive favors White and negative favors Black.
Post-game analysis is the discussion or private review held right after a game, in which both players or one player alone retrace the moves and identify the turning points, missed ideas and lessons.
Guides that go further
What to decide first, the questions to ask, what a first lesson should show and the red flags to avoid.
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A game review, a read on your level and a written study plan from George Li.
Want to spot this in your own games?
A first lesson starts with your games: George reviews them and builds a study plan around what he finds.