What the move labels mean
Every move is scored by what it costs against the engine’s best line, measured in centipawns — hundredths of a pawn. These are the thresholds this app applies.
- Bestunder 10 centipawns
A best move is one that loses almost nothing compared with the engine's preferred line — under 10 centipawns. It is usually the engine's first choice, but any move that close to it counts.
- Excellent10 to 49 centipawns
An excellent move loses between 10 and 49 centipawns against the engine's best line. It is not the top choice, but it gives up too little to change how the position should be played.
- Mistake100 to 199 centipawns
A mistake loses between 100 and 199 centipawns — a full pawn's worth of advantage or more, without quite throwing the game away. That is the threshold at which the assessment of the position genuinely changes.
- Blunder200 centipawns or more
A blunder loses 200 centipawns or more against the engine's best line — two pawns' worth of advantage. It is the grade at which the likely result of the game changes.
How accuracy is calculated
Accuracy is a single percentage over a whole game. Best and excellent moves cost nothing; an inaccuracy costs 25 penalty points, a mistake 60 and a blunder 100. The total is divided by the number of moves and subtracted from 100.
That means a short game is judged more harshly than a long one for the same number of errors, which is intended — two blunders in a twenty-move game is a different game from two in an eighty-move one.
Other sites weight accuracy differently, so the same game can score differently on each. None of them is wrong; they are answering slightly different questions. What matters is comparing your games against each other, using one scale.
Labels are not the whole story
A single game’s labels tell you what happened in that game, which you largely already know. What is harder to see — and what this app is built for — is whether the same grade keeps appearing in the same opening, as the same colour, or past the same move number.