Effectiveness

This repertoire statistic estimates how well your repertoire scores in real games at your level. A win counts as one point and a draw as half a point.

Chessbook follows your prepared lines and looks at the expected result of the positions you reach, using games from players in your rating range. Those positions are then weighted by how often opponents actually reach them against your repertoire, so you get rewarded more for high-scoring positions that are also likely to happen. Having a bunch of high-winrate traps that almost never occur won't move the score much.

When a line has very little data, we use a conservative estimate rather than taking the raw win rate at face value. A rare trap that scored well in a handful of games can't look unbeatable just because nobody has played the refutation yet.

The raw expected score is then converted to a 1–99 score. The bottom of the scale is anchored to the weakest real repertoires people actually play, and the top to the most effective repertoire Chessbook's auto-fill can construct — both for your rating, side, and coverage goal. See how the scores are scaled for details.

A high score means the repertoire tends to produce good practical results for players at your level. It doesn't necessarily mean every move is the engine's first choice — that's what Soundness measures, and the two often disagree in interesting ways.