Repertoire statistics

Chessbook tries to grade repertoires on a few different things, because "is this repertoire good?" is not really one question.

The main stats are:

• Effectiveness: how well the positions in your repertoire tend to score in real games at your level.
• Soundness: how little engine evaluation your repertoire gives away, along the paths opponents actually take against it.
• Learnability: how easy your repertoire should be to remember.

These are separate on purpose. A repertoire can score well in practice while being a bit unsound, or be completely sound but full of rare, fiddly lines that are hard to remember.

How the scores are scaled

Each of the three stats is a score from 1 to 99, and the app also shows the sum of the three as a single overall number.

The scale is anchored at both ends:

• A score of 1 represents a bad but plausible repertoire for your rating, side, and coverage goal — not a deliberately self-destructive one. For effectiveness, that anchor comes from the bottom 10% of real online repertoires; for learnability, from the bottom 10% of repertoires assembled from real book moves in proportion to how often people actually play them; for soundness, from a severe gambit-scale concession.
• A score of 99 represents the best repertoire Chessbook's auto-fill can construct when it focuses entirely on that one stat, for your rating, side, and coverage goal. The last couple of points are treated as a small saturation band, so equally-good builds near the top all show 99.

So the scores describe where you sit on a useful, achievable range — they are not percentiles against other users. A 50 doesn't mean half of players have a better repertoire than you; it means you're halfway between a bad-but-plausible repertoire and the best build we know how to make.

One consequence worth knowing: changing your coverage goal can change the scores. Preparing more opponent responses adds useful coverage, but it can also require harder-to-remember lines or expose tradeoffs that didn't appear in a smaller repertoire.

There are also progress stats like completion and Mastery, which are more about how much of the repertoire you've built and learned.