How we measure which openings punish mistakes
Every opening in the trainer carries one number per rating band: of the opponents who reach it, the share who make a mistake on the lines we teach. This page is the whole method, with the exact figures the current build uses. Nothing here is typed by hand; it is read from the same index the app ranks with, and a test fails the build if the two ever disagree.
What a finished claim looks like
- Vienna Gambit: 62% of Lichess players rated 1600–1799 who reach the Vienna Gambit make a mistake or blunder on the lines we teach within the first 10 moves (1.9M games, a lower bound).
- Evans Gambit: 3% of Lichess players rated 1600–1799 who reach the Evans Gambit make a mistake or blunder on the lines we teach within the first 10 moves (1.5M games, a lower bound).
- Danish Gambit: 22% of Lichess players rated 1600–1799 who reach the Danish Gambit make a mistake or blunder on the lines we teach within the first 10 moves (5.1M games, a lower bound).
1. Where the games come from
The Lichess opening explorer, blitz, rapid, classical games, split into seven rating bands (<1200 · 1200s · 1400s · 1600s · 1800s · 2000s · 2200+) plus an all-levels total. We use per-move aggregates only: how many games in a band reached a position and what was played there. A band prints a number only when at least 1.0K games in that band reached the opening's root position.
2. How a move is graded
Each popular reply is evaluated with Stockfish at depth 20 and compared with the engine's best move in the same position, in win-probability points, from the mover's point of view. The label comes from the classifier the game review uses (classifyMove): a drop above 5.75 points is a Mistake, above 19.25 a Blunder. Only Mistake (?) and Blunder (??) count. Inaccuracies are deliberately left out: that band is narrower than engine noise between depths.
3. How it adds up
Every opening has a declared root: the position after which it is on the board, with the opponent to move. From there we walk the taught lines as a tree. At each position the share of games that played a counted mistake is added, weighted by the share of games that followed our line to that position. Where the opponent has several taught replies their branches add, because they are different games. Where we have two answers to the same reply, only one branch is followed, the one a learner would study, so the total can never double-count. Games that leave our lines with a good move drop out and never return: the figure is a lower bound, and each row also records how much of the reached traffic it graded. The bars next to each opening show the slip rate move by move among opponents still on the line; the horizon is the mined depth, 11 moves.
4. What we verify at depth 30
Depth-20 evaluations move by a few win-probability points between depths, so a reply graded 6.15 points is not a reliable Mistake. Any counted reply that moves an opening's headline by at least 0.5 of a point and sits within 3 points of a bar is re-graded from full depth-30 searches of both positions, and the deeper verdict is final.
313 headline-moving replies across 70 openings · 93 close calls · 91 verified at depth 30 — 2 pending; their openings are marked until the pass completes.
5. What we do not claim
- The mistake rate is not a win rate, and not a measure of how good an opening is: it measures the share of opponents who reach the opening and then slip early against these lines. The win rate, the well-prepared lift and the win chance after move 11 are separate figures, defined in section 6.
- Not a share of players: a share of games in a band that reached the position.
- Not exact: a lower bound, because ungraded and rare replies never count.
- Not the whole game: the horizon is the first 11 moves of the taught lines.
6. Win rate, well-prepared lift and win chance after move 11
Three more figures sit next to the mistake rate, each per opening and per rating band, each from the owning side’s point of view. They come from the Lichess open database (CC0 monthly dumps), May and June 2026: every rated blitz, rapid and classical game between two human players, banded by the average of both ratings, exactly as the Lichess opening explorer buckets a game. No usernames or game ids are kept; only counts.
- Win rate: wins over every game that reached the opening’s root position, by whatever move order. Printed from 1.0K games in a band.
- Well prepared: among the games that carry Lichess server evaluations, the win rate of players who were never the first to leave established theory, and no mistake or blunder before move 11 (a mistake is a loss of more than 5.75 win-probability points on one move, a blunder more than 20), minus the win rate of every evaluated game in the band. Printed as a difference in points, from 300 well-prepared games among 1.0K evaluated ones. Well-prepared players also tend to be slightly stronger players, so read the lift as what preparation went with, never as what it caused.
- Win chance after move 11: the owning side’s mean win probability at that point over the evaluated games, a game that ended earlier counting at its result. Printed from 1.0K evaluated games.
Index built 2026-09-24. Data: Lichess.
Frequently asked questions
Of the Lichess games in that rating band that reached the opening's root position, at least 22% saw the opponent play a move our engine grading labels a Mistake (?) or Blunder (??) somewhere on the lines we teach, within the first 11 moves. It is a share of games that reached the position, never a share of all players, and it is a lower bound.
Only moves we have listed and graded can count. A rare reply that never made the table, or a popular one the engine pass has not graded yet, contributes nothing — even if it is a mistake. We publish how much of the reached traffic each figure has actually seen (the coverage), and hide the number when that falls under 80%.
The mistake rate measures one thing: the share of opponents at a given level who reach an opening and then go wrong early against its taught lines, graded move by move against the engine. The win rate is the plain outcome: of every Lichess blitz, rapid and classical game in the band that reached the opening, the share the owning side won. One tells you where preparation pays; the other tells you who wins in the end. Both are printed, and they are never the same number.
Among the games in that band that carry Lichess server evaluations, we take the players who were well prepared — never the first to leave established theory, and no mistake or blunder before move 11 — and compare their win rate with the win rate of every evaluated game in the same band. "+9 pts" means they won nine percentage points more often. It is printed as a difference on purpose: only about six percent of games carry evaluations and the players who request them are not a random sample, so their win rate is never shown next to the everybody-else rate as if the two were comparable. The difference is measured inside one set of games, where that tilt cancels.
The owning side's average win probability at the end of move 11, converted from the engine evaluation the way Lichess converts it, over the evaluated games in the band. A game that ended before move 11 counts at its result. It is the size of the advantage the opening produced, before the middlegame decides what becomes of it.
The reply data was last mined on 2026-10-03 and the index rebuilt on 2026-10-13. A freshness check in our build warns when the mine is older than four months.
The numbers live on every opening guide and inside the trainer, ranked for your own rating band.
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