ChessGrader / Guides / Move classifications
Chess move classifications, explained
Every graded chess move falls into one of ten classes, from Brilliant down to Blunder. Here's what each label means, the exact win-probability thresholds behind them, and why the same move can get different labels on different sites.
These are the definitions ChessGrader uses — and unlike most sites, the thresholds are fully published. The quick version: an inaccuracy loses at least 10% win probability, a mistake at least 20%, and a blunder at least 30%.
All ten grades at a glance
| Grade | Symbol | Meaning | Threshold |
|---|---|---|---|
| Brilliant | !! | Best move that's also a genuine, sound sacrifice | Engine's best + static exchange < 0, not already winning, verified at depth |
| Great | ! | The only good move, or the precise punish of a game-turning error | Second-best line ≥18% worse in win probability, verified at depth |
| Best | ★ | The engine's top choice | Matches line 1, or ties line 2 within 10cp |
| Excellent | — | Nearly as good as the best move | ≤25cp loss |
| Good | — | Fine move, small cost | More than 25cp, but under 10% win-probability drop |
| Book | — | Known opening theory | Theory-range move in the first 8 moves |
| Inaccuracy | ?! | Noticeably worse than the best move | ≥10% win probability lost |
| Miss | ✗ | Opponent handed you the game and you gave it back | Failed to convert a gifted advantage, incl. missed forced mates while winning |
| Mistake | ? | A move that seriously damages your position | ≥20% win probability lost |
| Blunder | ?? | A move that throws away the game or a decisive advantage | ≥30% win probability lost |
Each grade in a bit more detail
Brilliant (!!)
The engine's best move that is also a genuine sacrifice — material given up by the raw capture arithmetic, in a position you hadn't already won, and still sound afterwards. It's the rarest label by design; many games have none. Full breakdown on the brilliant moves page.
Great (!)
A move that had to be found. Either it was the only good move — the second-best option at least 18% worse in win probability — or it was the precise move that punished an opponent error which had turned a lost or equal game. Like Brilliant, it can only be awarded after deep verification.
Best (★)
You played the engine's top choice, or a move that ties its second line within 10 centipawns — at that margin the engine itself can't reliably tell them apart, so you get full credit. Strong players collect a lot of these.
Excellent
Not the engine's first choice, but within 25 centipawns of it. In practice the difference between Best and Excellent rarely matters over the board.
Good
A reasonable move that gave up more than a sliver, but stayed under a 10% win-probability drop. Your position is a bit worse than it needed to be, and that's all.
Book
A move in known opening theory, within the first 8 moves and with low loss. Book moves are excluded from your mistake counts — you're reciting, not calculating.
Inaccuracy (?!)
You lost at least 10% win probability. One inaccuracy is background noise; a string of them is how equal positions quietly become lost ones.
Miss (✗)
The label most sites don't have. Your opponent handed you the game — a blunder that gave you a decisive advantage — and your reply gave it straight back. It includes missing a forced mate while still winning. A Miss often loses little evaluation on paper; what it cost you is the win that was sitting there.
Mistake (?)
At least 20% win probability lost. A mistake changes the character of the game — an edge becomes equality, equality becomes trouble.
Blunder (??)
At least 30% win probability lost. This is the game-changer: a winning position becomes equal, or an equal one becomes lost. Reducing blunders is the fastest rating gain available at every level below master.
How forced mates are handled
Mates break centipawn math — "mate in 3" isn't a number you can subtract from. Most tools handle this crudely. ChessGrader uses three explicit rules:
- A longer route to a forced mate is never punished. If you had mate in 2 and played a move that gives mate in 5, you're still mating. The grade floor is Excellent.
- Losing a forced mate while still winning is a Miss, not a blunder. The naive math would score a vanished mate as a maximum-loss catastrophe even if you're still up a rook. You missed the kill; you didn't throw the game.
- A defender already facing forced mate isn't charged extra. When every move loses, no move is a blunder. You don't get punished for the inevitable.
Why thresholds use win probability, not centipawns
A 100-centipawn loss in an equal position turns a draw into a loss; the same 100 centipawns at +9.00 changes nothing. Raw centipawn thresholds would call both the same. So each evaluation is converted to a win percentage first — via the logistic curve documented on the methodology page — and grades are defined by how much win probability a move gave up. That's why a "small" eval drop in a sharp position can be a blunder while a big eval drop in a won position isn't.
Are labels the same everywhere?
No. Chess.com, Lichess, and ChessGrader all grade with Stockfish, but the label sets and thresholds differ. Lichess only marks Inaccuracy, Mistake, and Blunder. Chess.com uses a similar ten-ish label set to ChessGrader's but with proprietary thresholds. ChessGrader's grades typically land within one step of chess.com's on the same game — and every rule above is published, so disagreements can be checked rather than argued about. To see them applied to your own games, run a free game review.
Frequently asked questions
What's worse, a mistake or a blunder?
A blunder is worse. A mistake loses at least 20% win probability, while a blunder loses at least 30% — typically enough to flip the result of the game, like turning a winning position into an equal one or an equal position into a lost one.
What is a Miss in chess analysis?
A Miss means your opponent blundered and handed you a decisive advantage, and your very next move gave it back — including failing to play a forced mate while still winning. It is graded separately from mistakes and blunders because the evaluation loss on paper can be small even though a win slipped away.
Why was my move called an inaccuracy when it won material?
Because grading compares your move to the best move available, not to doing nothing. If capturing a pawn cost you 10% or more win probability compared to a stronger option — say, a mating attack or winning a whole piece — it is an inaccuracy even though it gained material.
Are move labels the same on every chess site?
No. Lichess only labels Inaccuracy, Mistake, and Blunder. Chess.com uses a fuller label set with proprietary thresholds. ChessGrader uses ten grades with fully published win-probability thresholds. The same move can receive different labels on different sites, usually within one step of each other.
What win probability loss makes a move a blunder?
In ChessGrader, a blunder is a move that loses at least 30% win probability, a mistake at least 20%, and an inaccuracy at least 10%. Thresholds are set in win probability rather than centipawns so that the same evaluation drop counts more in balanced positions than in already-decided ones.
Is taking longer to checkmate counted as a mistake?
Not in ChessGrader. A longer route to a forced mate is never punished — if you had mate in 2 and chose a line that mates in 5, the move is graded at least Excellent, because you are still winning by force.
What is a Book move?
A Book move is a move from known opening theory, played within the first 8 moves with low evaluation loss. Book moves are labeled separately because you are following established lines rather than calculating, and they are not counted against your accuracy in a meaningful way.