Move Evaluation Symbols (i.e. Move Quality)

Chess Informant

Chess Informant is a periodical that started publishing chess games in 1966. It was the go-to source to find chess games played by master players. Chess Informant introduced many innovations to how chess games were classified (i.e. encyclopedia of chess openings), shared and enjoyed by others (often across language barriers).

One of those innovations is the following move evaluation symbols. These symbols were used to designate a move's quality based on the reviewer's (often a master player themself) assessment. (Source: https://en.wikipedia.org/wiki/Chess_annotation_symbols)

• "!!" - Brilliant move. These are very strong moves, usually difficult-to-find moves which require a high level of skill and calculation. Examples include sound sacrifices of large amounts of material and counter-intuitive moves that prove very powerful. For example, in what is known as the Game of the Century, annotators typically award a double exclamation point to 13-year-old Bobby Fischer's move 17...Be6, sacrificing the queen.
• "!" - Good move. These are moves that are surprising or require particular skill. The symbol may also be interpreted as "best move". Annotators are usually somewhat conservative with the use of this symbol. Reasons for awarding the symbol vary widely between annotators; among them are strong opening novelties, well-timed breakthroughs, sound sacrifices, moves that set traps in lost positions, moves that avoid such traps, and good psychological choices in the opening.
• "!?" - Interesting move. This is a controversial symbol. Different books and software have slightly varying definitions. Among the definitions are "interesting, but perhaps not the best move", "move deserving attention", "enterprising move" and "risky move". Usually it indicates that the move leads to exciting or wild play but that the objective evaluation of the move is unclear. It is also often used when a player sets a cunning trap in a lost position. Typical moves receiving a "!?" are those involving speculative sacrifices or dangerous attacks that might turn out to be unsound.
• "?!" - Dubious move. This symbol is similar to the "!?" but usually indicates that the annotator believes the move to be dubious or questionable but to possibly have merits. The "?!" may also indicate that the annotator believes the move is weak/deserving of criticism but not bad enough to warrant a "?". A sacrifice leading to a dangerous attack that the opponent should be able to defend against if they play well may receive a "?!". Alternatively, this may denote a move that is objectively bad but sets up an attractive trap.
• "?" - Mistake. This move is a mistake and that it should not have been played. Mistakes often lead to loss of tempo, material, or otherwise a worsening of the player's position. The nature of a mistake may be more strategic than tactical; in some cases, the move receiving a question mark may be one for which it is difficult to find a refutation. A move that overlooks a forthcoming brilliant combination from the opponent would rarely receive more than one question mark, for example.
• "??" - Blunder. This is a very bad move that severely worsens the player's position. Typical moves that receive double question marks are those that overlook a tactic that wins substantial material or overlook a checkmate. A "??"-worthy move usually results in an immediately lost position. Occasionally, the sign is used for a move that transforms a won position into a draw. Though more common among less experienced players, blunders occur at all levels of play.

Lichess.org

Source: https://github.com/lichess-org/lila/blob/master/modules/analyse/src/main/Advice.scala

• Inaccuracy
• Mistake
• Blunder

Chess.com

Source: https://support.chess.com/article/2965-how-are-moves-classified-what-is-a-blunder-or-brilliant-and-etc

• Brilliant (!!)
• Excellent (!)
• Best
• Good
• Book
• Inaccuracy (?!)
• Mistake (?)
• Miss (X)
• Blunder (??)

To-do

• Add some background on how lichess.org and/or chess.com calculate the above