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#

Also known as: checkmate sign

The # sign is appended to a move that gives checkmate and ends the game.

Explanation

The # sign at the end of a move means that the opposing king is under attack and no legal reply can remove that attack. This position is checkmate, so the game ends immediately.

In the standard form of , called Standard Algebraic Notation (SAN), Qxf7# reads as: the queen captures on f7 and gives mate. Q represents the queen, x describes the capture, and # describes the effect on the king. The mate sign comes at the end of the move.

Portable Game Notation (PGN), the plain-text format for game files, uses # as its standard form. On a tournament scoresheet governed by the International Chess Federation (FIDE), ++ is also accepted for mate and both marks are optional. PGN does not reserve ++ for double check: a check that is not mate uses , while mate uses #.

Usage and context

In a complete PGN file, the result is also recorded separately as when White wins or when Black wins. # describes the mating move but does not replace the result marker.

Common confusions

# and +

# means that no legal defense exists and the game has ended. + means the king is in check but at least one legal reply remains.

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Sources

  1. 1.FIDE Laws of Chess taking effect from 1 January 2023, FIDE
  2. 2.Standard: Portable Game Notation Specification and Implementation Guide, rec.games.chess contributors, coordinated by Steven J. Edwards

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