File annotation symbol

A file is a vertical line of eight squares sharing one letter, from a through h. Rooks and queens can apply pressure along it. An open file contains no pawns, while a semi-open file lacks the pawn of one side.

The ⇔ and ⟺ signs indicate that a file deserves attention. Their horizontal appearance does not describe movement on the board; it is an editorial convention. The symbol also does not identify the file, say whether it is open, or name the side controlling it. The position or comment supplies that information.

Chess Informant labels this theme “file,” while Scid vs. PC calls proposed Numeric Annotation Glyph (NAG) $149 “line” and displays ⟺. $149 comes after the meanings assigned by the original Portable Game Notation (PGN) specification, the text format for storing games, so names and glyphs can vary across programs. Do not confuse it with the diagonal sign or the arrows for counterplay.