application/vnd.chess-pgn

A media type is a label telling software what kind of data it is receiving. It is also called a MIME type, after Multipurpose Internet Mail Extensions, the convention's historical name. The Internet Assigned Numbers Authority (IANA), the authority that maintains technical Internet registries, records application/vnd.chess-pgn for games written in Portable Game Notation (PGN), a text format for recording chess games.

The label is not the content and does not prove that a file is valid. The data must still follow PGN rules. The IANA registration specifies no required or optional parameters, associates the .pgn extension, and states that there is no magic number, meaning no fixed opening byte signature that independently identifies the format.

application/x-chess-pgn is listed as a deprecated alias. Older software may still send it, but a new integration should emit the registered type. A receiver supporting legacy systems may reasonably accept both while treating the alias as compatibility only.