Extended Position Description

EPD stands for Extended Position Description. Its purpose is to represent a position and attach data that software can interpret, such as an expected answer, a record identifier, or a testing instruction.

The line begins with the same first four fields as FEN: piece placement, side to move, castling rights, and en passant target square. EPD does not require FEN's two trailing counters. It may instead contain zero or more operations.

How operations work

Each operation has a short code called an opcode, may contain one or more operands, and ends with a semicolon. The standard defines, among others, bm for moves considered best, am for moves to avoid, and id for a record identifier. This structure lets developers build test suites, opening libraries, and training sets without inventing a new syntax for every application.

EPD does not replace PGN when a complete game must be preserved. PGN organizes players, result, and a move sequence; EPD is designed around independent positions with attached attributes or commands.