FEN RegEx Goal of this RegEx is NOT to validate legal positions Board ([rnbqkpRNBQKP1-8]+\/){7}([rnbqkpRNBQKP1-8]+) Next Move [bw] Castling (-|KQ?k?q?|K?Qk?q?|K?Q?kq?|K?Q?k?q) En Passant (-|[a-h][36]) Halfmove Clock \d+ Fullmove Number \d+