• Each player starts with 5 pieces lined up on their own edge of a 5x5-point board.
• Move one piece per turn, one step along a line.
• Trap an enemy piece between two of yours in a straight line to capture it.
• Win by reducing your opponent to one piece, or leaving them with no legal move.
• If 40 moves in a row (both sides counted) pass with no capture, the game is a draw.

Korean Gonu's "line" variants are named by their grid size — 넉줄고누 (4-line), 다섯줄고누 (5-line, this one), 여섯줄고누 (6-line), and so on — all playing by the same rules, just with more room on a bigger board.