Win by checkmating the opposing king. White moves first. Select one of your pieces, then a marked destination. In computer mode, choose White or Black using the side selector.
One space, four coordinates. Each square has an X file, a–d, and a Y rank, 1–4. The two board columns are Z = 0 and Z = 1. The two board rows are W = 1 at the top and W = 0 at the bottom. A square is written as a1 [0,0], with Z and W inside the brackets. Moving to the same square on an adjacent board changes just one axis.
Each side starts with a king, queen, two rooks, bishop, knight, and four pawns. The following movement rules apply equally to X, Y, Z, and W.
Move any distance along exactly one axis. It can travel within a board or to the same square on another board in the same row or column.
Move the same distance along exactly two axes. This includes ordinary diagonals and diagonals that cross between boards.
Move the same distance along any number of axes, from one to all four. Every changed coordinate must change by the same amount.
Move one step along any combination of axes. It may cross both Z and W in a single move, but may never enter an attacked square.
Jump two steps along one axis and one along a different axis. It jumps over pieces. On this board, the two-step part must use X or Y.
Move one empty square along Y. White goes toward rank 4, Black toward rank 1. Capture one Y step forward plus one step along exactly one of X, Z, or W. Reaching the last rank automatically promotes to a queen.
Blocking and check. All pieces except knights are blocked by pieces along their path. You cannot land on a friendly piece or leave your king in check. Checkmate ends the game; the king is never captured.
Pawns have no opening double move. There is no castling or en passant. Stalemate, a third repetition, 100 turns without a pawn move or capture, and two bare kings are draws. Each player's turn counts as one move in the journal.
Try a fourth-axis move. At the start, select White's rook on a1 in the bottom-left board. Move to a1 in the top-left board. X, Y, and Z stay the same; only W changes.
Keyboard. Tab to a square, then press Enter or Space to select a piece or move. Arrow keys move focus within a board. Alt + arrow keys move focus between boards. Escape clears your selection.