Chesskers is chess with extended rules. The pieces move as they do in chess, and checkmate wins the game. But pieces can also capture checkers-style: they jump enemy pieces, and keep jumping in a chain. And a knight sweeps up every enemy piece on its way.
Replacement captures
Every piece captures as in chess: it moves onto an enemy piece's square, and the enemy piece leaves the board. This is a replacement capture.
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Jump captures
A rook, bishop, queen, king or pawn can also make a jump capture: it passes over an enemy piece along one of its lines of movement, and lands on the empty square just beyond it, its landing square. The jumped piece leaves the board.
- A rook, bishop or queen may come from any distance along a clear line. It jumps only the first piece on the line, and lands just beyond it, going no further.
- A king jumps an enemy piece next to it, in any direction. A pawn jumps one diagonally forward only.
- Your own pieces block your jumps, and a jump needs its landing square empty.
- A knight never jumps.
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Chains
After a jump capture, the same piece may jump again from its landing square, and again after that: a chain, all in one turn.
- Each jump after the first is over an enemy piece right next to the piece, with an empty square beyond it: a piece, a space, a piece, a space.
- The direction can change from one jump to the next, along the piece's own lines: a rook turns corners, a bishop zig-zags, and a chain may even turn back the way it came.
- Each jumped piece leaves the board as it is jumped.
- A chain is made only of jump captures, and you may stop it after any jump. A pawn that lands on the last rank promotes, and its chain ends there.
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To make a chain, tap the piece, then each landing square in turn. The move ends by itself once no jump is left. To stop early, tap the piece again; to undo a jump, tap the square it last jumped from.
Sweep captures
A knight has a capture of its own. Each of its moves has a leg: the two squares it passes straight over, along the long side of its L, before its step to the side.
- A knight that lands on an empty square captures every enemy piece on the leg of that move: a sweep capture. It isn't a choice.
- Its own pieces on the leg stay where they are, and don't block it.
- A knight that lands on an enemy piece captures that piece only, by replacement.
b * . . . . . . 3 p . . . . . . . 2 N . . . . . . . 1 a b c d e f g h
Check
A king is in check when the opponent could capture it with their next move, by any kind of capture: by replacement, by a sweep capture, or by a jump at any point in any chain. You may never leave your own king in check, and that is judged on the position after your whole move: in a chain, a king may pass over squares under attack, as long as it ends the move safe.
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Checkmate wins, as in chess. But a king can escape check by a jump, too, so some of chess's mates are not mate here.
The knight mate
In chess, a king and a knight can't checkmate a lone king. In Chesskers they can.
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The rest is chess
- Castling is as in chess, but the king's square, the square it passes over and the square it lands on must each be safe from every kind of capture.
- En passant is as in chess: a replacement capture only, never a jump or part of a chain.
- Promotion: a pawn that reaches the last rank, by a step, a replacement capture or a jump, becomes a queen, rook, bishop or knight, whichever you choose.
- Draws: stalemate, threefold repetition and the 50-move rule, where every kind of capture starts the count again. The game is drawn for insufficient material only when two kings are left, or two kings and a bishop: a king and a knight can mate, so they play on. In an Online game you may also offer a draw: it stands until your opponent accepts or declines it, or moves instead.
- You may resign at any time. In Pass-and-play and Bot games, moves can be taken back: in a Bot game, back to your last turn.
- In an Online game, a player who leaves the table mid-game has 10 minutes to come back, counted while their opponent waits there. If they don't, they forfeit, and their opponent wins.
The move list
Moves are written in chess notation, extended for the variant:
Rxa5is a replacement capture,Ra1:a6:a8a chain: its start square, then each landing square,N~b3a sweep capture, with the pieces it captured shown beside it,- and
+marks check,#checkmate.
The pieces are Colin M.L. Burnett's, used under the 3-clause BSD licence: its notice.