Game Rules

BigChess is a variant of chess played on a 10×10 board with additional pieces and modified rules. It preserves the strategic depth of traditional chess while introducing an expanded battlefield, a brand-new piece called the Clone, enhanced pawn movement, and adjusted castling mechanics. This document describes the complete rules of BigChess as implemented in the game.

The game is played on a 10×10 board containing 100 squares, alternating in light and dark colors just like a standard chessboard.

Algebraic Notation: The board uses algebraic notation where files (columns) run from A through I and M (ten files total), while ranks (rows) run from 1 to 10.

Starting Setup: Each player begins with the following pieces on their back rank and pawn rank:

• White's back rank (rank 1): Rook on a1, Knight on b1, Bishop on c1, Clone on d1, Queen on e1, King on f1, Clone on g1, Bishop on h1, Knight on i1, Rook on m1.
• White's pawns (rank 2): 10 pawns on a2 through i2 and m2.
• Black's back rank (rank 10): Rook on a10, Knight on b10, Bishop on c10, Clone on d10, Queen on e10, King on f10, Clone on g10, Bishop on h10, Knight on i10, Rook on m10.
• Black's pawns (rank 9): 10 pawns on a9 through i9 and m9.

Each side begins with 10 pawns instead of the standard 8 pawns in classical chess.

BigChess features an expanded set of chess pieces, each with their own unique movement patterns and strategic roles. There are seven piece types in total:

King: The King moves one square in any direction — horizontally, vertically, or diagonally. The King also has the ability to castle under specific conditions. The King is the most important piece: if it is checkmated, the game is lost.

Queen: The Queen is the most powerful piece on the board. She is capable of moving any number of squares diagonally, horizontally, or vertically, as long as no piece blocks her path. She combines the movement abilities of both the Rook and the Bishop.

Rook: The Rook moves any number of squares horizontally or vertically across the board, as long as no piece blocks its path. The Rook also participates in castling alongside the King.

Bishop: The Bishop moves any number of squares diagonally across the board. Each Bishop remains on the same color of square for the entire game. Since the board is 10×10, the diagonal dynamics offer new range and coverage compared to standard chess.

Knight: The Knight moves in a distinctive L-shape pattern: two squares horizontally or vertically, then one square perpendicular to that direction (or vice versa). The Knight is the only piece that can jump over other pieces.

Clone (New Piece): The Clone is a unique piece exclusive to BigChess. It combines the movement abilities of both a Knight and a Bishop. This means the Clone can either move in the L-shaped pattern of a Knight (and jump over pieces), or slide any number of squares diagonally like a Bishop. The Clone is a tremendously powerful piece that opens up entirely new strategic possibilities and tactical combinations. Each player starts the game with two Clones.

Pawn: The Pawn moves forward one square under normal circumstances. However, from its starting position, a pawn has the option to move forward 2 or 3 squares in a single move. Pawns capture diagonally, moving one square forward-left or forward-right to take an enemy piece. Pawns cannot move backward.

Standard Piece Movement:

• King: One square in any of the eight directions.
• Queen: Any number of squares in any of the eight directions (horizontal, vertical, diagonal).
• Rook: Any number of squares horizontally or vertically.
• Bishop: Any number of squares diagonally.
• Knight: L-shape (2+1 squares). Can jump over other pieces.
• Clone: Moves as either a Knight or a Bishop on any given turn.
• Pawn: One square forward (or 2–3 from starting position). Captures one square diagonally forward.

Pawn Movement:

• The pawn moves forward one square under normal circumstances.
• From its starting position (2nd rank for White, 9th rank for Black), a pawn can move forward 2 or 3 squares in a single move.
• Pawns capture enemy pieces by moving diagonally one square forward.
• Pawns can capture enemy pawns using the en passant rule under specific conditions.
• When a pawn reaches the opponent's back rank (10th rank for White, 1st rank for Black), it must be promoted to another piece.

En Passant: BigChess implements two variations of the en passant capture rule, adapted for the expanded pawn movement. Standard En Passant: If an opposing pawn makes a double-step or triple-step move and lands beside your pawn, you may capture it as if it had only moved one square forward. Your pawn moves diagonally to the square the enemy pawn passed through. Multi-Square En Passant: When an opposing pawn makes a triple-step move, your pawn may capture it over any of the squares that were passed during that triple move, not just the first one.

Pawn Promotion: A pawn must be promoted when it reaches the opponent's back rank (rank 10 for White, rank 1 for Black). The pawn is immediately replaced by a piece of the player's choice. Players can choose to promote their pawn to one of the following pieces: Queen, Rook, Clone, Knight, Bishop. Note that in BigChess, unlike standard chess, you can also promote a pawn to a Clone — the powerful Knight+Bishop hybrid.

Castling: Castling in BigChess is a special move involving the King and one of the Rooks. It is the only move where two pieces move simultaneously. The King moves three squares toward the Rook (instead of two squares as in standard chess). The Rook then jumps over the King and lands on the square immediately next to it on the other side.

Castling Conditions: Castling is only permitted when all of the following conditions are met:

• Neither the King nor the chosen Rook has previously moved during the game.
• All squares between the King and the Rook are empty — no pieces may stand in the way.
• The King is not currently in check.
• The King does not pass through or land on a square that is under attack by an enemy piece.

Castling Positions: White's King is on f1, with Rooks on a1 (queenside) and m1 (kingside). Black's King is on f10, with Rooks on a10 (queenside) and m10 (kingside).

Check: Check occurs when a King is under direct attack from an opponent's piece. The player whose King is in check must make a move that removes the check on their very next turn. This can be done by moving the King to a safe square, blocking the attacking piece with another piece, or capturing the attacking piece.

Checkmate: Checkmate happens when a King is in check and has no legal moves to escape the attack. The player who delivers checkmate wins the game.

Stalemate: Stalemate occurs when a player has no legal moves available but their King is not in check. The game ends in a draw.

Forfeit (Resignation): A forfeit happens when a player voluntarily resigns or abandons the game. The opposing player is awarded the victory.

Timeout: A timeout occurs when a player runs out of their allocated time. The player who runs out of time automatically loses the game.

Draw by Threefold Repetition: A draw by threefold repetition is declared when the same board position occurs three times during the game. The positions do not need to occur on consecutive moves — they can happen at any point throughout the game.

Draw by Insufficient Material: A draw by insufficient material occurs when neither player has enough pieces remaining on the board to achieve checkmate. For example, a King alone versus a King alone results in an automatic draw.

Draw by Force Majeure: A draw by force majeure is declared when the game must end due to external circumstances beyond the players' control (such as server issues or other technical interruptions).

A BigChess game can conclude through several different methods:

• Checkmate: The game ends in victory when one player achieves checkmate against the opponent's King.
• Stalemate: The game ends in a draw when stalemate is reached.
• Draw: The game can end in a draw through various circumstances such as agreement, threefold repetition, or insufficient material.
• Timeout: The game ends when a player exceeds their allocated time limit.
• Forfeit: The game ends when a player chooses to resign or abandons the match.

BigChess introduces several key differences compared to traditional 8×8 chess:

• Board size: 8×8 (64 squares) vs 10×10 (100 squares)
• Number of pawns per side: 8 pawns vs 10 pawns
• Piece types: 6 (King, Queen, Rook, Bishop, Knight, Pawn) vs 7 (adds the Clone — Knight+Bishop hybrid)
• Pawn initial move: 1 or 2 squares forward vs 1, 2, or 3 squares forward
• En passant: Standard (double-step only) vs Expanded (double-step and triple-step, multi-square targets)
• Castling distance: King moves 2 squares vs King moves 3 squares
• Pawn promotion options: Queen, Rook, Bishop, Knight vs Queen, Rook, Clone, Knight, Bishop
• File notation: a–h vs A–I and M
• Rank notation: 1–8 vs 1–10

Piece Summary Table:

Big Chess — Master the art of strategy on a 10×10 board with new Clone figures and advanced tactics that will challenge even the most experienced players.