Complete FIDE Chess Rules Reference¶

This reference document serves as the authoritative rules baseline for ChessWithQuests, ensuring our engine, validator (MoveValidator), board model (Board), and game manager (GameManager) faithfully adhere to standard international chess rules.

1. Board & Initial Setup¶

The game is played on an $8 \times 8$ grid of 64 alternating light and dark squares.
Ranks: Rows numbered 1 through 8 (Rank 1 is the White back rank; Rank 8 is the Black back rank).
Files: Columns lettered a through h (from White's left to right).
Orientation: The board is placed so that each player has a light square on their bottom-right corner (h1 for White, a8 for Black).
Initial Placement:
White pieces occupy Rank 1 (Rook on a1/h1, Knight on b1/g1, Bishop on c1/f1, Queen on d1, King on e1) and Rank 2 (Pawns on a2–h2).
Black pieces occupy Rank 8 (Rook on a8/h8, Knight on b8/g8, Bishop on c8/f8, Queen on d8, King on e8) and Rank 7 (Pawns on a7–h7).
"Queen on her color": White Queen begins on light square d1; Black Queen begins on dark square d8.

2. Standard Piece Movements¶

King (K)¶

Moves exactly 1 square in any direction: horizontally, vertically, or diagonally.
May never move into a square attacked by an enemy piece (moving into check is strictly illegal).
May not be placed adjacent to the opposing King.

Queen (Q)¶

Moves any number of vacant squares along ranks, files, or diagonals (combines the movement vectors of the Rook and Bishop).
Cannot leap over intervening pieces.

Rook (R)¶

Moves any number of vacant squares horizontally or vertically along ranks or files.
Cannot leap over intervening pieces.

Bishop (B)¶

Moves any number of vacant squares along diagonals.
Each Bishop remains confined throughout the game to squares of its initial color (one light-squared Bishop, one dark-squared Bishop per side).
Cannot leap over intervening pieces.

Knight (N / Horse)¶

Moves in an L-shape: 2 squares along a rank/file and 1 square perpendicularly, or 1 square along a rank/file and 2 squares perpendicularly (8 potential target coordinates).
Jumping capability: The Knight is the only piece permitted to leap over intervening pieces on its path.

Pawn (P)¶

Normal Advance: Moves 1 square straight forward along its file if the target square is unoccupied.
Initial Two-Square Advance: From its starting rank (Rank 2 for White, Rank 7 for Black), a pawn may optionally advance 2 squares forward, provided both intermediate and destination squares are vacant.
Capture: Captures 1 square diagonally forward (left or right). A pawn cannot capture directly forward.

3. Special Moves¶

Castling (O-O and O-O-O)¶

A simultaneous movement of the King and a Rook of the same color along the player's first rank: - Kingside (Short) Castling O-O: King moves from e1 to g1 (e8 to g8), and the h-rook moves to f1 (f8). - Queenside (Long) Castling O-O-O: King moves from e1 to c1 (e8 to c8), and the a-rook moves to d1 (d8). - Mandatory Requirements: 1. Neither the King nor the chosen Rook has moved earlier in the game. 2. All squares between the King and the Rook must be empty. 3. The King is not currently in check. 4. The square the King passes across is not attacked by an enemy piece. 5. The square the King lands upon is not attacked by an enemy piece.

En Passant¶

When a pawn advances 2 squares from its starting position and lands directly adjacent horizontally to an enemy pawn on that pawn's 5th rank (for White) or 4th rank (for Black).
The enemy pawn may capture this advanced pawn "in passing" by moving diagonally forward into the square the advanced pawn just skipped over.
Immediate Requirement: En passant must be claimed immediately on the turn following the two-square advance. If not played on that turn, the right to capture en passant on that pawn is permanently lost.

Pawn Promotion¶

When a pawn reaches the eighth rank (Rank 8 for White, Rank 1 for Black), it is immediately converted to a Queen, Rook, Bishop, or Knight of the same color as chosen by the player.
Promotion takes effect instantly and is not constrained by whether pieces of that type were previously captured (e.g. multiple Queens are permitted).

4. Check, Discovered Check & Checkmate¶

Check¶

A King is in check when it is under direct attack by at least one opposing piece.
A player whose King is in check must eliminate the check on that turn. A check can be resolved by:
Moving the King to an unattacked square.
Capturing the checking piece.
Blocking (interposing) a friendly piece along the line of attack between the checking piece and the King (blocking is not possible against Knight checks or double checks).

Discovered Check & Double Check¶

Discovered Check: Moving a piece unmasks an attack by a friendly piece standing behind it.
Double Check: Moving a piece both delivers check itself and discovers check from another piece. The defending King must move, as no single move can capture or block two attackers at once.

Checkmate¶

A position where a King is in check and there are no legal moves available to escape the attack.
The game terminates immediately and the checking side wins.

5. Draw Conditions¶

Stalemate: The player whose turn it is has no legal moves available and their King is not in check. The game ends in an immediate draw.
Insufficient Material: Neither player possesses material sufficient to checkmate under any legal sequence of moves:
King vs. King
King and Bishop vs. King
King and Knight vs. King
King and Bishop vs. King and Bishop (where both Bishops are on the same square color)
Threefold Repetition: The exact identical board position occurs 3 times with the same player to move, same legal move set, castling rights, and en passant rights.
Fifty-Move Rule: 50 consecutive full moves (50 by White and 50 by Black) have elapsed without a pawn advance or piece capture.
Mutual Agreement: Both players agree to a draw.

6. Time Controls¶

A game played under clock control terminates in a loss on time ("flag fall") if a player's remaining time reaches zero, provided the opponent has sufficient material to checkmate. If the opponent lacks mating material, the result is a draw.