SimulChess Rules

Overview

SimulChess is a variant of chess where both players move simultaneously rather than alternating turns. This creates unique strategic considerations and potential conflicts when moves interact with each other.

Basic Rules

  1. 1 All standard chess rules apply except for turn order.
  2. 2 Both players submit their moves at the same time without knowing what the opponent will play.
  3. 3 After both moves are submitted, they are resolved according to the conflict resolution rules using a fast/slow piece movement system.
  4. 4 If a move is illegal in the current position, it is rejected.

Fast/Slow Movement System

Pieces are divided into two categories based on their movement characteristics:

Movement Categories
Category Pieces Movement
Fast Instant movement
Slow Gradual movement
Movement Rules
Fast Pieces (Pawns, Knights)
  • Advantage: Move instantly, cannot be intercepted
  • Vulnerability: Capture attempts fail if base is attacked
  • Escape Rule: Non-capture moves succeed even if base is attacked
Slow Pieces (Rooks, Bishops, Queens, Kings)
  • Advantage: Attack succeeds even if base destroyed
  • Vulnerability: Can be intercepted during movement
King Special Rule: Kings survive collisions with other pieces. King vs King collision = draw.

Conflict Resolution

Resolution Order
  1. Base Attack Check: Check if any fast pieces have their starting squares attacked - capture attempts fail, escapes succeed
  2. Path Interception Check: Check if any slow pieces are blocked
  3. Collision Resolution: Handle pieces targeting the same square
  4. Move Execution: Apply successful moves and handle captures
Capture Rules
Standard Captures

A moving piece can capture a stationary piece by moving to its square.

Base Attacks

If a piece attacks the starting square of a fast piece (pawn or knight): capture attempts are cancelled, non-capture moves (escapes) succeed.

Path Interception

Slow pieces can be blocked by any piece landing in their movement path. The intercepting piece is destroyed, the slow piece stops at the interception point.

Chain Captures

If a slow piece is captured while attempting to capture another piece:

  • The slow piece is captured
  • The piece it was targeting is also captured (chain capture)
  • Fast pieces don't get chain captures when their base is attacked

Examples

Scenario: White's knight on e4 attempts to capture on f6. Black plays Bxe4, attacking the knight's base.
Result: Knight's capture attempt is cancelled, knight is captured.

Scenario: White's rook moves from a1 to a8. Black's knight moves to a4.
Result: Rook stops at a4, knight is destroyed.

Scenario: White's king moves to e5, Black's rook also moves to e5.
Result: King survives, rook is destroyed.

Scenario: White's queen on d1 moves to capture Black's rook on d8. Black's knight simultaneously captures White's queen on d1.
Result: Both the rook and the queen are captured (slow pieces complete their captures even when their base is attacked).

Special Cases

Check and Checkmate

SimulChess uses a hybrid approach for game ending conditions:

Classical Checkmate Check
  • At the start of each turn, the game checks for classical checkmate conditions
  • If a king is in checkmate at the start of the turn, that player loses immediately
  • If both kings are in checkmate at the start of the turn, the game is declared a draw
  • This check happens before any moves are processed
King Capture Rules
  • Players can move into or remain in positions where their king could be captured
  • A player also wins by capturing the opponent's king during simultaneous move resolution
  • The game continues until either a checkmate condition is detected at turn start or a king is captured
Castling

Castling follows normal chess rules but is subject to the conflict resolution rules above. If an opponent's move would prevent castling, the castling move is rejected.

Time Controls

In longer time controls (>10 minutes per turn), the system may resolve and apply a move even if only one player has submitted, allowing for correspondence-style play.

Strategy Tips

  • Use fast pieces: Pawns and knights move instantly but are vulnerable to base attacks
  • Protect piece bases: Fast pieces fail if their starting square gets attacked
  • Plan for conflicts: Anticipate where your opponent might move
  • Chain captures: Set up situations where capturing your piece backfires
  • King safety: Kings survive collisions but can still be captured normally
  • Path blocking: Use pieces strategically to intercept slow piece movements
Start Playing SimulChess