The starting position
Each side sees the squares its own pieces could legally move to (under regular chess rules), plus the squares they stand on. Everything else is fog.
What you see
Here's the same rule, piece by piece.
Vision moves with pieces. When a piece moves, the squares it used to cover go dark (unless another piece still sees them), and the squares it now reaches light up.
Notice the rook on d7 sees the queen on b7 and the king on h7, but not a7. A piece's vision ends where its movement ends.
Win condition: king capture
The game ends when a king is captured. No check, no checkmate, no warning.
Draws
Mistboard auto-draws games on threefold repetition (same true position three times, same side to move, same castling and en-passant rights) and the 50-move rule (fifty full moves with no pawn move or capture). Both apply to the true position, not either player's view. A side with no moves at all, every piece blocked, also draws. Otherwise you must move, even if every move walks into attack. There is no insufficient-material draw.
Edge cases
Castling
A king may castle out of, through, or into check.
Pawn vision
Pawns see forward push squares when those squares are empty. They see diagonal squares only when an enemy piece is actually there to capture.
White does not see a4 or b4: black pawns block those pushes, so they are not legal moves. Some rulesets reveal blocked pawn squares; Mistboard does not.
En passant
En passant is chess's strangest move, so our vision rule bends for it: the capturing pawn sees the captured pawn on its adjacent square. The window is one move only. Pass on the capture and the chance is gone.
A sample game
Here is a complete game between Mistboard's engine and a human, shown from both player views and the server's full position.
An engine game
Misty against itself at 30 seconds a move, shown with the whole board visible. Black wins White’s queen for a rook on move 10, but on move 27 White’s rook lands on e8 and Black’s king steps to d8 beside it. Fog chess has no check to warn it, and 28.Rxd8 captures the king.
The companion study has eleven of these games, and shows each side’s fogged view move by move.
Common questions
- Can the bot see through the fog?
- No. Misty never sees the whole board. Each move it receives only what its own pieces can see, the same fog you play under, and it treats the rest as a set of boards that could all be true. The server that enforces this is open source, and tests fail the build if a hidden square ever leaks into what the engine is sent.
Play on Mistboard
You can castle out of, through or into check, and nobody tells you when your king is attacked. No account needed.