The Dovetail Mate, also called Cozio’s mate, is a queen checkmate where the king’s two diagonal escape squares are both blocked by its own pieces.
The queen delivers check from a square right next to the king, supported so it can’t be captured. The king’s two diagonal flight squares are sealed by its own pieces, which fan out behind it like a dove’s tail.
It’s closely related to the Swallow’s Tail Mate — the difference is just which pair of escape squares the king’s own pieces happen to block. Both rely on a supported queen and a king hemmed in by its own men.
The supporting piece is essential: without something defending the queen, the king would simply capture it. Spot a king boxed in on two diagonals and a queen that can arrive with protection, and the mate is there.
Both are supported-queen mates with the king blocked by its own pieces. In the Dovetail the blocked flights are diagonal; in the Swallow’s Tail they’re the two rear squares.
Because it gives check from right next to the king. If nothing defended it, the king would just capture the queen instead of being mated.
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