Mate in 3: queen to b5 (a4·2)
c9-26238naming tag (square·N)Opens in the app if installed, otherwise downloads the APK.
The tactical motive
Chess960 twist: use the unusual starting setup of the pieces.
Mate in 3: a forced sequence that ends in checkmate.
A fork made possible by the Chess960 piece placement.
Difficulty 1760 ShuffleRating — for advanced tacticians.
White to move — find the best continuation
How to recognize this tactic
In Chess960 the pieces start on unfamiliar squares, so tactics appear earlier and from unusual angles. Do not trust classical patterns — read the actual lines of the bishops, the rooks and the queen from where they really stand in this position.
In a mate in three every move must be forcing; the defender should never get a free tempo. Find the check or threat that herds the king, calculate the single defence to each, and confirm the net closes on the third move.
A set-up fork needs one preparing move before the fork lands — a check that drives the king onto the forking square, or a capture that lines the targets up. Find the preparation first, then the fork it makes possible.
General method: before you move, list the forcing candidates — every check, every capture, every direct threat — and calculate those first. The solution to a tactic is almost always among them.
Position on the board
White: king c1, queen a4, rook d5, bishop e1 e2, knight f1 c3, pawn b2 c2 d2 e3 e5.
Black: king b8, queen h8, bishop b4 e8, knight f5 c6, pawn h3 g4 h5 c7.
12 white and 10 black pieces are on the board; the puzzle position arises after move 24.
The position in numbers
White are ahead by 6 points of material (31 against 25; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on c1, the black king on b8.
It is White to move on move 24, with 43 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 5 pawns, Black 4. Files fully open (no pawns of either colour): a, f — natural highways for the rooks and queen. Half-open for White: g, h.
The White king has 2 empty squares to step to right now — the fewer they are, the closer a mating net.
Solution & explanation
Main line
24. Qb5+ Kc8 25. Qa6+ Kb8 26. Rb5#
Why it works
- Great move! queen to b5 keeps the pressure (#2).
- Well found: queen to a6 (#1).
- Precise: rook to b5 is the top choice (#).
- The line ends in a forced mate in 3.
- If instead Kc8, then Qa6+ and you stay on top.
Move by move
- 24. Qb5+ — queen to b5 with check
- Kc8 — king to c8
- 25. Qa6+ — queen to a6 with check
- Kb8 — king to b8
- 26. Rb5# — rook to b5 and it is checkmate
Types in this puzzle
Hook mate
Rook, knight and pawn form a hook the king cannot escape.
The hook mate is a three-piece construction: the rook mates, the knight guards the rook, and a pawn guards the knight. The rook strikes the king at close range along a line, the knight stands diagonally nearby stealing the escape squares, and the pawn anchors the chain. The pattern usually appears near the edge after a rook invasion. Build it link by link — first plant the knight under pawn protection, then crash in with the rook.
Setup fork
The random setup allows a fork that classical chess never sees.
A setup fork is a double attack that exists only because of the unusual starting squares — in classical chess these targets never stand side by side. Look for pairs of undefended pieces on your opponent's back rank and for squares from which a knight or pawn hits both at once. Such forks usually appear within the first moves, before the pieces disperse. In every new position, note right away which starting pieces are defended by no one.
Mate in 3
A forced checkmate in three moves.
Mate in three is a forced staircase: each of your moves narrows the opponent's choices, and the third one ends the game. Look for the start among checks and sacrifices — quiet first moves are rare in mating problems, but deliciously sneaky. Keep the tree in your head: every defense gets its own branch. Do not stop calculating after move two — see the final mating picture with your own eyes.
About this position
These pieces come from starting position #665.
SP-665 · BastionGuard — Off-centre king (c/f), no knight on the a- or h-file.
The king starts on c1, the rooks on a1 and f1, the queen on h1.
The king already stands on c1, so castling long moves only the rook, from a1 to d1.
The bishops stand on d1 and e1; their long diagonals reach h5 and a5 once the e- and d-pawns step aside.
The pawn on b2 is defended by the king alone — the same soft spot f2 is in the classical setup.
The setup belongs to the BastionGuard family; read right to left it becomes position 201.
The engine's main line opens with g4.
Morozov Balance Index: 42 of 100 — class C — noticeable edge. Engine evaluation of the starting position: +22 centipawns for White (depth 44, 400 000 000 nodes).
In 50 self-play games White scored 56.0% (95% CI 42.3–68.8%).
Explore position #665Provenance
Mined from the project's engine self-play games.
Pack 013 · SP-665
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