Mate in 3: queen to b7 (a6·2)
c9-21907naming 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 1990 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 b1, queen a6, rook c3, bishop c1, knight c5, pawn c2 h2 a5 d5 e6.
Black: king b8, queen g8, rook a8 d8, bishop g7, knight d6, pawn g2 b6 f6 a7 c7 d7 e7 h7.
10 white and 14 black pieces are on the board; the puzzle position arises after move 21.
The position in numbers
Black are ahead by 8 points of material (25 against 33; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on b1, the black king on b8.
It is White to move on move 21, with 37 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 5 pawns, Black 8. No file is fully open, so the heavy pieces have to be pried in. Half-open for White: b, f, g.
The White king has 3 empty squares to step to right now — the fewer they are, the closer a mating net.
Solution & explanation
Main line
21. Qb7+ Nxb7 22. Na6+ Kc8 23. Rxc7#
Why it works
- Great move! queen to b7 keeps the pressure (#2).
- Well found: knight to a6 (#1).
- Strong! rook to c7 is the sharp choice (#).
- The line ends in a forced mate in 3.
- If instead Nxb7, then Na6+ and you stay on top.
Move by move
- 21. Qb7+ — queen to b7 with check
- Nxb7 — knight to b7 (capture)
- 22. Na6+ — knight to a6 with check
- Kc8 — king to c8
- 23. Rxc7# — rook to c7 (capture) and it is checkmate
Types in this puzzle
Anastasia's mate
Knight and rook trap the king against the edge of the board.
Anastasia's mate is a knight-and-rook duet at the edge of the board. The knight steals the king's escape squares while the rook mates along the edge file or rank. The textbook picture: a knight on e7 covers g8 and g6, the king's own pawn on g7 blocks the third exit, the king sits on h7 — and the rook mates down the h-file. Watch for it whenever the enemy king hugs the edge; a queen sacrifice on the edge file often clears the way for the rook.
Only move
Everything else loses — find the only move that holds.
An only move is a position where everything loses except one single continuation. You cannot play "by hand" here: run through fundamentally different defenses — run away, block, trade, counterattack — and discard the ones that fail. The hallmark of these puzzles is that the obvious moves lose quickly while the solution often looks strange. First understand exactly what the threat is — then the one saving move reveals itself.
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.
About this position
These pieces come from starting position #950.
SP-950 · RampartGuard — A b- or g-file king and two knights on inner files (b–g).
The king starts on b1, the rooks on a1 and d1, the queen on h1.
From b1 the king makes the longest journey Chess960 allows when castling short: five squares to g1.
The bishops stand on c1 and f1; their long diagonals reach h6 and a6 once the d- and e-pawns step aside.
One second-rank pawn starts with no defender at all: f2.
The setup belongs to the RampartGuard family; read right to left it becomes position 6.
The engine's main line opens with e4, putting a pawn straight into the centre.
Morozov Balance Index: 8 of 100 — class D — largest edge. Engine evaluation of the starting position: +45 centipawns for White (depth 48, 400 000 000 nodes).
Explore position #950Provenance
Mined from the project's engine self-play games.
Pack 014 · SP-950
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