Mate in 2: queen to b8 (b5)
c9-15485naming 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 2: the first move creates an unstoppable threat, the second delivers mate.
A fork made possible by the Chess960 piece placement.
Difficulty 1320 ShuffleRating — club-player level.
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.
Mate in two usually opens with a forcing move — a check, a capture or an unstoppable threat — that strips the king of squares or defenders, so the follow-up mate becomes unavoidable. Look for the first move that leaves the opponent only losing replies.
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 b5, rook g1 e3, bishop d1 d4, knight g3, pawn c2 f2 g2 h2 a4 e4 a7.
Black: king d8, queen f4, rook a8 f8, bishop e7, knight h4 g6, pawn e5 c7 d7 g7 h7.
14 white and 12 black pieces are on the board; the puzzle position arises after move 18.
The position in numbers
White are ahead by 2 points of material (35 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 c1, the black king on d8.
It is White to move on move 18, with 44 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 7 pawns, Black 5. Files fully open (no pawns of either colour): b — natural highways for the rooks and queen. Half-open for White: d.
White hold the bishop pair, an edge in open lines. 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
18. Qb8+ Rxb8 19. axb8=Q#
Why it works
- Great move! queen to b8 keeps the pressure (#1).
- Spot on — pawn to b8 (#).
- The line ends in a forced mate in 2.
- If instead Rxb8, then axb8=Q# and it is mate.
Move by move
- 18. Qb8+ — queen to b8 with check
- Rxb8 — rook to b8 (capture)
- 19. axb8=Q# — pawn to b8 (capture) and it is checkmate
Types in this puzzle
Back-rank mate
The king is locked behind its own pawns — a heavy piece strikes the last rank.
The back-rank mate strikes a king locked behind its own unmoved pawns when a rook or queen crashes onto the last rank. The signs: no escape hole in front of the king, and the back rank guarded by a single piece or by nobody at all. Often that lone guard is deflected or traded off first, and only then comes the invasion. In your own games, make luft in time — one pawn move prevents a sudden catastrophe.
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 2
A forced checkmate in two moves.
Mate in two: your move, any reply, then the mating blow. Start with the most forcing first moves — checks and sacrifices that shrink the opponent's options to almost nothing. Against every single reply you must have a mate ready, so check them all without exception. The common failure is analyzing the pretty defense and forgetting the boring one.
About this position
These pieces come from starting position #801.
SP-801 · BastionScout — Off-centre king plus a rim knight (a/h): 168 positions carry this shape.
The king starts on c1, the rooks on b1 and g1, the queen on e1.
The king already stands on c1, so castling long moves only the rook, from b1 to d1.
A bishop starts in the corner on a1: it has a single diagonal, which the b-pawn unlocks, running out to h8.
One second-rank pawn starts with no defender at all: a2.
The setup belongs to the BastionScout family; read right to left it becomes position 155.
The engine's main line opens with f4.
Morozov Balance Index: 96 of 100 — class A — most balanced. Engine evaluation of the starting position: +11 centipawns for White (depth 42, 400 000 000 nodes).
In 50 self-play games White scored 51.0% (95% CI 37.6–64.3%).
Explore position #801Provenance
Mined from the project's engine self-play games.
Pack 010 · SP-801
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