Attack on the uncastled king: queen to b7 (a6·3)
c9-25507naming 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.
Uncastled king: the enemy king is stuck in the centre — punish it before it castles.
Difficulty 1450 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.
An uncastled king in the centre is a standing target. Look for ways to open the central files and diagonals against it with checks and threats before it can shelter — every tempo the king spends in the middle is a chance for a combination.
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 a6, rook b2 a4, bishop c3, knight e1, pawn a2 c2 d2 h2 e3 g3 c6.
Black: king c8, queen g8, rook b7 f8, bishop d8, knight h4 d6, pawn e4 f5 h5 b6 c7.
13 white and 12 black pieces are on the board; the puzzle position arises after move 21.
The position in numbers
Black are ahead by 1 points of material (32 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 c8.
It is White to move on move 21, with 40 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 7 pawns, Black 5. No file is fully open, so the heavy pieces have to be pried in. Half-open for White: b, f.
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
21. Qxb7+ Nxb7 22. Ra8#
Why it works
- Best move. queen to b7 is exactly what the engine plays (#1).
- Well found: rook to a8 (#).
- The line ends in a forced mate in 2.
- If instead Nxb7, then Ra8# and it is mate.
Move by move
- 21. Qxb7+ — queen to b7 (capture) with check
- Nxb7 — knight to b7 (capture)
- 22. Ra8# — rook to a8 and it is checkmate
Types in this puzzle
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.
Sacrifice attack
Give up material to unleash a decisive attack.
A sacrificial attack gives up material on purpose to rip the king's shelter open and launch a decisive assault. The sac is sound when you get concrete assets in return: open lines to the king, tempi, pieces ready to pour in. The signs: a poorly sheltered king, your forces aimed at its home, defenders stranded far away. The iron rule is to calculate, not hope — once the material is gone, there is no way back.
Uncastled king
The king lingered in the middle — punish the delay.
Punishing the uncastled king: your opponent delayed castling, and now his king is stuck on its starting square under fire. In Chess960 this is deadlier than in classical chess — the king may start in the center or near the edge, and the familiar defensive setups simply do not apply. The signs: the victim still holds castling rights, and the files toward his king are half-open. Open lines before the king manages to hide.
About this position
These pieces come from starting position #833.
SP-833 · BastionScout — King shifted to c or f, with a knight committed to the corner from move one.
The king starts on c1, the rooks on b1 and f1, the queen on g1.
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 123.
The engine's main line opens with f4.
Morozov Balance Index: 92 of 100 — class A — most balanced. Engine evaluation of the starting position: +12 centipawns for White (depth 49, 400 000 000 nodes).
Explore position #833Provenance
Mined from the project's engine self-play games.
Pack 011 · SP-833
Similar puzzles
In your browser or in the Android app. Nothing to install · Free, no ads