Mate in 3: queen to b8 (a8·3)
c9-28046naming 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.
Difficulty 1630 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.
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 e1, queen a8, rook d1 g1, bishop a7, knight a3 d4, pawn a2 b2 h2 c3 f4 g5.
Black: king e8, rook h8, knight b8, pawn h5 g6 e7 f7.
13 white and 7 black pieces are on the board; the puzzle position arises after move 20.
The position in numbers
White are ahead by 22 points of material (34 against 12; pawn = 1, knight and bishop = 3, rook = 5, queen = 9) — the tactic has to convert or outweigh that.
The white king stands on e1, the black king on e8.
It is White to move on move 20, with 45 legal replies to weigh — only the line that keeps the advantage solves the puzzle.
White keeps 6 pawns, Black 4. Files fully open (no pawns of either colour): d — natural highways for the rooks and queen. Half-open for White: e.
The White king has 6 empty squares to step to right now — the fewer they are, the closer a mating net.
Solution & explanation
Main line
20. Qxb8+ Kd7 21. Ndb5+ Kc6 22. Qb6#
Why it works
- Best move. queen to b8 is exactly what the engine plays (#2).
- Spot on — knight to b5 (#1).
- Precise: queen to b6 is the top choice (#).
- The line ends in a forced mate in 3.
- If instead Kd7, then Ndb5+ and you win the knight.
Move by move
- 20. Qxb8+ — queen to b8 (capture) with check
- Kd7 — king to d7
- 21. Ndb5+ — knight to b5 with check
- Kc6 — king to c6
- 22. Qb6# — queen to b6 and it is checkmate
Types in this puzzle
Supported queen mate
The queen delivers mate face to face, protected by a friend.
The supported queen mate is the most common pattern of all: the queen lands next to the king and mates because a friendly piece or pawn protects her. The king is helpless — capturing is impossible, and the queen covers every neighboring square herself. Hunt for a protected square beside the enemy king: a knight, bishop or pawn eyeing it turns her invasion into mate. Verify one thing — that the square really is defended, or the king eats her.
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.
Win the pinned piece
The pinned piece cannot run — attack it again and win it.
A pinned piece cannot flee, which means you can win it outright by attacking it one more time. Count attackers against defenders: if you outnumber them, the piece is yours. The best extra attacker is a pawn, since it costs less than anything it might capture. Do not rush the capture — build up the pressure first, then harvest.
About this position
These pieces come from starting position #86.
SP-86 · ThroneScout — The king starts on d or e while at least one knight begins in a corner.
The king starts on e1, the rooks on d1 and g1, the queen on h1.
The queenside rook already stands on d1, so castling long moves only the king, from e1 to c1.
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: a2.
The setup belongs to the ThroneScout family; read right to left it becomes position 870.
The engine's main line opens with d4, putting a pawn straight into the centre.
Morozov Balance Index: 57 of 100 — class B — balanced. Engine evaluation of the starting position: +34 centipawns for White (depth 47, 400 000 000 nodes).
In 50 self-play games White scored 50.0% (95% CI 36.6–63.4%).
Explore position #86Provenance
Mined from the project's engine self-play games.
Pack 012 · SP-86
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