Puzzle vT5y8_M — ELO 871
This is a Black-to-move puzzle rated 871 ELO. The first move is c6a5, tagged with 10 interpretable concepts and Lichess themes: hookMate, mate, mateIn1.
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Position
Black to move. ELO 871. Themes: hookMate, mate, mateIn1, middlegame, oneMove.
FEN: 4qb1r/1ppkp1pp/2npNn2/Q4P2/3P4/5N2/PP4PP/1KR4R b - - 0 15
Show solution (2 ply)
Try to find the move yourself first — look for the rarest concept firing on this position before peeking. Solution sequence: c6a5 c1c7
Concepts that fire on this position
Our SAE pipeline tagged this position with 10 active features. Each links to a page documenting that pattern in detail.
Why this puzzle is hard
The rarest pattern firing here is A square is attacked by at least 3 white pieces and at most 1 black piece, and…, which appears in only 42 of our 9,950 puzzles (0.42%). Rare patterns tend to be the bottleneck — players who haven't internalised them will fail this puzzle even when their tactical calculation is otherwise solid.
The puzzle's Lichess ELO of 871 reflects this: solvers below that rating typically miss the cue entirely.
Similar puzzles
Puzzles sharing the most concept tags with this one — a stronger signal than theme overlap because it reflects the actual patterns Leela recognises.
Train this pattern
Click through to the Climbchess trainer to attempt the position interactively against the same Leela network that tagged it. The trainer adapts difficulty using your live concept-recognition profile — it surfaces puzzles tagged with concepts you've been missing, not random brawls.
If you want the underlying methodology, the how-it-works page walks through the SAE training run, the labelling pipeline, and the puzzle-tagging procedure end-to-end.
Frequently asked
What is the rating of this puzzle?
871 Lichess ELO. Solvers below that rating typically miss the key cue.
Which side moves first?
Black to move; the first move of the solution is c6a5.
What concepts does it train?
10 SAE-derived patterns including A white knight on a stable central or near-central square…; Detects positions with an active white knight on an…; Detects white king safely castled on the back rank….
Can I attempt it without an account?
Yes — Climbchess requires no signup or email. Click the trainer link to play the position interactively.