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Is there a mate here?
Paste a position as an SFEN, choose how many plies to look, and the engine’s mate solver searches for the shortest forced checkmate and plays it out on the board. It is the same solver that checks the app’s puzzles.
What it looks for
A forced mate: a sequence where every move of the side to play is check, every reply of the defender is answered, and the king is mated at the end whatever the defender does. The search is depth-first proof-number search, the algorithm tsume solvers use, and it reports the shortest mate it can prove. Plies count both sides’ moves, so “mate in 5” is three of your moves and two replies.
Writing an SFEN
Nine ranks from the far side, separated by slashes; a letter per piece (K R B G S N L P, uppercase for black, lowercase for white, a plus sign before a promoted piece) and a digit for empty squares; then whose move it is (b or w); then the pieces in hand (a dash for none, otherwise letters with counts, like 2G3P); then the move number. The start position is lnsgkgsnl/1r5b1/ppppppppp/9/9/9/PPPPPPPPP/1B5R1/LNSGKGSNL b - 1. The KIF viewer prints the SFEN of any position in a game, and most shogi programs copy one to the clipboard.
Limits
The search runs in your browser with a budget of about a million and a half nodes, which finds most mates up to seven plies in a moment and many longer ones. When it says nothing was found, it means nothing was found within that budget: a deep tsume may need more. It does not evaluate positions, only mates; for “who is winning”, the app’s review does that.
The solver plays for you in the app.
Every puzzle is checked by it, the bot never misses a mate it can see, and the review names the mates you missed.