Here's a chess puzzle that gave a confusing response. https://chesspuzzle.net/Puzzle/52112
[FEN "5R2/1p6/p4Ppk/3r4/7p/1P6/P7/1K6 w - - 0 1"] 1. Rh8+ Kg5 2. f7 Rf5 3. f8=R
If you play
f8=Q in this final position, you will not fail the puzzle, but be told "There is a better move..." (
It seems inevitable that the black captures the promoted piece, and the result is the same after white recaptures.
f8=Q was played in the game. https://www.chess.com/games/view/15563079
What is more curious, is that I have played other puzzles on this site that allow multiple moves in a position for continuation, and my assumption therefore was that it only suggests a "better move" when your move doesn't change the theoretical outcome of the game, but gives significantly lower advantage (i.e. still decisively winning, but slower). This would suggest that chesspuzzle.net has evaluated
f8=Q to be an inaccuracy of some sort.
Is there any reasoning to be found for this? Or is it just a strange computer evaluation?
I have tried inputting the position on the analysis board on lichess.org, and it flip flops between the two moves as the depth builds, but eventually starts showing
f8=Q with a consistent advantage. (The opposite of chesspuzzle.net)
This seems strange also, as in my perhaps naïve reasoning explained initially, both moves should be identical.