Online program for FEN recalculation I am looking for any online tools that can recalculate the the FEN values based on the current FEN and a given step. Are there any such tools or should I write one on my own.
I don't think this is exactly what you're looking for, but it's at least a start.

The Analysis Board at chess.com allows you to paste in a FEN, make a move, then go to the Position Setup tab and copy the FEN.