Background: I wrote and use a custom macro in the NoteTab Pro text editor to convert PGN position analysis to XML. The resulting XML is used on my website to display chess puzzles. I need to check for legal moves in some cases. For example, a PGN move might say Rd6 in a position where two rooks can move to d6, but only one of them can legally move to d6 because the other is pinned to its King. I am disinclined to write a macro legal move checker due to the apparent complexity of the task. I do not want to reinvent the wheel.
Ideally, I am looking for an executable that can be called with FEN and next-move parameters, and return a positive or negative result based on the move's legality.