I am really interested in how to draw the algorithm search space, possibly during the execution. This is especially useful for educational purposes.
I am mostly interested in CH, but also Dijkstra, A* and others are very relevant.
I have used MiniGraphUI (desktop/swing):
But in recent times you should also try deck.gl for this:
E.g. use our new /spt endpoint here https://github.com/graphhopper/graphhopper/pull/1577
Or our debugging tiles view: https://github.com/graphhopper/graphhopper/pull/1572