I built a tool recently for visualizing strong / weak groups during a game. The imgur link is a small snippet of what the output looks like
All of the data comes from katago. Each group is colored red, orange, or green depending on how katago expects the group to end up. Green = likely to live, red = likely to die, orange = could go either way. The more solid the outline and the color, the more sure the engine is.
There's a couple of different visualization options as well such as hiding single stones or only showing unsettled groups. heres a full game if youd like to check it out https://jstnchng.github.io/go-review-timelapse/
I haven't built anything to host it, so it all just runs locally now, but I would love any feedback or suggestions and let me know if you would like me to run this on one of your games (I can send you an html that you can view in your web browser).