How Vimmy Is Your Vim Mode?

I was in a programming interview the other day where the interviewers and I were sharing an online code pad (either CoderPad or CodeSignal) that offered a "Vim mode", but when I tried to use a Vim feature, it didn't behave as I expected! Driven by curiosity, I took a deep dive into what Vim features are offered on what sites.

Overall the story is really impressive for most of these sites! I also tried out a couple of IDEs (PyCharm CE and VS Code, both with their Vim plugins set up) and they also performed well overall.