[fastball]

I would pay a monthly subscription for a playground that makes it very easy for me to quickly prototype and test across different browsers.

For quick JS prototyping I use RunJS a fair bit, but it is purely for JS so I can't test HTML/CSS. I've also tried Quokka for the same use case but it didn't work very well for me either (having to create files in my editor actually felt kinda annoying somehow).

I also do a decent amount of performance benchmarking, but all the websites for that right now are pretty meh (takes a while to figure out how to get libs imported, assuming they actually work, seems many JS benching sites are abandoned). And most of all they only test in my browser. While building the test suite that's good, but once I'm happy with it I'd like to be able to click a button which will bench my suite in Chrome / Firefox / Safari.