Exactly! I'm a huge fan of CodePen/JSFiddle/etc., but wanted to have an experience that let me take advantage of my existing editor setup, in order to experiment with ideas or learn new things. I built CodeSwing to "scratch my own itch", and I'm keen to hear if it's useful for others as well :D

Regarding the Golang playground: is this what you're thinking about? https://play.golang.org/. CodeSwing is a general-purpose "interactive coding environment", and therefore, I'd love to expand it over time to include more languages. Right now, it's limited to web scenarios, but that's simply where I started.

Would it be useful to be able to create a new Go/Rust swing inside VS Code, and have it automatically run your code, and display stdout in a console window as you type? Or did you have something else in mind?