Chilipeppr itself is entirely browser based, so HTML + CSS for the basic elements that you see, and lots of JavaScript for everything else There’s also SPJS which is the tiny “let the browser talk to physical hardware devices” app, this is written in Go, but you don’t need to deal with this if you want to write a new widget/ add features. There are 3 tutorial videos John did at the bottom of the chilieppr homepage showing how to get set up with Cloud9 IDE. My advice, just dive right in - CP is extremely nicely written and the code is well documented.