Eruda
Console for mobile browsers
..., if not set, it will append an element directly under html root element. Choose which default tools you want, by default all will be added. There are several available plugins, like eruda-fps, which displays page fps info, eruda-features, which will let you see feature detections, eruda-timing, to show performance and resource timing, eruda-memory, to display page memory info, eruda-code, to run JavaScript code, and many more.