[yorwba]

Liriliri's Eruda is in the "or similar" category and works directly in mobile browsers: https://github.com/liriliri/eruda With the caveat that if you want to use it on arbitrary websites, you need to be able to inject the script somehow, e.g. using a bookmarklet, which may not be possible in all browsers.

EDIT: Discussion 4 months ago https://news.ycombinator.com/item?id=22968079 , where nxrabl shared the tip of editing an existing bookmark with the javascript code to get it to work in Safari on iOS.