Solution 1:

I found this app, but not sure how extensive is it compared to a traditional web inspector

Ergo Web Tools by James Finley https://appsto.re/us/3vdC_.i

Let me know if you've found an alternative or something

Solution 2:

I have been using MIHTool: https://www.mihtool.com/ - It’s not quite as good as being on Chrome on a Desktop but it gets some of the job done!

I also use Inspect Browser https://itunes.apple.com/us/app/inspect-browser/id1203594958?mt=8

Solution 3:

You may try the Gear browser. It can inspect elements, view source, pickup color, full-screen snapshot, and more, and also available on both iPhone and iPad.

https://gear4.app