Pretty easy once you know it but tough to find at first: Go to Settings ► About ► Software information ► More, then tap 7 times on “Build number”. You’ll now be able to activate the Developer options in Settings. Source.
More about remote debugging with Chrome.
Edit: In order for it to work, to be able to debug from my computer the site i’m viewing on my mobile, HTC One in that case, i had to download and fire up the HTC Sync Manager. You can download it here. Then follow the steps listed on the remote debugging page link (second in this page) and don’t hesitate to switch the HTC Sync Manager on and off as well as the Developer mode on the phone for the desktop Chrome to see the mobile Chrome. Still with me?
You’ll then be able to see the device connected, as well as the tabs open on them, be able to switch tabs from the desktop Chrome, reload, close…
… and inspect!
Yup, that picture is a screenshot of the phone being inspected by the desktop Chrome live. you can see the usual blue, orange, green and other inspect helpers moving live on the phone. Pretty sweet.
Ok, in the end this “ILT” is more of a post, but eh, it’s fine here because in the end it’s a good thing i learned. 🙂