Nice! It even follows successive redirects, e.g., if t.co redirects to bit.ly that redirects to something.com, then mouse over the t.co link gives you the final something.com destination full URL. :-)

(I suggest adding some screenshot so that users know what kind of visual hint to expect...)

I trust in the developer's statement that no data is collected and being open-sourced is a plus for trusting this even if one can't (don't know how to) check it.