MeasureIt Safari Extension

Name: MeasureIt Author: Kevin Freitas | Website | Download Description: Creates an overlay ruler on the current web page showing pixel width and height for the box drawn.

This extension that has been available on Firefox for years has been ported by the author to Safari (and Chrome).

Notes:

After installing, it wouldn't work unless I opened a new tab or reloaded a webpage. Restarting Safari on my system was not required. To clear the ruler, click the toolbar button a second time. This extension doesn't work for me on all websites, e.g., Gmail.

There are some additional features this extension could benefit from, like ratio of W:H, dividers to break the image into thirds (via the Rule of Thirds and the Golden Ratio in photography), diagonal measurement, and single click to show the dimensions of a design element (div or image).