Viewler is a free Chrome add-on developed by blobbybilb that provides a simple and unique way to measure web page elements using viewport-based units, vw and vh. Unlike other page rulers that rely on pixels, Viewler allows users to accurately measure elements using these responsive units.

With Viewler, users can easily determine the size of various elements on a web page by simply hovering their mouse over the desired area. The add-on displays vertical and horizontal rulers that dynamically adjust based on the viewport size, providing real-time measurements.

One standout feature of Viewler is its mouse tracking marks, which indicate the precise location of the mouse on both rulers. This feature enhances accuracy and makes it easier to measure elements with precision.