Responsive images are essential to any image-heavy website with an eye on performance. Due to the large variety of viewport sizes and device pixel ratios, they are also very time-intensive to test. Luckily, the heroes over at Filament Group have built a tool to help make the testing process easier.

A command line tool to measure the efficiency of your responsive image markup across viewport sizes and device pixel ratios.

I assume the project name is a nod to weirdo musician and tech experimenter Imogen Heap.