what did you mean by zero-latency developer tool? it is neither open source, nor it does things that instill confidence; i used uuid gen, and url formatter (pasting the amz product url - its output is rather useless);
"Achieving" latency using local JS is not hard, just do some heavy compute and/or do the same via the browser's layout engine.
Try and do some real work in JS, for example, generate Sudokus, render raster images from DOM fragments, whatever: you'll see latency.
If you want non-blocking latency (like from a network request), use asnyc APIs and a Worker or other natively non-blocking API. Or simply a Promise wrapping a setTimeout.
But latency in synchronous and local JS is an everyday problem. So I think your phrasing is wrong.
Nitpick: the image compressor page seems to show the instructions for the IP address converter.