Interpreting results

Hi, I am looking at the JSON response from the tests and wondering if there is documentation about what the metrics mean and what their units are etc?

Most of them are pretty clear but a few are not so. e.g. is visual complete on screen only or the entire page? Is the unit of image_total bytes?

Some descriptions will be really helpful. Thanks.

The book by Rick Viscomi, Andy Davies, Marcel Duran, “Using WebPageTest Web Performance Testing for Novices and Power Users” contains the information you’re looking for. Nowhere else on the internet is this information available afaik and I’ve been looking for the exact same thing for a few days now.

Unfortunately, the book doesn’t include a description of every metric, only a few.

Most metrics are in milliseconds, some are counts (requests) and the bytes are in bytes (may be KB but pretty sure it’s bytes). You can verify by looking at the UI for a given test.

The visual metrics (start render, visually complete, speed index, etc) are calculated using video capture of the browser viewport and only measure the visible part of the viewport.