Read the per-site breakdown#

The sections at the top of the Performance tab measure the session as a whole. Below them, a per-site breakdown repeats the same metrics for each site the session talked to. It turns a single set of totals into an answer to one question: which site is responsible for this?

How the breakdown groups traffic#

The breakdown groups requests by their registrable domain, so every request to a site and its subdomains lands in one group. It orders the groups by request count, busiest first. Each group shows how many requests it holds. The site that did the most work is at the top.

Read one site's metrics#

Each group expands to the same sections you get for the whole session, scoped to that site alone: page vitals, errors, hotspots, caching and compression, protocol, party split, and resource timing. A group tells you how one site behaved, not how the session behaved on average.

This is how you attribute a problem. If the session as a whole looks slow or heavy, open the breakdown, find the site at fault, and read its section. It tells you whether the cost was slow responses, large downloads, poor caching, or a high request count.

For what each section means, see reading the metrics.