Pulse vs PageSpeed Insights

Use PageSpeed Insights when

It is the better tool for one important thing, and it would be dishonest to bury it. PageSpeed Insights reports field data from the Chrome UX Report, which is what Google actually assesses your pages on. If your question is whether a URL passes Core Web Vitals, that is the authoritative answer and Pulse cannot give it to you. It is also free, run by Google, and needs no explanation to a client.

Use Pulse when

Field data tells you that a page is slow. It does not tell you that a single hero image is being downloaded at 3840px and painted at 1280px, costing 1.4 MB. Pulse exists for the second question. It inspects the rendered DOM, the network log and the trace, then ranks every finding by the saving it actually measured on your page, so the top of the list is the thing worth doing first rather than the first audit that happened to fail.

Side by side

Why the scores differ

Lighthouse scores performance from five timing metrics and nothing else. Pulse weighs those same timings but also accounts for total page weight, request count and third party bytes, because a page can hit good timings on a fast connection while shipping several megabytes that punish a real visitor on a phone. Both numbers appear on every Pulse report, side by side, and the breakdown shows where each point was lost.

Neither is presented as the other. If you need the number Google uses, read the Lighthouse column.

The honest answer

Use both. Check PageSpeed Insights to see whether real users are having a bad time, then run Pulse to find out why and to verify the fix, because field data takes 28 days to reflect a change and lab data reflects it immediately.