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7 guides

Website Speed and Core Web Vitals Guides

Almost every performance problem gets diagnosed before it gets measured, which is why so many of them get fixed in the wrong place. The guides in this cluster are ordered around measuring first.

The distinction that resolves the most confusion is lab versus field. A Lighthouse run is a single test on simulated hardware, and it is repeatable and useful for comparing changes. Field data comes from real visitors on real devices and networks, and it is what Core Web Vitals reports. The two disagree routinely, and neither is wrong when that happens; they are measuring different things. Reading a score without knowing which one you are looking at is how teams end up optimising something their visitors never experience.

From there the guides work through the layers where time actually goes: images and media, fonts, third-party scripts, render-blocking work, and the data fetching behind the page. Most sites are slow in one or two of these, not all of them, which is why the diagnosis is worth the hour it takes.

A note on scores. Our own commercial terms use a 90+ Lighthouse acceptance target on named pages, verified across recorded runs before handover. That is a lab acceptance criterion, not a promise about rankings, traffic, or field metrics after later changes.

To see where a specific site is losing time rather than reading about it generally, start with a free performance audit of your own site.

Every guide in this topic

Past the reading stage?

These guides describe the decision. If you have made it and want the work scoped against your own site, the commercial terms, acceptance criteria, and exclusions are on one page.

See the free site audit