Three measurements, three usual causes
| Metric | Usual WordPress cause |
|---|---|
| Slow largest content paint | An unoptimised hero image or slider |
| Layout shifting | Images without dimensions, or late-loading fonts |
| Slow interaction | Too much JavaScript, usually from plugins |
Each has a small number of usual causes, which makes diagnosis quicker than it sounds.
Fix the largest element first
Find what the largest content element actually is — usually a hero image or a heading. Then make it arrive faster: size it properly, load it eagerly, and do not put it behind a slider.
Sliders are the most common cause of a poor largest content paint on WordPress. They are also rarely worth what they cost.
Stop the layout jumping
- Width and height on every image, so space is reserved
- Reserved space for ads, embeds and banners
- Font loading that does not cause a visible swap
- Nothing inserted above existing content after load
Reduce the JavaScript
Interaction delay is caused by the browser being busy. On WordPress that is usually plugin scripts loading on every page whether needed or not.
Load scripts only where they are used. That is a per-plugin fix and it is the main work here.
Measure real users, not just tests
Laboratory tests are useful for diagnosis; field data from real visitors is what actually counts.
A site that tests well on fibre and poorly on a phone on mobile data has a real problem regardless of the score.