What this check inspects
Shipwork queries the Chrome UX Report for your origin and reads the 75th percentile of Largest Contentful Paint, Interaction to Next Paint and Cumulative Layout Shift. It reports each metric with a verdict, the share of mobile traffic, and the collection period. Origins without enough Chrome traffic have no data, and it says so rather than inventing a number.
What a failure means
A metric rated poor is an error and one rated needs improvement is a warning. Because the verdict is at the 75th percentile, it reflects the slower quarter of your visitors, not the average. Mobile share matters: if most traffic is on phones, mobile performance decides the verdict.
How to fix it
- Fix the largest element first. LCP is usually a hero or product image, so serve it in a modern format at the right size and do not lazy load it.
- Reserve space for images and embeds so Cumulative Layout Shift drops.
- Reduce main-thread work from third-party scripts to improve Interaction to Next Paint.
- Re-measure after each change. Field data updates on a rolling window, so it takes days to reflect a fix.
A typical failure, worked through
The setupA store serves a 1.8MB hero image as a PNG at desktop dimensions on mobile, and injects a chat widget that loads before the image.
What the check reportsLCP at the 75th percentile is poor on mobile, while desktop is good. The check reports the mobile share that makes this the metric that matters.
The pointField data is not a lab score, so a change that looks good in a single test may not move the p75. Target the slowest quarter of real visits.