Understand the three measurements
Largest Contentful Paint concerns when the main visible content appears. Interaction to Next Paint concerns responsiveness to user interactions. Cumulative Layout Shift concerns unexpected movement of visible elements. The published good thresholds are LCP at most 2.5 seconds, INP at most 200 milliseconds and CLS at most 0.1, evaluated at the 75th percentile of field visits.
Read the conditions behind a result
Device, network, cache, page assets and third-party services affect measurements. A Lighthouse run is a controlled diagnostic sample, not a complete record of all visitors. Field data may be unavailable for a new or low-traffic page. Record that absence instead of replacing it with a lab score under the same label.
Connect fixes to an observable problem
A slow main image, a heavy interaction script and a late-moving banner need different remedies. Identify the affected page and metric before changing the design. Retest the altered behaviour under comparable conditions and review field evidence when enough exists. A perfect score should not take priority over accessible controls or information visitors need.
A practical next step
What to prepare.
- Evidence label
Record whether a result is laboratory testing or field data.
- Test conditions
Keep device, network, URL and date alongside each measurement.
- Targeted fix
Link the proposed change to the loading, interaction or stability problem it addresses.
Questions worth asking.
Is a Lighthouse score a Core Web Vitals pass?
A lab score alone does not establish a field assessment. Keep the two types of evidence distinct.
Can a new site have field data immediately?
It may not have sufficient real-visit data. That limitation should be reported clearly.
Does better speed guarantee more enquiries?
No. Speed supports usability, while offer, relevance, trust and many other factors affect enquiries.
Sources & further reading.
Primary documentation for the factual background. Our project recommendations depend on your requirements.
web.dev: Web Vitals Definitions, good thresholds and field assessment context for LCP, INP and CLS.