Core Web Vitals describe loading, responsiveness and visual stability. Use them to prioritise visitor problems, alongside enquiries and usability.
Understand the three measurements
LCP measures when the largest visible content appears. INP measures interaction responsiveness. CLS measures unexpected layout movement. A page may load its main image quickly but still respond poorly when someone opens a menu or submits a form.
Separate field and laboratory evidence
Field data reflects eligible real visits over time. Laboratory tests provide repeatable diagnostics under selected conditions. A new page may lack field data; test it locally, monitor actual visitors where permitted, and avoid treating one score as a complete assessment.
Choose work by visitor impact
Start with common templates and important enquiry journeys. Record the affected device, page and interaction, then compare before and after under similar conditions. Keep conversion tracking separate: better performance can support usability but does not guarantee more sales.