Understanding Core Web Vitals

Core Web Vitals are three user-experience metrics: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness and Cumulative Layout Shift for visual stability. They describe important parts of experience, not the complete quality of a website.

Know the current good thresholds

At the time of this article, web.dev defines good values as LCP at or below 2.5 seconds, INP at or below 200 milliseconds and CLS at or below 0.1. Assessment uses the 75th percentile of visits. Review the linked primary documentation when using these thresholds in an audit because standards and tools can evolve.

Separate field data from lab diagnosis

Field data reflects real users, devices and networks. A controlled lab run helps reproduce and diagnose a problem but is not interchangeable with a site's field assessment. Small or new pages may not have sufficient field data. Record the evidence available rather than assigning an unsupported pass.

Investigate each metric differently

These are investigation directions, not a guarantee that one optimisation fixes every poor score. Use a trace or diagnostic tool to identify the actual cause.

Check the complete task

A stable, fast page can still have unreadable copy or a broken form. After performance changes, complete the contact or booking journey again. Preserve accessibility, useful content and clear feedback. Do not substitute a high score for a successful customer action.

Make measurement repeatable

Record page, device conditions, tool, date and changes made. Compare equivalent tests and watch field data over time. Core Web Vitals can inform search and user experience work, but meeting thresholds does not guarantee ranking or sales. Website speed and business performance explains how to connect technical evidence with business outcomes responsibly.