Review the key Core Web Vitals metrics and understand what they measure. Browser-session measurements can offer limited diagnostic clues, while a reliable assessment may require lab testing and real-user field data.

What this tool can do

• Largest Contentful Paint (LCP): understand how quickly the main content loads.
• Interaction to Next Paint (INP): learn how responsive a page feels to user interactions.
• Cumulative Layout Shift (CLS): review unexpected visual movement during page use.
• Measurement context: distinguish limited local metrics from complete field or lab reports.

How to use the core web vitals checker

1. Open the page you want to assess and start the measurement.
2. Interact with the page if you are evaluating responsiveness.
3. Review any available browser-session measurements and the notes explaining their limits.
4. Run a dedicated lab test and review real-user field data when available.
5. Address the largest issues and retest under comparable conditions.

Important notes

• LCP, INP, and CLS vary by device, network, content, and interaction.
• A single browser session is not a substitute for representative real-user field data.
• Do not interpret missing metrics as a passing result; the page may not have generated enough measurement data.

Frequently asked questions

What are Core Web Vitals?

They are user-experience metrics focused on loading performance, responsiveness, and visual stability.

What does LCP measure?

LCP measures when the largest visible content element is rendered in the viewport.

What does INP measure?

INP assesses interaction responsiveness across a page visit, based on observed interactions.

What does CLS measure?

CLS measures unexpected layout shifts that occur during a page’s lifetime.

Why do field and lab results differ?

Lab tests use a controlled environment, while field data reflects a wider range of real devices, networks, and user behavior.

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