User experience metrics
Core Web Vitals Checker
Check LCP, INP, CLS, FCP, and TTFB when PageSpeed Insights is configured, with a fallback readiness audit when field data is unavailable.
Tool guide
What is the Core Web Vitals Checker?
The Core Web Vitals Checker focuses on three user-experience metrics: Largest Contentful Paint (LCP), Interaction to Next Paint (INP), and Cumulative Layout Shift (CLS). When PageSpeed Insights data is available, the tool reports eligible field or Lighthouse values and classifies them against commonly used good, needs-improvement, and poor ranges.
Core Web Vitals are measured in a rendered browser, not from static HTML alone. For that reason, the page never invents LCP, INP, or CLS values. When the Google API is not configured or a URL has insufficient field data, the tool explains the limitation and provides supporting technical checks instead.
Audit coverage
What this SEO tool checks
LCP as a loading-experience signal
INP as a responsiveness signal
CLS as a visual-stability signal
Supporting FCP, server response, and resource information
Availability of field data versus lab data
Step-by-step
How to use the Core Web Vitals Checker
- 1Enter the exact page URL
Different templates and content can produce different vitals, so test representative pages.
- 2Select the device strategy
Run mobile first and repeat on desktop where relevant.
- 3Analyze the available data
The report distinguishes actual PageSpeed metrics from fallback readiness checks.
- 4Investigate the cause
Use browser performance tools to connect a poor metric with the responsible image, script, layout, or server delay.
Interpretation
How to understand the results
- Good LCP is generally 2.5 seconds or less; values above 4 seconds are commonly treated as poor.
- Good INP is generally 200 milliseconds or less; values above 500 milliseconds are commonly treated as poor.
- Good CLS is generally 0.1 or less; values above 0.25 are commonly treated as poor.
Practical advice
SEO best practices
- Preload or prioritize the true LCP image or critical content without overusing preload.
- Reserve width and height for images, ads, embeds, and dynamic components.
- Break long JavaScript tasks into smaller work and reduce unnecessary third-party code.
- Improve server response and cache HTML where appropriate.
- Track the 75th percentile in field data instead of relying only on one lab run.
Before you act
Limitations of this automated check
Field data may be unavailable for low-traffic pages and can be reported at origin level instead of URL level. Lab tests are controlled simulations and may not match real users. The tool cannot diagnose every cause from summary metrics; detailed browser traces and real-user monitoring are still needed.
Deeper explanation
Understand the decision behind the check
Use the practical guide below when you need context, common mistakes and a verification workflow instead of only a pass/fail result.
Common questions
Core Web Vitals Checker FAQs
What is the difference between field and lab data?
Field data comes from eligible real-user experiences over time. Lab data is a controlled test useful for debugging and repeatable comparisons.
Why is INP unavailable?
The URL may lack sufficient field data, the API response may omit the metric, or the test may not include real interaction data.
Can static HTML reveal CLS?
It can reveal risks such as images without dimensions, but actual CLS requires observing the rendered page as elements load and move.
How quickly do field metrics update?
Field datasets use rolling historical windows, so improvements may take time to appear after deployment.
Continue your audit