Largest Contentful Paint
Reports the LCP timing observed during the current controlled Chromium page load.
Free LCP test
Check Largest Contentful Paint and find what is slowing it down.
Measure synthetic LCP in a controlled browser and inspect server response time, render-blocking resources, page weight and resources SiteState flags as LCP-critical.
Free · No signup required · Real Chromium lab test
What this tool measures
LCP plus the signals that help explain it
First Contentful Paint
Shows when the browser first paints text or image content before the largest content element appears.
Time to First Byte
Shows whether the main document response is already delaying the rendering timeline.
LCP-critical resources
Surfaces resources SiteState classifies as important to the main-content rendering path.
Render-blocking resources
Highlights CSS, scripts or other resources that can hold up initial rendering.
Page weight and JavaScript
Adds transfer size and browser CPU evidence when the delay continues after the server responds.
Interpret the result
Why is my LCP slow?
A slow LCP can come from different parts of the load path: server response, a large hero image, render-blocking styles, font loading, JavaScript or other dependencies. That is why a useful LCP checker needs more context than the final number.
SiteState's report keeps LCP next to TTFB, resource classifications and browser CPU so you can identify the next investigation instead of treating every slow LCP as the same problem.
Methodology
LCP is measured in a controlled desktop Chromium lab run. It is useful for repeatable debugging and regression testing, but it is not a replacement for real-user field LCP.
FAQ
Common questions about this speed test
What is Largest Contentful Paint?
Largest Contentful Paint is a loading metric that records when the largest visible content element in the viewport is rendered.
What can make LCP slow?
Common contributors include slow server response, heavy images, render-blocking CSS, delayed fonts, JavaScript work and resource dependencies. The SiteState report exposes several of these signals together.
What tool should I use to find out why LCP is slow for real users?
Use field data such as CrUX or your own real-user monitoring to confirm that real visitors have slow LCP, then use a controlled LCP test like SiteState to reproduce the page load and investigate TTFB, the LCP resource, render blockers, page weight and JavaScript.
Is this LCP test lab or field data?
It is synthetic lab data from a controlled browser run. Real-user field LCP can differ because actual visitors use different devices, networks and locations.
Can SiteState detect LCP regressions?
SiteState's synthetic monitoring can track compatible browser metrics over time and surface sustained performance regressions against recent baselines.
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