Preview
What it is.
Paste a URL and you get two answers: what Chrome users met over the previous 28-day collection period, and what a Lighthouse run says in a controlled environment you can repeat after every deploy.
Google publishes the thresholds, so you can check the verdict instead of trusting it. Largest Contentful Paint counts as good up to 2500ms, Cumulative Layout Shift up to 0.1, Interaction to Next Paint up to 200ms, each read at the 75th percentile of visits.
What you get.
- A pass or fail on each Core Web Vital, measured on visits and not on a lab guess.
- The share of visits that landed in the poor band, so you know who it affected.
- The render-blocking files named, which is what makes the engineering ticket writable.
- A rerunnable lab test, so you can show a change worked before field data catches up.
How to set it up.
Paste the URL and read the field data first, since the lab score is a simulation and the field data is what visitors met.
Switch between Mobile and Desktop, and treat the mobile numbers as the ones that count.
Compare each metric against the published thresholds: 2500ms for Largest Contentful Paint, 0.1 for Cumulative Layout Shift, 200ms for Interaction to Next Paint.
Open the diagnostics and work the render-blocking resources and image sizing items before anything else.
Rerun the lab test after each change, and wait for the 28-day window to catch up before you judge the field data.
Pricing Plans
Web interface
$0
no login, with separate mobile and desktop reports
Use cases
Settle the speed argument
Run the page, screenshot the field verdict, and put a published threshold next to the complaint.
Render-blocking list
Take the files delaying first paint to whoever owns the head of the page.
Before and after
Test the page before a change and again afterwards, so the improvement carries a number.
Best for
Settling a speed argument
Field data from Chrome visits ends the debate about whether a page is slow for users or only slow on someone's laptop.
Checking a landing page before launch
The lab run works on a page with no traffic yet, which is exactly when field data has nothing to show.
Prioritising engineering work
The diagnostics list names the files, so a ticket can carry the filename instead of the word slow.
Open the tool
Opens on Google in a new tab.