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Web vitals
07-28-2020, 07:25 AM
Post: #4
RE: Web vitals
Hi David,

As others have pointed out, Web Vitals is a set of metrics. This can be measured by the actual WPT Chrome agent itself or by submitting a test to Google LightHouse tool. When you enable this option, WPT actually runs both the tests.

Since the tests are different and run from different machines and network conditions, you should see minor difference in the numbers.

The only case where you would see a huge difference is when you run a multi-step test. In this case, WPT will simulate a browser going from page 1 to page 2. Due to the navigation, browser may have cached JS, CSS, fonts and images. So the metrics would show lower value indicating the behavior of a real user clicking on a link and going to second page. However, Google LightHouse does not have this capability. Each test would be single page test and this will give you a higher number.

Here's an example. I am using the following script to test 2 pages on I have hidden measurements on first page.

logData    0
logData    1

Here's the WPT link:

Here's Lighthouse report:

If you notice, there is a huge difference between the results. FCP is 1.312s vs 6.3s on Lighthouse. Similarly, LCP is 4.17s vs 17.4s on LightHouse.

Hope this helps address your question.


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Messages In This Thread
Web vitals - david.c - 07-01-2020, 01:06 AM
RE: Web vitals - isotropic - 07-16-2020, 05:57 AM
RE: Web vitals - Webnauts - 07-20-2020, 11:05 PM
RE: Web vitals - akshayranganath - 07-28-2020 07:25 AM

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