Core Web Vitals (CWV) are a set of metrics developed by Google to measure the user experience of site visitors.
They give an idea of how a web page is performing and help identify areas that need improvement.
Google offers several metrics for measuring page performance called Web Vitals, which are different from Core Web Vitals. Web Vitals provides a granular technical view of web page performance.
Core Web Vitals are a subset of Web Vitals that measure common user experience interactions for site visitors, regardless of the type of site they visit.
Specifically, Google identifies key user experience needs as Loading, interactivityand visual stability.
All websites should strive for high Core Web Vitals scores.
According to Google:
“Web Vitals is an initiative by Google to provide unified guidance for quality signals that are essential for delivering an exceptional user experience on the web.
Site owners shouldn’t have to be performance gurus to understand the quality of experience they’re delivering to their users.
The Web Vitals initiative aims to simplify the landscape and help sites focus on the metrics that matter most, Basic Web Vitals.”
Measuring User Experience with Core Web Vitals
The following three metrics measure the quality of user experience for site visitors:
- The largest content painting: measures the perceived loading speed of the page and represents the time it takes to load the largest block of content (text or image).
- First Entry Delay: measures the delay between when a site visitor first interacts with the page and when the browser can respond to the interaction
- Cumulative layout change: measures the stability of a web page during its download, offering feedback on the degree of change in the layout.
Google explains why these three metrics, in particular, are so important:
“Google believes Core Web Vitals are essential to all web experiences.
Consequently, it undertakes to make these measures appear in all its popular tools. »
Related: Googler explains usability and user experience ranking factors
Two Basic Types of Web Vitals Metrics
Google offers two types of Core Web Vitals metrics: field data and lab data.
Terrain data is Core Web Vitals measurements taken by site visitors to web pages. The measurements occur among site visitors using a Chrome browser who have chosen to send their anonymized user experience data to Google.
User experience data creates the Chrome User Experience Report (CrUX).
It does not include page-level data until it reaches at least 1,000 monthly visits to that page.
You can find the field data collected as part of the Chrome User Experience Report using Google’s PageSpeed Insights tool.
Search Console also displays field data, reported in a way that makes it easy to view URLs aggregated by the three Core Web Vitals metrics.
The Data Studio CrUX dashboard visualizes CrUX data (more info here).
Lab data consists of simulated Core Web Vitals scores.
The purpose of the reports generated by Lab Data is to receive diagnostic information to improve web page speed scores.
Because there is a slight deviation each time a test is run, many people will run at least three tests and then average the score.
Core Web Vitals Lab data scores are also available through the PageSpeed Insights tool, as well as any other third-party tool that uses the Chrome Lighthouse tool.
A headless Chrome bot is sent to a web page to download and simulate data.
The Lighthouse tool applies artificial throttling to simulate a mobile device downloading the web page over a mobile phone connection.
Here’s how lab data simulation works:
“These exact numbers are defined in Lighthouse constants and used as Lighthouse’s default throttling.
They represent approximately the bottom 25% of 4G connections and the top 25% of 3G connections (in Lighthouse this configuration is currently called “Slow 4G” but was previously labeled “Fast 3G”).
This preset is identical to WebPageTest’s “Mobile 3G – Fast” preset and, due to lower latency, slightly faster for some pages than WebPageTest’s “4G” preset.
There are four types of simulated network throttling for those interested in the details of throttling.
1. Simulated strangulation. This is what is used by the Lighthouse tool.
2. Choke applied. This is called request-level throttling, but it’s called enforced throttling in the Chrome Developer Tools. According to the documentation, this limitation is not as precise, so the Lighthouse algorithm compensates for this.
3. Limitation at proxy level. This does not affect UDP and is therefore not ideal.
4. Packet Level Limitation. This is the most precise form of throttling, but it can also lead to more discrepancies between tests. Third-party webpage testing uses this form of throttling.
How to Measure Basic Web Vitals
As mentioned, Field Data is Core Web Vitals metrics collected from site visitors.
Google Search Console offers data from the Chrome User Experience Report (CrUX).
PageSpeed Insights also provides CrUX field data.
PageSpeed Insights and Chrome Dev Tools (under the Audit panel) offer simulated Core Web Vitals lab data.
Third-party measurement tools that use Chrome Lighthouse also provide Core Web Vitals Lab data.
A partial list of free and mostly free third-party speed test tools:
Related: Making SEO and User Experience Work Together
What about other page speed user experience metrics?
As crucial as the Core Web Vitals are, they are not the only user experience metrics to analyze.
An extended set of metrics called Web Vitals are available through tools like PageSpeed Insights.
Google recently announced a new metric called Interaction to Next Paint.
Interaction with Next Paint is a metric that measures the time it takes to interact with the entire web page, which Google refers to with the phrase, overall interaction latency.
Source: Chromium Blog
Feature image: Myroslava Gerber/Shutterstock