Core Web Vitals

Web Vitals is an initiative by Google to provide a standard set of metrics that web site owners can use to evaluate the quality of the experiences their web sites are delivering to users. The Core Web Vitals (CWV) are a subset of these metrics that apply to all websites and are considered essential to user experience. They are used as key ranking factors for search engine optimization, so in addition to providing a superior user experience, improving a site’s performance against the Core Web Vitals can help it rank higher in search results and garner more traffic.

Catchpoint’s Web, WebPageTest, and Transaction tests, as well as Real User Monitoring (see limitations at the bottom of this article), capture Core Web Vitals metrics so that you can see how your site is performing against this key industry benchmark.

Core Web Vitals Metrics

The Core Web Vitals metrics include: Largest Contentful Paint, Cumulative Layout Shift, and Interaction to Next Paint.

• Largest Contentful Paint (LCP) – A measure of initial loading time, this metric captures how long it took for the largest single image or text element (in terms of screen area) to be displayed on the visible part of the screen. For a quality user experience, LCP should be less than 2.5 seconds. If LCP is between 2.5-4 seconds it needs improvement, and an LCP above 4 seconds is considered poor.

• Cumulative Layout Shift (CLS) - Indicates the page’s visual stability. This metric identifies links or buttons that shift their location on the screen after the page has loaded. This reflects the level of difficulty users may experience when trying to interact with the page. CLS should be maintained at 0.1 or less. Anything between 0.1-0.25 needs improvement, and anything above .25 is considered poor.

• Interaction to Next Paint (INP) - Measures the responsiveness of a webpage across all user interactions during a session. An interaction happens with a visitor of the website clicks, taps, or presses an element on that page, producing a change of presentation on the screen. INP measures the time between the user’s action and the new presentation. An INP below 200ms represents good responsiveness, 200-500ms indicates that page needs improvement, if the INP is above 500ms, the page responsiveness is poor.

Additional Web Vitals

Although not considered Core Web Vitals, the following metrics are also available and supported by Catchpoint (with the limitations for RUM cited below.)

• First Contentful Paint (FCP) - Measures the time from when the user first navigated to the page to when any part of the page's content (is rendered on the screen.
• Time to First Byte (TTFB) - Measures the time between the request for a resource and when the first byte of a response begins to arrive.

RUM Limitations

Web Vitals are captured by the browser, and not all browsers support all Web Vitals. RUM can only report Web Vitals that are supported by the end-user's browser. This limitation would apply to any tool that measures and reports Web Vitals.