Introduction to Core Web Vitals

Identify issues with core web vitals in real time and improve SEO.

Use Marfeel’s core web vitals module to track the performance of your site in the areas that most affect Google rankings, including LCP, CLS, FID, and more. Use this module to prioritize the most damaging issues impacting your score.

Never lag behind: access core web vitals data in real time without waiting for an updated CrUX report. Marfeel bases core web vitals data on real user sessions as opposed to synthetic traffic or server simulations. All user pageviews are tracked using the Performance Observer API.

Core web vitals insights are located under Site Technology → Web Vitals.

Largest Contentful Paint (LCP)

The time it takes for a page’s largest image or text block to render relative to when the page first loads. A good LCP score is under 2.5 seconds.


Cumulative Layout Shift (CLS)

Layout shifts are reported when an element that is visible within the viewport changes its start position between two frames. A good CLS score is less than 0.1.


First Input Delay (FID)

The time between when a user attempts to interact with a page, for example, by clicking a link, and when the browser starts processing event handlers in response to the request. A good FID score is under 100 ms.


Time To First Byte (TTFB)

The time between the request for a resource and when the first byte of a response begins to arrive. Although not considered a core web vital, it is a foundational metric that precedes every other loading metric for navigation requests, including LCP. A good TTFB score is under 800 ms.


DOM content loaded

The DOM (Document Object Model) defines the logical structure of documents, and the DOMContentLoaded fires when all the nodes in the page have been constructed in the DOM tree without waiting for images and CSS to finish loading.

It’s a useful event in terms of the speed of your page because there’s less to load before the event fires. For SEO purposes, note that Google does not consider this a reliable metric for page performance.

Onload events

When an object has been loaded. Onload is most often used within the element to execute a script once a web page has completely loaded all content such as images and iframe.

Further reading:
  • Insights: All about Marfeel’s Core Web Vitals module including filtering capabilities and the CWV Offenders feature

  • Easy Improvements: Learn how to optimize LCP and CLS with a couple of simple fixes