Core Web Vitals are a subset of Web Vitals, a set of "quality signals that are essential to delivering a great user experience on the web" that are part of a Google initiative for better user experience. They provide qualitative measures of user experience on a page, and as of summer 2021 are officially taken into account in Google's ranking algorithms.

The three Core Web Vitals are:

  • Largest Contentful Paint (LCP): measures loading performance (speed).

  • First Input Delay (FID): measures interactivity, particularly the delay before a page can process user activity like clicks and scrolls.

  • Cumulative Layout Shift (CLS): measures visual stability through how much elements move around the page during loading.

These metrics are measured through anonymized user data from consenting Chrome users as part of the CrUX report, aggregated over a period of the past 28 days. Data collected in this way is called field data.

When measured at a given instant through approved tools, the data collected is called lab data. In this case, the FID is replaced with Total Blocking Time (TBT), which measures time to interactivity.

Data on Core Web Vitals in Oncrawl

Data on Core Web Vitals in Oncrawl is available in the crawl analysis dashboards where it is aggregated per page group and across the entire site.

It is also presented in the Data Explorer, and in the URL details, where the data for each URL is available.

Oncrawl collects and analyzes the following data:

  • FCP - First Contentful Paint

  • CLS - Cumulative Layout Shift

  • LCP - Largest Contentful Paint

  • TTI - Time To Interaction

  • Speed Index

  • TBT - Total blocking time (Lab data equivalent of FID)

  • Performance Score

Enabling Core Web Vitals in Oncrawl

To analyze Core Web Vitals, the analysis needs to be included in your crawl:

  1. Your plan must include the JavaScript+Core Web Vitals option. Please contact us via the chat to enable it if this is not already the case. This option is free.

  2. Click on Set up a crawl

  3. Click on Show extra settings

  4. Expand the Crawl JS settings

  5. Enable both JavaScript and Core Web Vitals

  6. Launch the crawl

Analyzing Core Web Vitals in Oncrawl

Oncrawl provides two dashboards on Core Web Vitals.

Core Web Vitals in the Crawl Report

Access the Core Web Vitals report under Crawl Report > Performance > Core Web Vitals.

This report contains:

  • Information about site-wide performance on all of the metrics Oncrawl tracks

  • Information about site-wide performance on Core Web Vitals metrics

  • Breakdown of performance on each Core Web Vitals metric by page group for any segmentation

  • Information on potential gains from optimization of Core Web Vitals

Optimizations are the sum of savings calculated by Lighthouse for the recommended improvements for each page in the crawl. Since these optimizations vary from page to page, and are not always feasible, they are not included in the data. However, they provide a meaningful, quantitative measure of the impact of changes on a given page.

You can use optimization savings reported in Oncrawl to prioritize or estimate the pertience of possible Core Web Vitals improvements. If you need specific details, you can run a Lighthouse audit for the URL in question.

Core Web Vitals in the SEO Impact Report (cross-analysis)

Oncrawl offers blended analysis between Core Web Vitals and log files or analytics data (Adobe Analytics, Google Analytics, AT Internet...).

Access the Core Web Vitals cross-analysis report under SEO Impact Report > Performance > Core Web Vitals.

This report contains information about the relationship between behavior on your site and Core Web Vitals scores:

  • Based on number of organic visits per pages

  • Based on whether pages receive organic traffic

  • Based on whether pages are crawled by search engine bots or not

  • Based on how frequently search engine bots crawl your pages

Why measure Core Web Vitals using lab data?

The data in Oncrawl for Core Web Vitals is based on Lab data, which is measured each time an analysis is performed. While this can create variations in the data, since each time lab data is measured, the context is slightly different, lab data also has several advantages over field data:

  • Oncrawl can provide data for every single URL in an analysis

  • Oncrawl's solution allows you to analyze Core Web Vitals in contexts in which field data can't or shouldn't be available: staging websites, newly created URLs, and newly updated URLs...

  • Oncrawl doesn't need to wait for Google to have sufficient data (28 days) for a specific URL

This means that, in accordance with web.dev recommendations, Oncrawl reports on TBT (Total Blocking Time) instead of FID (First Input Delay). Optimisations that affect TBT have the same effect on FID.

Web.dev recommendations for measuring FID when working with Lab data

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