While working on client websites, I kept encountering the same issue. Whenever you change a theme, add a plugin, or modify cache settings, the "field data" in Google Search Console or PageSpeed ​​Insights takes weeks to update - this is because it is based on a 28-day rolling average. For smaller websites, this data is often unavailable altogether.

That is why I created the "CartHacker Core Web Vitals Monitoring" tool.

It measures LCP, INP, and CLS metrics during every real user visit and, following Google’s methodology (where 75% of visits must meet specific thresholds), indicates within your WordPress dashboard whether your site meets the requirements. Results are available from the very first visit. A daily chart allows you to pinpoint exactly when a site’s performance began to decline; the chart also displays the TTFB (Time to First Byte) metric. The tool works on any WordPress-based site, not just online stores.

Key principles I followed while developing this solution:

• The measurement script is served from your own website and loaded in a "deferred" mode, ensuring it does not slow down page loading.
• No cookies are used; no data is stored on the user's device, no need to update your cookie banner.
• Activity from logged-in administrators, editors, and authors is excluded from the statistics, so your own clicks do not skew the results.
• For the CLS (Cumulative Layout Shift) metric, the tool identifies the element that shifted the most: for example, a cookie banner or a section displaying related products.
• The tool also tracks traffic (page views, unique users, devices, browsers) without the use of cookies.
• The source code for every file is fully readable and requires no additional build step. The measurement script is located in `assets/js/ch-monitor.js`, and the `readme` file lists all the requests it sends.

Using the tool requires a free CartHacker account, as data is stored and processed on the carthacker.com platform. The free plan includes up to 1,000 page views per day, a 7-day data history, weekly email reports (when agreed), and performance drop notifications. Paid plans offer longer data retention and higher page view limits.

You can try it for free here:
https://wordpress.org/plugins/carthacker-core-web-vitals-monitoring/

I would appreciate any feedback - especially if you notice discrepancies between the results provided by my tool and those you see in PageSpeed ​​Insights or Google Search Console.