Core Web Vitals in practice
What LCP, INP and CLS measure, why lab scores and field data disagree, and where WordPress sites fail. Sessions at TDC Business 2023 and the Abradi webinar.
Core Web Vitals in practice is my talk about the three metrics Google uses to judge page experience on real visits: LCP, INP and CLS. I explain what each one measures, why lab scores and field data disagree, and where WordPress sites usually fail. I have given it in Portuguese at Brazilian events under different titles, most recently at TDC Business 2023, and discussed the same subject on podcasts. This page lists every version, with the official event page or the recording for each.
Where I gave this talk
| Date | Event | Session | Link |
|---|---|---|---|
| September 19, 2023 | TDC Business 2023, Web and Front-end track | Impulsionando a Velocidade e Experiência: Desvendando os Core Web Vitals | Track page |
| June 27, 2023 | Abradi webinar (online) | Melhore a Experiência do Usuário com Core Web Vitals | Recording |
I also talked about Core Web Vitals on two podcasts, both recorded:
- Performance, WordPress & Google Core Web Vitals, Martincast #102 with John Martin, May 16, 2023.
- Core Web Vitals WordPress, with Seo Martin, August 4, 2021.
What the talk covers
The talk starts with the definitions, because most confusion about Core Web Vitals comes from mixing up the metrics and the tools. Google assesses each metric at the 75th percentile of field data from real Chrome users, collected in the Chrome UX Report over a rolling 28-day window.
| Metric | What it measures | Good | Poor |
|---|---|---|---|
| LCP | When the largest image or text block in the viewport renders | 2.5 s or less | Over 4 s |
| INP | The delay between an interaction and the next frame on screen | 200 ms or less | Over 500 ms |
| CLS | How much visible content moves without the user causing it | 0.1 or less | Over 0.25 |
INP replaced First Input Delay as a Core Web Vital in March 2024, after the 2023 sessions listed above. The material on this page uses INP.
From there, the talk moves to practice:
- Why a green Lighthouse score does not change the field data Google uses, and how to read both in PageSpeed Insights.
- How to find which template and which metric fail, using the Core Web Vitals report in Search Console.
- The usual WordPress causes: slow server response without a page cache, a lazy-loaded hero image, render-blocking theme and plugin assets, third-party scripts and layout shifts from fonts, ads and embeds.
- The order I fix things in, starting with what affects every page.
Who it is for
Site owners, marketing teams and developers who see a failed Core Web Vitals assessment and do not know where to start. No coding is needed to follow the first half. The second half shows the WordPress fixes at a level a developer can take straight to a ticket.
Related articles and guides
The written version of this material is in Core Web Vitals for WordPress: the complete guide. For the basics, start with what Core Web Vitals are, and for each metric see LCP in WordPress, INP in WordPress and CLS in WordPress. If you need someone to look at your own site, see my Core Web Vitals consulting. The rest of my sessions are on the talks page.