The three numbers
- LCP (Largest Contentful Paint). When the main thing on the page — usually a hero image or heading block — appears. Heavy images, slow hosting and render-blocking scripts are the usual culprits.
- INP (Interaction to Next Paint). How quickly the page reacts after a click or tap. Bloated JavaScript is the usual culprit.
- CLS (Cumulative Layout Shift). How much the page jumps as things load. Images without size, ads and late webfonts are the usual culprits.
Lab scores in Lighthouse are a hint. Field data — what real users on real phones saw — is what Google uses. Search Console’s Core Web Vitals report is the one that matters.
What is worth doing
Compress and size images. Do not ship three slider libraries for one banner. Reserve space for media so the page does not jump. Host close to users. Fix the worst URLs first; a site-wide rewrite for a 0.05 improvement on an already-green page is theatre.
This work belongs on public websites, not as a reason to stall an internal tool. If you want it done as part of a build, it is in the web development service, not a separate “SEO package” bolted on after launch.