Website Performance Checklist: Core Web Vitals Before Launch

Speed is a trust signal before it's a ranking factor

A slow first load costs you visitors before Google's ranking algorithm ever gets a say — people leave a page that hasn't shown them anything useful within a couple of seconds, on principle, regardless of how good the product is once it loads. Core Web Vitals are Google's attempt to measure that exact experience with real numbers instead of a vague sense of “feels slow.”

The two metrics worth knowing by name

Largest Contentful Paint (LCP) measures how long it takes the biggest visible element — usually your hero image or headline — to render. Google's published “good” threshold is under 2.5 seconds. Cumulative Layout Shift (CLS) measures how much content jumps around as the page loads — an image that pushes text down after it finally loads, or a banner that appears above the fold and shoves everything else. Google's “good” threshold there is under 0.1. Both are things a Lighthouse audit measures directly rather than estimates.

Common mistakes we see

• Unoptimized hero images. A multi-megabyte PNG used as a full-width hero background, when a compressed, correctly sized WebP would look identical and load in a fraction of the time.
• Images or embeds with no reserved size. The browser doesn't know how tall an image will be until it finishes loading, so everything below it jumps down once it does — a direct CLS hit.
• Render-blocking fonts and scripts. Custom fonts or third-party scripts loaded in a way that delays everything else on the page from painting.
• Cookie banners and promo bars that inject late. They appear after the initial layout settles, shifting content that had already rendered — often the single biggest CLS contributor on a marketing site.

How to check it yourself

Run your page through Google's PageSpeed Insights (the same Lighthouse engine LaunchGraded uses) and look specifically at the LCP and CLS numbers, not just the overall score — a page can score reasonably overall while still failing one metric badly. Watching a real, throttled mobile load of your own page is also enough to catch the CLS problems by eye: anything that visibly jumps once it finishes loading is a layout-shift bug.