What are Core Web Vitals?

Three metrics Google uses to measure page experience: Largest Contentful Paint for loading, Interaction to Next Paint for responsiveness, and Cumulative Layout Shift for visual stability. They are assessed on real visitor data over a rolling 28-day window.

How do I improve Largest Contentful Paint?

Find what is on the critical path before the largest element can paint, and remove it. Usually a render-blocking stylesheet, a late-discovered font, an oversized image, or a client-rendered page where nothing paints until a bundle executes.

Does page speed affect Google rankings?

Yes, but less than commonly claimed. Core Web Vitals are a real ranking input and behave more like a tie-breaker between otherwise comparable pages. The larger, more reliable effect of speed is on conversion — slow pages lose customers regardless of ranking.

Performance

Why is my website slow?

Usually one of four things: unoptimised images, render-blocking CSS or JavaScript, a slow server response, or a framework executing before anything paints. Measure first — the cause is almost never what people assume, and fixing the wrong one changes nothing.

Answered by Anas Bin Masud 206 words 3 sections

Diagnose in this order

Time to First Byte — if it is above 800ms, everything downstream is capped and the server is the problem
The LCP element — what is the largest thing on screen, and what must complete before it can paint?
Image transfer sizes on mobile — a 2000px image on a 390px screen is the most common single waste
Total JavaScript, parsed and executed before first paint
Third-party tags, which nobody has audited since installation

The fixes that usually pay most

Responsive images with srcset, in AVIF or WebP
Moving to a CDN, which can remove hundreds of milliseconds from every metric at once
Removing framework JavaScript from pages that do not need it
Enabling Brotli, if your host still serves gzip only

Lab versus field

Lighthouse simulates one load on one device. Field data is what real visitors experienced, and it is what search engines assess. When they disagree, believe the field data and use the lab tool to find the cause.

The longer version

This answer is deliberately short. If you want the full treatment, Core Web Vitals, and the order that actually reduces them covers it in about 3 minutes — free, ungated, written from client work.

Who answered this

Anas Bin Masud builds e-commerce sites and does technical SEO for businesses in the UK, Canada and Pakistan — fifteen live client sites, six of them stores taking real payments. These answers come from those projects rather than from a content brief. More about how I work, or ask me something directly.