Largest Contentful Paint (LCP) is a measurement of how long the largest element on the page takes to render. It’s one of several Web Vital metrics that measure how real users perceive the performance of modern web applications. New measurements like Largest Contentful Paint are increasingly important as JavaScript and SPA’s render more content after page load is completed.

Cumulative Layout Shift (CLS), sometimes known as jank, is a measurement of how much elements move due to late-rendered content. You can think of it as a measurement of layout instability. It has become a common problem for many websites due to third-party scripts and tag management and its one of the new Core Web Vital metrics.

How is Google so fast? It’s so fast we take it for granted. It feels instant from the time you search to when results are displayed. What can we learn about the techniques they use to make their site so fast?

This is the complete guide to the metrics, methods, and measurements of web performance in 2023. If you run a website, this guide has all the fundamental ideas you need to understand to build a fast website for your users, and for search engines.