PageSpeed Insights Library

What is the avoid excessive-DOM size warning in lighthouse, PageInsights etc? Lighthouse flags pages that have either: more than 1,500 DOM nodes in total.This means that there…

How to avoid enormous network payloads? The optimizations below should be an integral part of your development workflo, ensuring you are providing a fast-loading page…

How do Layout Shifts affect page performance? When a user visits your webpage, they’re usually looking to quickly interact with buttons, contact forms, images and…

Overview Deferring offscreen images (or lazy-loading) refers to the practice of delaying the loading of images that aren’t in your visitors’ viewport until they are…

Overview Browsers like Chrome normally block page scrolling during the initial page load until JavaScript has executed. With JavaScript already blocking the main-thread, smooth scrolling is…

Overview Images and videos likely account for the bulk of your total page size compared to HTML, CSS, or JavaScript files. If these images are…

Overview Render-blocking resources are scripts, stylesheets, and HTML imports that block or delay the browser from rendering page content to the screen. These resources delay…

Lighthouse: Enable text compression Overview Enabling text compression allows you to serve smaller text-based resources like HTML, CSS, and JavaScript in the interest of faster…

Overview Images and/or videos that do not have explicit width and height attributes can cause large layout shifts as your page loads. Layout shifts can be frustrating to your page visitors…

Overview Cumulative Layout Shift (CLS) is a performance metric used to measure the perceived page load visual stability or the unexpected shifting of web elements while loading…

Overview Speed Index (SI) is a metric that measures how fast your page is visually complete above-the-fold (what you can see without scrolling). SI is…

Overview Time to Interactive (TTI) is a metric that measures a page’s load responsiveness and identifies situations where a page looks interactive but actually isn’t. TTI…

Total Blocking Time (TBT) is a new Lighthouse Performance metric that quantifies your page’s load responsiveness to user input. It measures the total amount of…

Overview Largest Contentful Paint (LCP) is a performance metric that measures the perceived loading experience for users. Simply, LCP measures how long it takes for…

Overview Minifying CSS files can help reduce their file sizes by removing comments, white spaces, and redundant code. The smaller the CSS files are, the faster they are downloaded…

Overview Minifying JavaScript files is an optimization technique to reduce JavaScript payload and the main-thread blocking time. Minification can help reduce JavaScript file sizes by removing comments, white…

Overview ‘Minimizing main-thread work’ is a high impact audit within the context of your site performance. The main-thread handles most of the processes involved in loading your…

Preloading the Largest Contentful Paint (LCP) image can display your hero image much earlier in the page load. A fast LCP enables your page visitors…

Time to First Byte (TTFB), also known as server response time, is the time it takes for the browser to receive the first byte in response…

Overview Reducing JavaScript execution time, in general, refers to decreasing the amount of time spent parsing, compiling, and executing JavaScript files. By default, JavaScript executes on the main-thread and when this…

Overview Third-party code consists of analytics services, advertisements and other elements that are served from an external domain URL. These resources are often responsible for…

Overview Most websites serve images in JPEG or PNG formats, these formats have been around for over 20 years! The availability of a new generation…

Overview Serving static assets with an efficient cache policy helps improve page load times on repeat visits by storing these files locally in the user’s…