What actually makes a website fast
By The AsasWeb team 1 min read
The biggest single cause of slow websites is too much JavaScript, so the biggest gain is shipping less of it. After that, serve modern responsive images in formats such as AVIF and WebP with width and height set, and self-host, subset, and tune your web fonts. Measure Core Web Vitals on a mid-range phone and a slow connection, because speed comes from choices made throughout the build, not a patch at the end.
Everyone wants a fast website, and most advice stops at “optimise your images”. Images matter, but speed is the sum of many decisions made while building. Here is where the real gains are.
Ship less JavaScript
The single biggest cause of slow sites is too much JavaScript. Every kilobyte has to be downloaded, parsed, and run, often on a mid-range phone with far less power than a laptop. Send mostly HTML and CSS, and add JavaScript only where it genuinely earns its place. Pages that work without it are faster and more robust.
Serve modern, responsive images
Use modern formats such as AVIF and WebP, generate several sizes, and let the browser pick the right one for the screen. Always set width and height so the layout does not jump while images load. A phone should never download a desktop-sized image.
Self-host and tune your fonts
Web fonts are easy to get wrong. Self-host them, subset them to the characters you need,
use font-display: swap, and tune the fallback metrics so text does not shift when the web
font arrives. That protects your Cumulative Layout Shift score.
Measure what users feel
Core Web Vitals describe the real experience: Largest Contentful Paint for loading, Cumulative Layout Shift for stability, and Interaction to Next Paint for responsiveness. Measure them on a representative mid-range phone and a slow connection, not just on a fast laptop, because that is what many of your visitors are using.
Performance is built in, not bolted on
You cannot sprinkle speed on at the end. It comes from the choices made throughout the build, which is exactly how we approach every project. If your site feels slow, start a project and we will find out why.