Insights / Speed

Why your site is slow on mobile data, and how to fix it

Devaltech · 6 min read

A site that opens instantly on office fibre can take eight seconds on 4G in a matatu. The gap is almost always the same four things: uncompressed images, fonts that block the first paint, scripts that do nothing until someone scrolls, and a server that thinks before it answers.

Start with images

Images are usually more than half the weight of a page. Serving them in a modern format, at the size they're actually displayed, and loading the ones below the fold only when they're needed, will do more for your load time than any other single change.

Then the fonts and the scripts

Custom fonts should swap in rather than hold the page blank. Third-party tags - chat widgets, heatmaps, extra analytics - each cost you something; keep the ones that earn their place and drop the rest.