Slow websites lose clients: what PageSpeed is and how to reach 100
People opening your website on their phone, over a mobile connection, don't wait. PageSpeed Insights shows how much that wait costs, and it can almost always be fixed.
What PageSpeed Insights is
PageSpeed Insights is a free Google tool: you paste in a website's address and get scores from 0 to 100 in four areas: performance, accessibility, best practices and SEO. The performance score simulates a mid-range phone on a slow connection, on purpose: that is the situation of many of the people who will visit your website.
Below the scores, the tool lists what is slowing the page down. It's a good starting point, even if you're not technical.
Core Web Vitals
Besides the lab score, Google tracks three measures of the real experience of visitors, called Core Web Vitals:
- LCP (Largest Contentful Paint): how long the page's main content takes to appear. Good is up to 2.5 seconds.
- INP (Interaction to Next Paint): how long the page takes to react to a tap or click. Good is up to 200 milliseconds.
- CLS (Cumulative Layout Shift): how much the page "jumps" while loading, like when you go to tap a button and it moves. Good is up to 0.1.
This data comes from real visitors using Chrome and only appears once the website has enough traffic. It is one of the signals Google uses to rank results. It isn't the main factor (content still comes first), but between two similar pages, the faster one has the edge.
Why speed turns into clients
Every second of blank screen is a chance for the person to go back to the search results and click on a competitor. And people who give up don't show up anywhere: you never even find out you lost the lead. A fast website doesn't guarantee the sale, but it does make sure the person gets to read what you have to offer.
What usually makes a website slow
- Heavy images: photos uploaded straight from a camera or phone, several megabytes each, to fill a small space.
- Too many scripts: chat widgets, ad pixels, carousels, pop-ups and plugins that load code even when they aren't used.
- Visual builders and ready-made themes: they tend to ship a lot of code to cover every case, including the ones your website doesn't use.
- Too many fonts: every font family and weight is one more file to download.
- Slow hosting: a server that takes a while to respond delays everything that comes after it.
How to get close to 100
- Resize images to the size they are displayed at and use modern formats such as WebP or AVIF.
- Set image width and height and reserve space for anything that loads later. That fixes most of the CLS.
- Cut what doesn't bring in clients: every third-party script has to justify its weight.
- Prefer system fonts, or at most one font family hosted on the website itself.
- Host on a service with a CDN, which delivers files from a server close to the visitor, and configure caching.
- Measure again after every change. The score varies a little between runs; what matters is the trend.
This website is the example
This blog and the Authentic Development website are built with plain HTML and CSS, no JavaScript, using the device's own fonts and hosting with a CDN. The result is 100 on all four PageSpeed scores on mobile. You can check it right now: paste this page's address into the tool.
Not every website needs to be this lean. An online store or a booking system needs more features. But the rule applies to all of them: everything that goes on the page has to be worth the time it costs the person waiting.