Why is my website slow? The 5 causes, explained for beginners

A page that takes four seconds to display loses half of its mobile visitors before it has shown anything at all. The good news: a slow website almost always comes down to the same five causes, and none of them requires a technician to understand. Here is how to recognise them, in order of frequency.

First, measure rather than guess

Your website feels fast to you because your browser keeps a copy of it in memory, and because you're on fibre. Your visitors, on the other hand, arrive for the first time, on 4G, in the street. Test the way they experience it: open PageSpeed Insights (free, by Google), paste your address, and look at the mobile score. Below 50, there's a problem; above 90, there isn't.

Cause #1: images that are too heavy

This is by far the most common cause. A photo taken on a phone weighs 3 to 6 MB; displayed at 800 pixels wide on the page, it would only need 100 KB, that is 50 times less. Five photos dropped in as is, and the page weighs more than a short film. The visitor on 4G waits, the screen stays blank.

The remedy: resize each image to the size at which it will be displayed, compress it (the WebP or AVIF formats halve the weight again), and only load the ones visible on screen, the rest as the visitor scrolls.

Cause #2: too many scripts from elsewhere

A share button, a live chat, an embedded video, three analytics tools, a fancy font: each one is a file to fetch from another server, and several of them block rendering until they have arrived. A brochure website loading thirty external scripts is common, and it's absurd. Every addition should be justified by real use.

Cause #3: the page is built on every visit

A CMS-based website (WordPress and the like) doesn't store pages, but pieces in a database. For each visitor, the server assembles the page: it launches a program, queries the database, runs every installed plugin, then sends the result. With ten plugins and a heavy theme, this build takes one to two seconds before the first byte is even sent. A static website, where the page already exists as a file, has no such delay.

Cause #4: shared, saturated hosting

On shared hosting at a few pounds or dollars a month, your website shares a machine with hundreds of others. When one of them is attacked or gets a traffic spike, they all slow down. There's nothing you can do about it, and you can't see it: the website is slow “sometimes”, for no apparent reason. Web hosting explained simply details the difference between shared and dedicated.

Cause #5: a server on the other side of the world

Every exchange between the browser and the server makes a physical round trip. To a server in Paris, it takes around ten milliseconds; to a server in the United States, around a hundred — and a page needs dozens of them. For European visitors, a server in Europe is the only right answer. A page's journey in 5 steps shows where this distance comes into play.

What Leopar does for you

All five causes are dealt with at the source. Photos are served at the size actually needed, not as originals. The page carries no superfluous external scripts: no trackers, no plugins. The website is static: a ready-made file, served as is, with no database and no on-the-fly building. It is hosted on a server in Europe, over HTTPS, and not on a machine shared with hundreds of strangers.

That's also why a Leopar website settles for one well-built page rather than ten average ones: for a shop or a freelancer, a fast page that says everything converts better than a sprawling website that crawls. Building your website yourself or with Leopar compares the two approaches.

Frequently asked questions

What is a good loading time?
Under 2 seconds on mobile to see the main content. Beyond 3 seconds, a significant share of visitors give up.

My website is only slow on phones, why?
Because the mobile connection is less stable and the processor less powerful: heavy images and scripts weigh twice as much. The PageSpeed test in mobile mode shows it immediately.

Does a “caching plugin” fix the problem?
It masks cause #3 by keeping a copy of the built pages. It's useful on a CMS, but it does nothing about images, scripts or hosting.

Does speed matter to Google?
Yes, it has been an official ranking factor on mobile since 2018, and the “Core Web Vitals” precisely measure the loading experience.