Warum zeigt PageSpeed Insights mobil so viel schlechtere Werte als am Desktop?

Der mobile Test simuliert ein durchschnittliches Smartphone mit gedrosselter Verbindung und schwächerem Prozessor. Große Bilder und viel JavaScript wirken sich dort deutlich stärker aus, deshalb ist der mobile Wert der wichtigere.

Reicht ein Caching-Plugin, um die Website schneller zu machen?

Oft ist es ein wichtiger Baustein, allein reicht es selten. Ein falsch eingestelltes Caching kann sogar wirkungslos bleiben, zum Beispiel wenn Mobilgeräte keine zwischengespeicherten Seiten erhalten. Außerdem hilft Caching kaum gegen übergroße Bilder oder blockierende Skripte.

Manchmal. Eine lange Serverantwortzeit spricht für ein Problem bei Hosting, PHP-Version oder Datenbank. Ist der Server schnell und die Seite trotzdem träge, liegt die Ursache meist in Medien und Skripten auf der Seite selbst.

Wie schnell sollte eine Website laden?

Als Orientierung gelten die Grenzwerte von Google: ein LCP unter 2,5 Sekunden, ein INP unter 200 Millisekunden und ein CLS unter 0,1, jeweils gemessen an mindestens 75 Prozent der Seitenaufrufe.

Wann sehe ich die Verbesserung in der Google Search Console?

Die Felddaten beruhen auf den Aufrufen der letzten 28 Tage. Verbesserungen werden dort deshalb schrittweise sichtbar, während eine Labormessung sie sofort nach der Umsetzung zeigt.

Loading time and Core Web Vitals

Website too slow: measure the causes and fix them specifically

If your website is too slow, it is almost always due to a few clearly measurable causes: a sluggish server response, images and videos that are too large, incorrectly configured caching or too much JavaScript. Measuring first and then addressing the biggest lever achieves noticeable improvements with manageable effort.

I analyze your website using lab and field data, identify the causes specifically and fix them in the server, theme and content. I demonstrate the result with a new measurement.

Elias Arndt

Web development, programming and AI
★★★★★ 5,0 on Google

Request a project

Describe your project in a few sentences. You will receive a personal response.

How to recognize that your website is too slow

Your own perception is often misleading. On an office PC with a fast connection and a filled browser cache, a website may seem fast, while on an average smartphone using a mobile network it remains blank for several seconds. Measurement on mobile devices is therefore meaningful, because that is where most visitors are.

Google evaluates the loading experience using three metrics, the Core Web Vitals. Largest Contentful Paint (LCP) measures when the largest visible element appears and should be under 2.5 seconds. Interaction to Next Paint (INP) measures how quickly the page responds to clicks and inputs; the target value is under 200 milliseconds. Cumulative Layout Shift (CLS) records how much content shifts while loading and should remain below 0.1.

The difference between lab data and field data is important. PageSpeed Insights displays the values of real Chrome users from the last 28 days at the top and a simulated test below. The two values can differ significantly, and Google uses the field data for its evaluation.

If your website no longer loads at all or displays a blank page, this is an outage with other causes. For that, there is the page WordPress no longer loads.

The most common causes of long loading times

The same bottlenecks appear again and again in my analyses. Usually, two or three of them work together.

Sluggish server response

If the server takes a long time to deliver the first byte, everything else is delayed. Causes include overloaded hosting plans, old PHP versions or complex database queries on every request.

Faulty caching

A caching plugin is quickly installed, but it is not always configured correctly. Some configurations do not serve cached pages to mobile devices at all, without this being noticeable on desktop.

Oversized media

Photos straight from the camera and full-resolution background videos often account for the largest share of the data. Modern formats such as WebP or AVIF and suitable image sizes for each device reduce it considerably.

Too much JavaScript

Page builders, sliders and animations load scripts that the browser must process before the page responds. This particularly worsens the INP score on weaker smartphones.

Third-party scripts

Tracking, chat widgets, map services and cookie banners are loaded from external servers. Every individual script takes time, and their combined impact is often underestimated.

Webfonts and layout shifts

Fonts that are loaded late and images without fixed dimensions cause content to jump while loading. This worsens the CLS score and leads to misclicks.

A sprawling plugin landscape

Extensions added over the years often load their files on every page, even where they are not needed.

This is how I make your website faster

Measure

I collect field data and lab data for the most important page types, separately for mobile devices and desktop. This creates a baseline against which every change can be measured.

Narrowing down the causes

Based on the loading order in the waterfall chart and the browser’s resource usage, I determine which resources are delaying the LCP and which scripts are blocking the response.

Implement the biggest levers

I begin with the measures that deliver the most benefit relative to the effort involved, such as caching configuration, image compression, deferred script loading and HTTP/2. I test all changes first in a preview environment.

Measure again

After going live, I repeat the measurement under the same conditions. Google’s field data is updated over 28 days, which is why I check it again after a few weeks.

Keep up

New plugins and large images can gradually make the loading time worse again. With regular website maintenance, such setbacks are noticed early.

From practice: my own website and an association’s website

At eliasarndt.de too, the mobile PageSpeed score was initially only 68. One of the causes was a caching plugin that did not serve cached pages to mobile devices; this was not noticeable on desktop. After the correction and further optimizations, the score is 95 on mobile and 99 on desktop. The Accessibility score in Lighthouse rose from 86 to 100 at the same time.

The cause was different for the website of an association from Schleswig. The homepage loaded around 60 MB of videos and images. Through new media encoding, the amount of data fell to 16 MB without any visible content having to be removed.

Both cases show why measurement comes first. The symptoms were similar, but the effective measure was completely different in each case.

When optimizing alone is no longer enough

Some websites are built on a foundation that can only be sped up to a limited extent, for example a heavy page builder with many nested elements or an outdated system without updates. In that case, it is worth comparing it with a website relaunch, for example on the basis of a lightweight framework such as Astro, which delivers hardly any JavaScript by default.

A fast website alone does not lead to better rankings on Google, because loading time is just one factor among many there. However, it reduces the bounce rate and makes forms and checkout more pleasant for your visitors. Anyone who is reworking images and code anyway can improve the website accessibility at the same time.

Frequently asked questions about slow websites

Why does PageSpeed Insights show much worse scores on mobile than on desktop?

The mobile test simulates an average smartphone with a throttled connection and a weaker processor. Large images and a lot of JavaScript have a much stronger impact there, which is why the mobile score is the more important one.

Is a caching plugin enough to make the website faster?

It is often an important building block, but it is rarely sufficient on its own. Incorrectly configured caching can even remain ineffective, for example if mobile devices do not receive cached pages. Caching also does little to help with oversized images or blocking scripts.

Is it the hosting?

Sometimes. A long server response time points to a problem with hosting, the PHP version or the database. If the server is fast but the website is still sluggish, the cause is usually the media and scripts on the page itself.

How quickly should a website load?

As a guide, Google’s thresholds are an LCP below 2.5 seconds, an INP below 200 milliseconds and a CLS below 0.1, each measured across at least 75 percent of page views.

When will I see the improvement in Google Search Console?

The field data is based on visits from the last 28 days. Improvements therefore become visible gradually, while a lab measurement shows them immediately after implementation.

Let’s find out what is slowing down your website

Tell me your website address and the pages that are most important to you. In the free initial consultation, I will show you where the biggest bottlenecks are and which measures are worthwhile.

Available Monday to Friday from 8 a.m. to 8 p.m. Related topics: WordPress no longer loads · Website relaunch · Make your website accessible · WordPress maintenance · Web development, programming and AI