Is prefetch bad in principle?

For a small page that a visitor is very likely to open next, it saves waiting time. The finding depends on the file extension: video, audio, archive and PDF, regardless of size.

preload loads a file that the current page needs immediately, such as the hero image. Duplicate or unused preload hints are reported by the Performance audit area.

Does my CMS insert such hints by itself?

Some speed-up extensions do. Check in their settings which files they set prefetch for.

This translation has not been editorially reviewed yet. The German version is authoritative. Deutsche Fassung

CO₂ & EmpCo

Why should videos and PDFs only load when someone clicks?

With <link rel="prefetch"> a page tells the browser: the visitor probably needs this file next, load it in the background. For the next small page this makes sense. If the hint points to a video, an archive or a PDF, Chrome, Edge and Firefox load the file on every visit; only those who open it benefit. The check reports this with the address of the file.

What the check looks for

It reads all link elements with rel="prefetch" and reports those whose address ends in .mp4, .webm, .mov, .zip, .pdf, .mp3 or .wav, regardless of the size of the file. The finding names the number, up to five, and one address as an example.

Why this weighs heavily

A company video easily has 20 MB, a price list as PDF several MB. Loaded in advance, such a file multiplies the data volume of the page view, in Chrome, Edge and Firefox for every visitor, also on mobile networks. Only those who open the file benefit.

Examples

Company video

Not met

<link rel="prefetch" href="/medien/imagefilm.mp4">

Passes

<video controls preload="none" poster="/medien/imagefilm-vorschau.webp">
  <source src="/medien/imagefilm.mp4" type="video/mp4">
</video>

Price list

Not met

<link rel="prefetch" href="/downloads/preisliste-2026.pdf">

Passes

<a href="/downloads/preisliste-2026.pdf">Preisliste 2026 (PDF, 3,2 MB)</a>

Search the source code for rel="prefetch" and check what the hints point to.
Remove prefetch for videos, archives, audio and PDFs.
Link such files as usual; they then load only when someone clicks.
Keep prefetch only for small files that the next page certainly needs.

Deutsche Fassung dieser Seite