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

CO₂ & EmpCo

What does it mean if more than half of the data comes from external servers?

Many websites load fonts, videos, maps, libraries and analytics services from servers of other providers. While loading, the check separates the bytes that come from the page’s host name from those of other servers. If more than 50 % come from third-party servers, the finding is raised. It names the five third-party servers with the most KB.

Why the share matters

What a third-party server delivers is determined by its operator: file size, compression, caching and the electricity of its data centre. Every third-party server also needs its own connection. A high third-party share means that a large part of the page’s weight and CO₂ value is outside your control.

The link to Data & Law

Every request to a third-party server passes the visitor’s IP address to that provider. Fonts that load from third-party servers before consent are reported by the Data & Law audit area (“Data protection” in the report) as a separate finding; libraries from third-party servers are listed there. If you serve both yourself, these entries disappear and the third-party share falls.

What you can serve yourself

Fonts can be downloaded and served from your own domain, including those from Google Fonts. The same applies to libraries such as jQuery or Swiper, to icons and to images. Videos and maps can be embedded with a preview image that loads the third-party content only on a click.

Examples

Font

Not met

<link rel="stylesheet" href="https://fonts.googleapis.com/css2?family=Roboto:wght@100..900">

Passes

@font-face {
  font-family: "Roboto";
  src: url("/schriften/roboto-var.woff2") format("woff2");
  font-weight: 100 900;
  font-display: swap;
}

Video

Not met

<iframe src="https://www.youtube.com/embed/abc123"></iframe>

Passes

<a href="https://www.youtube.com/watch?v=abc123" class="video-vorschau">
  <img src="/bilder/video-vorschau.webp" width="640" height="360"
       alt="Video auf YouTube ansehen: So läuft eine Prüfung ab">
</a>

Read the five largest third-party servers with their KB in the finding and start with the largest.
Download fonts and libraries and serve them from your domain.
Embed videos and maps with a preview image that loads the third-party content only on a click.
Keep the services whose reports you read and remove the rest.

Deutsche Fassung dieser Seite

FAQ

What counts as your own server?

Your own are files from the page’s host name and from names below it. If the page is on www.example.at, files from example.at or images.example.at count as third-party, as does a CDN under a different name, even if it delivers your files.

Why does the finding name the servers?

So that you can see where the data volume comes from. The finding names the five third-party servers with the most KB during the page view.

Does the third-party share count in the CO₂ score?

It acts through two other items: the third-party bytes are part of the page weight and of the number of requests, and both enter the score.

Why is the share smaller than in the browser’s Network tab?

The browser reports the size of a third-party file if its server releases it with the Timing-Allow-Origin header; the other files count as 0 KB here. What an embedded player or map loads by itself is outside this rule; it counts in the page weight. The share in the finding is therefore a lower bound.