Re: [csswg-drafts] [mediaqueries-5] Privacy concerns about the prefers-reduced-data media feature (#10076)

There are certainly many helpful use cases this would enable, including loading lower resolution media in low data environments, which can be very impactful.

An alternative which wouldn’t expose more data than is already available in browsers, would be a media query for consuming network status similar to the [`navigator.connection.effectiveType`](https://developer.mozilla.org/en-US/docs/Web/API/NetworkInformation/effectiveType) values in the Network Information API:

```css
@media (min-network-effective-type: 4g) {
  /* bandwidth intensive image or font downloads for example */
}
```

```html
<!-- img which downloads lower resolution images on slower networks -->
<img
  src="example-400w.jpg"
  srcset="example-400w.jpg 400w, example-800w.jpg 800w, example-1200w.jpg 1200w"
  sizes="(min-network-effective-type: 4g) 100vw, 400px"
>
```

But this is still different from the user _preference_ expressed by a `prefers-reduced-data` query, which seems valuable in its own way, as a connection can be fast but still limited/expensive.

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Received on Thursday, 16 October 2025 12:28:45 UTC