Modern image formats

Silktide loads your pages in a real browser and identifies images that would be meaningfully smaller if served in a modern format such as WebP or AVIF. Each image is reported with its current size and the saving a modern format would give.

Why this matters

WebP and AVIF compress images far better than the older JPEG and PNG formats - often 25-50% smaller at the same visible quality. Since images are usually most of a page's weight, converting them is one of the largest single performance wins available, and it requires no visible change to your site. Faster pages keep more visitors and feed into search ranking through .

All modern browsers support WebP, and AVIF support is now near-universal, so the historical reason to avoid these formats has gone.

How to fix it

Convert the reported images to WebP or AVIF. Most image tools export both, and many and can convert automatically on upload or delivery - the automated route stops the problem recurring.
If you need to support very old browsers, serve a fallback:

<picture>
  <source srcset="photo.avif" type="image/avif">
  <source srcset="photo.webp" type="image/webp">
  <!-- Older browsers fall back to the JPEG -->
  <img src="photo.jpg" alt="Team at the summer off-site">
</picture>

How Silktide tests this

Load the page in a real browser and collect the images it displays.
Estimate what each JPEG or PNG image would cost in a modern format.
Report images where the saving is meaningful (at least 8 KB), with the current size and the potential saving, largest first.

Troubleshooting

How does this differ from the other image checks?

This check is specifically about format conversion. Compressing images within their current format is covered by Image compression and, in more depth, by Image optimisation; serving images at the right dimensions is covered by Responsive images. The same image can appear in several - the fixes are complementary.

Our platform can't serve WebP or AVIF

A in front of your site can often convert images on the fly without platform changes. Failing that, compressing the originals well still captures much of the benefit - see Image optimisation.