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Performance

Should I use WebP or AVIF instead of JPEG

WebP is typically 25–35% smaller than JPEG at the same visual quality, and AVIF more again. Support is universal now. On an image-heavy page this is usually the single largest download saving available, and it requires no design change.

What 13x checks

This is rule performance.image-formats in the public registry: Modern image formats. It runs on every audit, against the pages we actually fetched, and its result is derived from the response rather than estimated.

Surface
Performance
Score weight
4 of the readiness score
Scope
Reported as skipped when the page renders only with JavaScript
Applies
Only where the market or the page shape makes it relevant

Registry version 2026-07-30. Every rule is published, and the audit is deterministic — the same page produces the same finding every time.

The fix

The same text the audit hands you when this check fails on your own site.

of images are JPEG or PNG. WebP is typically 25–35% smaller at the same visual quality, AVIF more again, and both are universally supported now.

bash code
# One-off conversion
npx @squoosh/cli --webp auto images/*.jpg

# Or with sharp
npx sharp-cli -i "images/*.jpg" -o dist/ -f webp -q 80

To keep a fallback, use <picture>:

html code
<picture>
  <source srcset="/hero.avif" type="image/avif" />
  <source srcset="/hero.webp" type="image/webp" />
  <img src="/hero.jpg" width="1200" height="630" alt="…" />
</picture>

Better still, let your host convert on the fly — Vercel, Cloudflare Images and Netlify all do, so you upload one file and each browser gets the best format it supports.

Framework-specific versions

Where the change differs enough to be worth writing out separately.

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