Methodology: This check follows wSEO methodology 1.0. How the assessment works

Inspect the file actually delivered

How to audit image formats

DevTools reveals the selected URL, MIME type and transfer size. Pair the technical check with a visual comparison, fallback test and desktop/mobile review.

Auditing image format, weight and quality in a browser
A URL extension alone does not prove the response format.

Quick browser check

  1. Open a representative page and DevTools → Network, enable Disable cache and reload.
  2. Select Img. Record Request URL, Content-Type, Transferred and Resource Size.
  3. Select the img in Elements and run $0.currentSrc in Console to see the chosen URL.
  4. Compare with the source at real display size: text, faces, gradients, transparency and animation.
  5. Repeat at a narrow viewport and confirm mobile does not receive an oversized asset.

How to rate findings

Image-format issue priority
ObservationRatingAction
Variant is smaller and visually soundGoodRecord the result
AVIF/WebP exists but fallback is always deliveredMediumCheck source, type, Accept and cache
New file is larger or visibly degradedHighRe-encode or keep the original
404, lost transparency or broken animationCriticalRestore fallback before release

Whole-page inspection

[...document.images].map(img => ({ currentSrc: img.currentSrc, natural: [img.naturalWidth, img.naturalHeight], rendered: [img.clientWidth, img.clientHeight] }))

This finds actual URLs and excessive intrinsic dimensions. Read weight and MIME type from Network.

False conclusions and scope

  • An extension may not match the payload; inspect Content-Type.
  • A CDN may negotiate from Accept, so browsers can receive different responses.
  • Cache can conceal changes; repeat measurements without cache.
  • Estimated lab savings are not the actual control-page gain.
  • Format checks do not validate alt, cropping, licensing, LCP priority or responsive markup.

Use the repair guide; template implementation is covered by the service.