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Image SEO Checker

SEO and marketing

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Alt attributes, file weights, formats and lazy loading.

What the image audit checks

Images are usually the heaviest part of a page. Two or three mistakes here cost more than everything else combined.

The alt attribute A description for anyone who cannot see the image: search engines, screen readers, slow connections. A missing alt and an empty one differ: empty means decorative, missing means forgotten.
File weight A multi-megabyte camera photo in the header is the most common cause of slow loading. We weigh the files and list the heaviest.
Dimensions in the markup Without width and height the browser cannot reserve space and the layout jumps while loading. That feeds straight into the CLS metric.
Modern formats The same shot in webp weighs a quarter less than jpg with no visible difference. We count how many are still in older formats.
Lazy loading Images below the fold should load on scroll. The first two or three should not: deferring them hurts perceived speed.
Broken sources An image returning a 404. Obvious on the page, but easy to miss among a hundred of them.

What a good alt looks like

The rule: describe what is in the image rather than stuffing keywords.

Descriptive “Red sofa with wooden legs in a living room” beats “sofa”, and beats “sofa-buy-cheap-online” by a mile.
Under 125 characters Screen readers cut longer descriptions. If it does not fit, it may belong in a caption rather than an alt.
Empty for decoration Dividers, background patterns, icons next to text. An empty alt says: this carries no meaning, skip it.
No “image of” prefix The screen reader already announced it is an image. Repeating it just wastes the listener’s time.

How much an image should weigh

Under 100 KB A regular in-text illustration. At that size webp gives perfectly decent on-screen quality.
Under 200 KB A full-width hero image. Anything larger is noticeable on a slow connection.
Over 500 KB Almost always means the file was never optimised. Compression will cut it fivefold with no visible loss.
The whole page All images together should ideally stay under 1 MB. On mobile every 500 KB is roughly a second of waiting.

FAQ

How does an empty alt differ from a missing one?
An empty alt is a deliberate signal: the image is decorative and screen readers should skip it. A missing one means the attribute was forgotten, and the reader will try to read the filename aloud. That is why we count them separately.
How much should an image weigh?
An in-text illustration under 100 KB, a hero image under 200 KB. Anything over 500 KB almost always means the file was never optimised — compression will cut it fivefold with no visible loss.
Should every image be lazy-loaded?
No, and this matters. Deferring the first two or three images hurts: they define your LCP, and delaying them worsens the speed score. Only defer what sits below the fold.
Should every image become webp?
For the web, mostly yes: the same shot weighs a quarter less with no visible difference. Not for everything though — logos and icons belong in svg, and print needs other formats. Keep the originals separately.
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