Write descriptive alt text on every meaningful image so AI knows what they show
Every img element needs an alt attribute, descriptive for content images and empty for decorative ones.
What this signal tests
We check that every img element on your page has an alt attribute. Decorative images may use an empty alt="" to signal that they carry no information. For content-bearing images, the alt should be roughly four to two hundred fifty characters, should describe the image's purpose, and should not be filler like "image", "photo", or the raw filename such as "DSC1234".
Why it matters for your visibility in AI
Multimodal AI systems can analyze images directly, but doing so is slow and expensive compared to reading the alt text the page already supplies. Crawlers almost always lift alt as the cheapest, highest-confidence label for what an image shows. Bad or missing alt text means your product photos, infographics, and diagrams contribute nothing to your page's text representation - they become invisible to retrieval. The concrete consequence is that a recipe page with no alt text on its dish photos competes against a fully captioned competitor for any visual query. Even worse, filler alt text like "image1.jpg" pollutes the text representation with noise, actively making your page less retrievable than one with no images at all.
Pass criteria at a glance
| Criterion | Passes when |
|---|---|
| >=95% have alt attribute AND >=80% of non-decorative images have non-empty quality alt or figcaption. |
How we test it
We extract every img element, check whether the alt attribute is present, and apply quality heuristics: length within the four-to-two-hundred-fifty character window, no exact match to the image filename or src basename, no generic deny-list values like "image", "untitled", or pure numeric strings, and no excessive duplication across the page. A page passes when at least ninety-five percent of images carry the attribute and at least eighty percent of non-decorative images have quality descriptions.
Show technical detection method
Parse <img>; check alt presence; quality heuristics on length, generic patterns, src-basename equality, dup count.
If your site fails: how to fix it
- In WordPress, add alt text in the Media Library's per-image fields and in the block editor's image block - both surface the alt attribute on rendered output for every page that uses the image.
- For e-commerce product photos, write alt text that describes what is visible plus the product identifier, for example "Black leather Chelsea boot, side view" rather than "product-img-3-final.jpg".
- For decorative images that exist purely for visual rhythm (background textures, divider icons), use alt="" so AI extractors know to skip them rather than guessing at content.
- For infographics and charts, supplement short alt text with a longer caption or surrounding prose that conveys the data, since alt has practical length limits and complex visuals need more.
- Audit existing alt values for filename leakage ("DSC1234.jpg", "hero-banner-v2-final-final.png") and rewrite them as descriptions, since these patterns are common when alt is auto-populated by upload tools.
Quick facts
| Maturity | ESTABLISHED |
|---|---|
| Weight | high |
| Category | Content Clarity |
Primary sources
Related signals
Frequently asked questions
Does empty alt text fail the check?
Empty alt="" is correct for decorative images and passes the check; it explicitly tells crawlers and assistive technology that the image is non-informational. The failure case is a missing attribute entirely, or a value that is just filler. Use empty alt deliberately, not as a shortcut.
How long should alt text be?
Aim for roughly four to two hundred fifty characters. A few words is fine for a simple product photo; longer descriptions suit complex visuals like charts. For images requiring more than two hundred fifty characters of explanation, supplement with a figcaption or surrounding paragraph rather than stuffing the alt attribute.
Are AI image-recognition tools enough to skip alt text?
No. Crawlers prefer alt text because reading text is orders of magnitude faster and cheaper than running vision models on every image. Even when vision is used, your alt text serves as the authoritative caption and overrides the model's guess - useful when the visual is ambiguous or context-dependent.
Should I include keywords in alt text for SEO?
Describe the image accurately first; keywords second. AI ranking systems penalize keyword-stuffed alt text the same way they penalize stuffed body content. A natural description that happens to mention relevant terms is ideal; a contrived string of keywords is a regression for both classic SEO and AI ingestion.
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