What is alt text, and how much does it really matter?
A short written description of an image, read aloud to people using screen readers and read silently by every machine that processes your page. It matters most for images that carry meaning — and, counterintuitively, the right description for a decorative image is no description at all.
What it actually is
An image is opaque to anything that cannot see it. Alt text is the sentence that stands in for it: what the picture shows, or what it is for. It is not a caption and not a place for keywords — it is what you would say if you were describing the page to someone over the phone.
Why it matters
Three audiences at once. People using screen readers rely on it entirely, and in many jurisdictions that is an accessibility obligation rather than a courtesy. Search engines use it to understand images they cannot otherwise interpret. And AI assistants summarising your page treat it as part of the content — so an unlabelled product photo is a product an assistant does not know you sell.
What good looks like
Every meaningful image described in plain language, and every purely decorative one explicitly marked as decorative so assistive technology skips past it rather than announcing a filename. That distinction is the part most sites miss: a blank description on a meaningful image and a chatty one on a background flourish are both wrong, in opposite directions.
Being honest about it
On most marketing sites this is a moderate SEO factor and a significant accessibility one, and we would weight the second more heavily than the first. If you sell physical products or your images carry real information, it climbs sharply. If your site is mostly text with a few background textures, correctly marking those as decorative is genuinely all that is required.
Where most sites go wrong
The dominant pattern on content-managed sites is images that have a description field nobody ever filled in, so every gallery, product thumbnail and article header arrives blank. Because the field technically exists, automated checks often report no problem at all — the description is present and empty, which reads as "this image means nothing". The other classic is a filename left in place as the description, which tells a screen-reader user your image is called a string of digits.