Alt text

Alt text is the short description you attach to an image in the code. Visitors usually don't see it, but it's there: screen readers read it aloud to blind and partially sighted users, browsers show it when an image doesn't load, and search engines use it to understand what's in a picture. In HTML, it's the alt attribute of the img tag.

So alt text is first and foremost a matter of accessibility. The fact that it also helps people find you is a nice bonus, but it should never become the main goal. If you write for the person who can't see the image, you'll usually write good text for search engines automatically too.

Why is alt text important?

Search engines are getting better and better at analysing images, but a good description remains a clear signal. Google itself says it uses alt text, together with the surrounding text, to understand the content of an image. That helps your images appear in Google Images and contributes to the overall understanding of your page.

On top of that, an accessible website is increasingly part of the basics. Under the European Accessibility Act, many online services, including many online stores, have had to meet accessibility requirements since 2025. If in doubt, have someone check whether that applies to your business.

How to write good alt text

• Describe what can actually be seen, in a short sentence. Imagine explaining it to someone over the phone.
• Give context that matters. On a product page, the brand or colour is relevant; in a blog post, perhaps the situation.
• Avoid "image of" or "photo of". Screen readers already announce that it's an image.
• Don't stuff it with a list of keywords. That helps nobody and can come across as spam.
• Leave decorative images empty with an empty alt attribute, so screen readers skip them.

An example: a florist in York shows a bouquet in its online shop. Weak alt text is "bouquet1.jpg" or "flowers York florist cheap". Strong alt text is "Round bouquet of white roses, eucalyptus and lisianthus wrapped in kraft paper". That's useful for a screen reader and gives a search engine a clear picture of the product.

Alt text and AI search

AI applications such as Gemini and ChatGPT are also increasingly processing images and the text around them. A clear description makes your content unambiguous, which only becomes more important in an age of multimodal search. Good alt text is also part of a broader approach to on-page SEO, together with clear headings, a good meta title and fast page speed, where compressed images also play a part.

Tracking down common mistakes

On websites with hundreds of images, checking everything by hand is an impossible task. Missing or automatically filled-in alt text, such as file names, is very common. With a technical SEO analysis, you can quickly see which images are still missing a description, so you can update them in a targeted way, starting with your most important pages. Then make it a habit: whoever uploads a new image to the CMS fills in the alt text straight away.