Alt text

What it means

Alt text is a short description of an image written in the alt attribute of the page code. A screen reader reads it out to blind users, and the browser shows it when the image fails to load.

Under the WCAG accessibility guidelines, every image that carries information, such as a chart, diagram or product photo, needs a text alternative. Purely decorative images should have an empty alt so the screen reader does not hold the user up.

Alt text also helps SEO: search engines use it to understand what an image shows and may display it in image search. Its main purpose, however, is accessibility, not keywords.

How it works in practice

Good alt text describes what the image means in context, not what it looks like. For a sales chart, „chart“ is not enough; „sales grew from 1.2 to 1.8 million euros between 2022 and 2024“ is. For a logo, the company name suffices.

Since 2025 the Accessibility Act applies, placing duties on certain private services such as online shops and banking. Missing alt text is one of the most common findings in accessibility audits.

In content management systems alt text is entered when an image is uploaded. Making it a required field ensures it is not forgotten when content is added.

What to watch out for

A common mistake is to put a list of keywords or a file name such as „IMG_2034.jpg“ in the alt attribute. Such text does not help readers, and search engines may treat it as manipulation.

If important text is part of an image, such as a price on a banner, it must also be in the alt text or, better, in the HTML itself. Otherwise neither a blind user nor a search engine can read it, and with responsive design it is often lost on mobile too.