Alt text (alternative text) is a short description that conveys the content and function of an image in words; in HTML it is defined with the alt attribute of the img element. Screen readers read the alt text when announcing an image, and browsers display it when the image fails to load. WCAG requires a text alternative for every image that carries information.
Text alternatives are among the first requirements of WCAG's perceivable principle: every piece of visual content that carries information must also be expressed in text. In HTML this is done with the alt attribute of the img element. Alt text is announced by screen readers, displayed by browsers when an image fails to load, and helps search engines understand the image, so it matters for both accessibility and SEO. Good alt text conveys the function of the image on the page: it identifies the product in a product photo, summarizes the data in a chart, and states the destination when an image acts as a link.
Purely decorative images should have an empty alt attribute so screen readers skip them silently instead of producing noise. Copying the file name, stuffing keywords or starting every alt text with the word image are common mistakes; screen readers already announce that the element is an image. On large sites, auditing thousands of images by hand is impractical, so automated scanning quickly lists missing alt texts page by page. Prioritize images that carry information, and make the alt text field a mandatory part of your CMS content workflow. Regular scanning then catches gaps in newly added images early.
Frequently asked questions
How should alt text be written?
Write short, concrete and context-aware descriptions: convey the function of the image on the page in one or two sentences. For a product photo, name the product and its distinguishing feature; for a chart, summarize the main finding; for an image that acts as a link, state the destination. Do not start with the word image, do not use the file name and do not stuff keywords. Staying under roughly 125 characters is good practice.
Do decorative images need alt text?
No, but the alt attribute should not be removed entirely. Decorative images get an empty attribute value, which tells screen readers to skip the image. If the attribute is missing altogether, some screen readers read the file name, which creates a poor experience. A practical test for whether an image is decorative: if removing the image would remove information from the page, it is not decorative and needs alt text.
This content is for information only and is not legal advice.