What Is Alt Text? SEO & Accessibility Definition with Examples

Alt text (alternative text) is the value of an image's alt attribute in HTML. It serves two audiences: screen readers that read alt text aloud for visually impaired users, and search engines that cannot interpret image pixels the way humans do. When an image fails to load, browsers display the alt text in its place. It is one of the few HTML attributes that simultaneously affects accessibility compliance and image search visibility.

Writing Alt Text That Works

Describe what the image shows in plain language, in context of the surrounding content. A product photo on an ecommerce page might read "Stainless steel French press coffee maker, 34 oz capacity, side view with wooden handle." A decorative hero image that adds no information should use an empty alt attribute (alt="") so screen readers skip it entirely.

Keyword stuffing in alt text — "best SEO tools cheap SEO software buy SEO" — helps neither accessibility nor rankings and can trigger quality filters on image-heavy pages. Include a relevant keyword only when it naturally describes the image content.

Alt Text vs. Other Image Attributes

The title attribute on images is not a substitute for alt text and is largely ignored by screen readers and Google for ranking purposes. File names matter marginally — french-press-coffee-maker.jpg beats IMG_4829.jpg — but alt text carries more weight. Caption text visible on the page provides additional context Google can use alongside alt attributes.

Common Mistakes

Missing alt attributes entirely force screen readers to read the filename aloud — a poor experience and a missed SEO signal. Using identical alt text on every image in a gallery wastes an opportunity to describe each image distinctly. Prefixing with "image of" or "picture of" is redundant; screen readers already announce the element as an image.

Alt text is one piece of on-page technical SEO alongside title tags, heading structure, and page speed. Our technical SEO guide covers image optimization, lazy loading, and modern format delivery (WebP, AVIF) as part of a complete site health audit.