What is alt text?
Alt text (alternative text) is the alt attribute on an HTML image element. It describes the image for screen readers, displays when an image fails to load, and gives search engines their only reliable textual signal about what an image shows. It is the foundation of image SEO and a legal accessibility requirement in many jurisdictions.
How to write effective alt text
Good alt text is specific and functional. It describes what the image actually shows in the context of the page, includes a keyword only when it genuinely fits, and stays under roughly 125 characters so screen readers handle it gracefully. Decorative images should carry an empty alt attribute so assistive technology skips them.
Alt text matters more in the AI search era. Multimodal models and Google Lens lean on alt attributes and surrounding text to interpret images, and image packs remain a meaningful traffic source for product, recipe, and how-to queries. Sites with systematic alt text gaps cede that surface entirely to competitors.
Example
Example
Weak: alt="image1". Strong: alt="Comparison chart of paid CPC versus organic cost per click over 12 months". The strong version describes the chart and earns relevance for the page topic without stuffing.
Frequently asked questions
Is alt text a ranking factor?
For image search, yes: it is the primary text signal Google associates with an image. For web search it contributes page context, but it will not rescue a thin page on its own.
What should alt text say for decorative images?
Use an empty alt attribute (alt="") so screen readers skip the image. Never omit the attribute entirely; that forces assistive technology to read the file name aloud.