Definition
Alt text, short for alternative text, is a written description of an image added in the page’s code. Screen readers read it aloud for people who cannot see the image, and browsers show it when an image fails to load. It tells both people and machines what an image contains.
Use Cases
Alt text is used to make images accessible to visitors using assistive technology, and to give search engines a clear idea of what each image shows. Good alt text describes the image plainly, such as “stacked bar chart of website types”, rather than stuffing in keywords.
Why It Matters for SEO
Alt text matters for SEO because it is a key part of image SEO, helping images appear in image search and adding context to the page around them. It also supports accessibility, which overlaps with the quality signals search engines reward. Clear descriptions help your visuals get found and understood.
Related Concepts
Related concepts include image SEO, page speed, and accessibility. Describing and optimizing images well helps them load fast, rank, and reach every visitor. This fits into broader work on SEO for Google and AI search.