What is Alt Text (Alternative Text)?

Alt text, short for alternative text, is a description of an image provided through the alt attribute of an HTML img element. Its primary purpose is accessibility: screen readers read the alt text aloud so that people who are blind or have low vision understand what an image conveys. It also displays in place of an image when the file fails to load or is blocked.

Beyond accessibility, alt text helps search engines understand image content, since they cannot 'see' pictures directly. Descriptive alt text is a factor in image search rankings and contributes context to the surrounding page. This dual role — serving both assistive technology and search crawlers — makes well-written alt text a small but genuinely valuable piece of on-page optimization.

Good alt text describes the image accurately and concisely in the context of the page. Instead of a vague 'image' or a stuffed list of keywords, it states what matters: 'Bar chart showing email open rates rising from 18% to 34% after subject-line testing.' The right level of detail depends on the image's function — decorative images should have an empty alt attribute so screen readers skip them.

Common mistakes include omitting alt text entirely, keyword-stuffing it, restating the caption verbatim, or beginning with redundant phrases like 'image of'. For functional images such as buttons or links, the alt text should describe the action, not the appearance. Auditing pages for missing or poor alt text improves both accessibility compliance and image SEO simultaneously.