Alt Text
The alternative text attribute on an HTML image tag that describes the image for search engines and screen readers.
Definition
Alt text (alternative text) is the value of the alt attribute in an HTML <img> tag: <img src="chart.png" alt="Bar chart showing organic traffic growth from 2022 to 2024">. It serves two primary purposes: accessibility (screen readers announce it to visually impaired users) and SEO (search engines cannot see images, so they rely on alt text to understand image content).
For image SEO, well-written alt text can help images rank in Google Image Search, which drives meaningful traffic for visual niches like e-commerce, photography, and infographics. Alt text should describe the image accurately and concisely, include the target keyword where it fits naturally, and be unique for each image on the page.
Common mistakes include leaving alt text blank (which makes images invisible to search engines and inaccessible to screen reader users), using generic phrases like "image1.jpg" or "photo," and keyword-stuffing alt attributes. Decorative images that add no informational value (borders, spacers) should use empty alt text (alt="") so screen readers skip them. Use an image alt checker to audit pages for missing or poor-quality alt attributes.