Alt Text

Understanding Alt Text

Alt text is specified in the alt attribute of an HTML <img> tag. Its primary purpose is accessibility — screen readers read alt text aloud to visually impaired users, making images understandable without seeing them. This is not optional: the Web Content Accessibility Guidelines (WCAG) require meaningful alt text on all informative images.

For SEO, alt text serves as a critical signal for Google Image Search. Since search engines cannot see images the way humans do, they rely heavily on alt text (along with surrounding content, file names, and structured data) to understand what an image depicts. Well-written alt text can drive significant traffic through Google Image Search, which accounts for over 20% of all Google searches.

Alt text also provides context when images fail to load, displaying the description in place of the broken image. This ensures users still understand the content regardless of connection quality or browser settings.

Why Alt Text Matters

Beyond accessibility compliance, alt text directly impacts your visibility in Google Image Search — a traffic source most businesses underutilize. Product images with descriptive alt text rank in image search for commercial queries, driving qualified traffic. Informational images with proper alt text can appear in featured snippets and image packs within regular search results.

Google has explicitly confirmed that alt text is one of the factors it uses to understand page content. Images without alt text are missed opportunities — both for ranking in image search and for reinforcing your page's topical relevance to the overall search algorithm.

Best Practices

• Write descriptive alt text that accurately explains what the image shows, not what you want to rank for
• Keep alt text concise — typically under 125 characters — while being meaningfully descriptive
• Include relevant keywords naturally when they accurately describe the image, but never keyword-stuff
• Use empty alt text (alt="") for purely decorative images that add no informational value
• Do not start alt text with 'Image of' or 'Picture of' — screen readers already announce it as an image
• Write unique alt text for every image — avoid duplicating the same description across multiple images