ONPAGE · SEO GLOSSARY

Alt Text (Image Alt Attribute)

A text description of an image, written in the HTML `alt` attribute — required for accessibility and used by search engines to understand image content.

Definition

Alt text (alternative text) is the `alt` attribute on an HTML `<img>` element: `<img src="chart.png" alt="Bar chart showing LCP scores by CMS platform">`. It serves two audiences: screen readers (read aloud to users who can't see the image) and search engine crawlers (which index alt text to understand what an image depicts and index the image in Google Images). Decorative images that add no informational value should have empty alt text (`alt=""`) so screen readers skip them.

Why it matters for SEO

Missing alt text is an accessibility failure — the Web Content Accessibility Guidelines (WCAG) require it at Level A, the lowest compliance threshold. For SEO, images without alt text pass zero keyword signal to Google Images and miss an opportunity to reinforce the page's topical relevance. For blog posts, infographics, and tool screenshots, descriptive alt text that naturally includes relevant terms adds a modest but real relevance signal. Google can understand images directly (using Google Lens-style vision), but explicit alt text is still an explicit signal it prefers over inference.

How DeepSEOAnalysis checks this

The audit checks every `<img>` element on crawled pages for the presence of an `alt` attribute. Images missing `alt` entirely are flagged as warnings (accessibility and SEO gap). Images with `alt=""` are treated as intentionally decorative and not flagged. Images with very long alt text (over 125 characters) are flagged as info-level (alt text should be concise and descriptive, not a keyword list).