Alt Text Quality

Alt text quality is about usefulness, not keyword density. Good alt text tells a screen reader user what matters in the image and fits the page context; bad alt text is vague, stuffed, repetitive, or added to decorative images that should use alt="".

For SEO, the value is real but limited. Google uses image context, surrounding copy, filenames, structured data, and the image itself. Alt text is one signal. Not the signal.

What good alt text actually looks like

The standard is simple: describe the image as specifically as needed, then stop. For a product page image, "women's black leather ankle boots with side zip" is useful. "boots" is too thin. "buy cheap black leather ankle boots online best boots sale" is spam.

Length matters less than clarity. In practice, 60-125 characters is a solid range for most commercial images, but there is no magic cutoff in Google Search. Google's documentation says alt text should be concise and informative. That's the bar.

Why SEOs should care

• Accessibility: This is the main reason. If the image conveys meaning, the alt text should carry that meaning for screen readers.
• Image search relevance: Better descriptions can help Google understand image content, especially on product, recipe, and how-to pages.
• Topical reinforcement: Alt text can support entity understanding when it aligns with captions, nearby copy, and schema.

The caveat: alt text alone rarely moves rankings on competitive web search queries. If a page has weak internal links, thin copy, and poor backlinks, rewriting 5,000 alt attributes will not save it.

How to audit alt text quality

Use Screaming Frog to export image URLs, alt text, and image size data. In Google Search Console, check Image Search performance by page and query. In Ahrefs or Semrush, map pages that already earn image visibility, then prioritize templates that matter: PDPs, category pages, and high-traffic editorial pages.

Look for four failure patterns:

1. Missing alt text on meaningful images
2. Decorative images with noisy alt text
3. Duplicate alt text across hundreds of distinct images
4. Keyword stuffing driven by CMS rules or bulk AI generation

If you use AI to draft alt text, QA it aggressively. Vision models still misidentify products, charts, and UI states. A 5-10% manual sample per batch is the minimum. More if the site is medical, legal, or enterprise ecommerce.

Practical standards

• Decorative images: use alt=""
• Functional images: describe the action or destination, not the pixels
• Product images: include product type and distinguishing attributes
• Charts and infographics: summarize the takeaway, not every visual detail

John Mueller has repeatedly said alt text helps Google understand images, but it should primarily serve users. That's the right framing. Write for accessibility first. Take the SEO lift when it comes.