Alt Text

Alt text (alternative text) is a short written description of an image, added to the image’s HTML with the alt attribute. Screen readers read it aloud to people who cannot see the image, browsers display it if the image fails to load, and search engines use it to understand what the image shows.

Written by Paul Hoda, SEO consultant since 2005. Last updated 8 November 2026.

Why alt text matters

  • Accessibility: it is essential for blind and partially sighted users and is required by accessibility standards such as WCAG.
  • Image search: alt text is one of the main signals Google uses to rank images in Google Images.
  • Context: it helps search engines understand how an image relates to the surrounding content.
  • Linked images: when an image is a link, its alt text acts like Anchor Text.

How to write good alt text

  1. Describe what the image shows, as you would to someone on the phone.
  2. Be specific: “Dentist explaining a dental implant model to a patient” is better than “dentist”.
  3. Keep it concise: usually one short sentence, around 125 characters or less.
  4. Include a keyword only if it fits naturally and accurately describes the image.
  5. Do not start with “image of” or “picture of”; screen readers already announce it as an image.
  6. Add context that matters: for a chart, state the key takeaway, not just “chart”.
  7. Describe the function for linked or button images: “Download the SEO audit checklist” rather than “arrow icon”.

Examples

  • Poor: alt=”seo seo london seo consultant seo services”
  • Poor: alt=”image1″
  • Better: alt=”SEO consultant reviewing a website audit”
  • Best: alt=”Google Search Console performance graph showing organic clicks doubling over six months”

When to use empty alt text

Purely decorative images, such as background flourishes, dividers or icons next to text that already says the same thing, should have an empty alt attribute (alt=””). This tells screen readers to skip them. Do not leave the attribute out entirely, because some screen readers will then read the file name.

Alt text vs title text vs captions

  • Alt text replaces the image for people who cannot see it.
  • Title attribute shows a tooltip on hover; it adds little for SEO or accessibility.
  • Captions are visible text under the image, read by everyone. They are useful for adding context and are widely read.

Alt text for complex images

For infographics, detailed charts and diagrams, use concise alt text that states the main point, and provide the full information in the surrounding text or a linked description. This helps everyone, including search engines that cannot fully interpret complex visuals.

How to audit alt text

SEO crawlers and accessibility checkers can list images with missing alt attributes. Review them in batches, starting with images on your most important pages. On WordPress, alt text is set in the Media Library, so you can fix it once for images used on several pages. For more on optimising images overall, see Image SEO.

Key Takeaways

  • Alt text describes images for screen readers and search engines.
  • Be specific and concise, describing what the image actually shows.
  • Include keywords only when they describe the image accurately.
  • Use empty alt text for purely decorative images.
  • For charts, state the key takeaway.

Related Terms

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