Alt Text SEO
Alt text is the HTML text alternative for an image, used to describe the image’s content or function when the image cannot be seen.
Key takeaways
Alt text serves two critical roles: it makes images accessible to people using screen readers and helps search engines understand what an image shows.
Example: Writing Alt Text for a Product Image
- Image: A red ceramic coffee mug with a wooden handle, photographed on a white background.
- Poor alt text:
alt="mug"(too vague) - Better alt text:
alt="Red ceramic coffee mug with wooden handle on white background"(describes content and context) - Best alt text:
alt="Red ceramic coffee mug with wooden handle"(concise, descriptive, under 125 characters)
Quick-Start: How to Write Alt Text in 5 Steps
- Identify the image’s purpose: Is it informative, decorative, or functional (e.g., a button)?
- Describe what’s important: Focus on the content or function the image conveys.
- Keep it concise: Aim for under ~125 characters.
- Use natural language: Include relevant keywords only if they fit naturally.
- Add the alt attribute in your HTML:
<img src="mug.jpg" alt="Red ceramic coffee mug with wooden handle">
How to Judge If Your Alt Text Is Effective
- Does it describe the image’s content or function without being overly verbose?
- Would a screen reader user get the same information as a sighted user?
- Is it free of redundant phrases like “image of” or “picture of”?
- Does it avoid keyword stuffing?
- For decorative images, is the alt attribute empty (
alt="")?
Common Alt Text Mistakes to Avoid
- Leaving alt text blank for meaningful images: This makes the image invisible to screen readers and search engines.
- Keyword stuffing: Forcing keywords like “buy red mug online” when the image is just a mug.
- Writing vague text: Using “image” or “photo” instead of a useful description.
- Repeating the caption or surrounding text: Alt text should complement, not duplicate, nearby content.
Next step
FAQ
What is alt text?
Alt text (alternative text) is an HTML attribute added to an image tag that provides a text description of the image. It is used by screen readers for accessibility and by search engines to understand image content.
Does alt text help SEO?
Yes. Alt text helps search engines index images properly, which can improve visibility in image search results. It also contributes to overall page relevance when keywords are used naturally.
How long should alt text be?
Keep alt text under about 125 characters for optimal screen reader usability. For complex images like charts, provide a short summary in alt text and a longer description nearby.
Should I use keywords in alt text?
Yes, but only if they naturally describe the image. Avoid keyword stuffing, as it harms both user experience and SEO.
Related topics
Sources
- Google Search Central — Google’s primary guidance on image indexing and image SEO best practices.
- WebAIM — Widely cited accessibility reference for writing effective alt text.
- W3C WAI — Standards-based guidance on the purpose and writing of alternative text.
- Google Search Central: Image SEO Best Practices — Useful for explaining how image metadata and context help Google understand images.
Reviewed by Lucía Marín, Founding editor.