Alt Tags SEO
Describes an image with HTML text that helps search engines and screen readers understand its content when the image cannot be seen.
If you have ever stuffed keywords into alt text hoping for a ranking boost, you already know Google penalises keyword stuffing rather than rewarding it.
Key points
- Write alt text that describes the image naturally, not a list of keywords.
- Use unique alt text for each image; this is a core alt text seo practice.
- Leave alt attribute blank for decorative images that add no information.
- Rename image files descriptively before uploading; image filename also matters for SEO.
- Keep alt text concise, typically under 125 characters, but no hard limit.
Three alt texts, one product page, very different outcomes
A product page lists three images of the same running shoe. Image A has alt text 'image', image B has 'cheap running shoes buy online', image C has 'red Nike Air Zoom Pegasus on a track'. After indexing, only image C appears in Google Images for relevant queries, while image B is ignored due to keyword stuffing and image A provides no context.
Three ways alt text supports SEO
- Image search visibility Alt attribute seo helps your images appear in Google Images search results, driving additional traffic when descriptions are natural and relevant.
- Topical relevance Search engines use alt text alongside page content to understand the overall topic of a page, reinforcing the page's subject.
- Accessibility compliance Alt text is required by WCAG for accessibility, and accessible sites tend to perform better in search as a side effect of better user experience.
Four common mistakes with alt text
- Keyword stuffing Filling alt text with keywords instead of describing the image naturally hurts readability for both users and search engines and can trigger spam penalties.
- Blank alt on meaningful images Lack of alt text on informative images loses context for search engines and screen readers, missing opportunities for image search traffic.
- Vague descriptions Using 'image' or 'photo' as alt text provides no value; be specific about what the image shows and its function on the page.
- Repeating the same alt text Using identical alt text for multiple different images creates duplicate content issues and reduces the relevance signal for each image.
Three situations where alt text matters most
- Product images Product images benefit from detailed alt text that acts as an seo tag for the item, describing features, colours, and sizes for both search and accessibility.
- Infographics and charts Complex images need detailed alt text to convey data that cannot be seen by screen readers, ensuring the information is accessible to all users.
- Images as links When an image is a link, its alt text should describe the destination, not the image itself, so screen readers know where the link goes.
Common questions
What is alt text for images?
Alt text is a text description added to an image in HTML, used by screen readers and search engines to understand the image.
How to write alt text for images?
Describe the image concisely and specifically, focusing on its content and context. Include relevant keywords naturally if they fit.
What are alt text best practices?
Keep alt text under 125 characters, unique per image, descriptive, and avoid keyword stuffing. Use empty alt for decorative images.
Sources
- Google Search Central Official guidance on alt text for image search
- W3C Web Accessibility Initiative Tutorial on alt text for accessibility