What alt text does
The W3C is the group that sets web standards. Its accessibility pages say images need a text alternative that carries the same information or job as the image. They add that this text can be read aloud or shown in Braille. Google's image guide calls alt text the most important piece of metadata for an image. Metadata is extra information about a file. Google also says alt text helps accessibility.
Good and bad examples
Google's image guide gives a ladder for a photo of a dog:
- Bad: no alt text at all, or a long list of keywords.
- Better: alt text that says puppy.
- Good: alt text that says Dalmatian puppy playing fetch.
Google says to avoid filling alt text with keywords. Keyword stuffing makes for a poor experience, and Google says it may make your site look like spam.
A made-up example
A tile shop in Jaipur puts a photo of a grey bathroom wall tile on a product page. The file is called IMG00023.JPG, and the alt text is empty.
A better version uses a file name such as grey-matte-bathroom-wall-tile.jpg and alt text such as Grey matte wall tile, 30 by 60 centimetres, fitted in a bathroom. Google says file names should be short but descriptive. It gives my-new-black-kitten.jpg as better than IMG00023.JPG.
Images that need different treatment
- Decoration only: the W3C says to use an empty alt, written as alt with two quote marks and nothing inside, when the image adds no meaning.
- Images that are links: describe where the link goes or what it does. Google also uses the alt text of a linked image as its anchor text. See anchor text.
- Charts and dense data: the W3C says to put the information elsewhere on the page instead of squeezing it into alt text.
- Text inside an image: repeat the same words in the alt text. The W3C also says to avoid putting text in images unless it is a logo.
The W3C adds that the right alt text depends on how and where the image is used. The same photo can need different words on two pages.
Common mistakes
- Leaving alt text out because the picture is obvious to you.
- Writing a keyword list instead of a description.
- Starting with the words image of or picture of. The reader already knows it is a picture.
- Using file names such as image1.jpg or 1.jpg, which Google says to avoid.
Related terms
- Anchor text: the visible words of a link.
- On-page SEO (search engine optimisation): the work you do on the page itself.
- Technical SEO: the setup work that lets search engines read your site.
- Core Web Vitals: Google's page experience measures, which images can affect.
Alt text is one small part of on-page SEO. If you want a full check of your pages, see our SEO audit service.
Sources
- Google Search Central, "Google Images SEO best practices" (developers.google.com/search/docs/appearance/google-images), read 9 October 2026.
- Google Search Central, SEO Starter Guide (developers.google.com/search/docs/fundamentals/seo-starter-guide), read 9 October 2026.
- W3C Web Accessibility Initiative, "Images Tutorial" (w3.org/WAI/tutorials/images/) and "Images Decision Tree" (w3.org/WAI/tutorials/images/decision-tree/), read 9 October 2026.
- Google Search Central, "Link best practices for Google" (developers.google.com/search/docs/crawling-indexing/links-crawlable), read 9 October 2026.
