Alt text is the words that stand in for an image when the image cannot be seen, whether by a person using a screen reader or by a search engine crawling the page. It is a small attribute with an outsized role in both accessibility and image search.
Why Does Alt Text Matter?
Two reasons. For accessibility, alt text is how people who cannot see images understand what a picture shows, which is both good practice and often a legal requirement. For SEO, it is a primary signal search engines use to interpret an image, which helps it appear in image search and supports the overall relevance of the page. Google's image SEO guidelines describe it as the most important metadata for an image.
How Do You Write Good Alt Text?
Google's own advice is to write useful, information-rich descriptions that use keywords appropriately and fit the context of the page. In practice:
- Describe the image accurately: say what is actually shown, specifically enough to be useful.
- Keep it concise: a short sentence is usually enough; screen readers read the whole thing.
- Add context: describe the image in relation to the page, not in isolation.
- Use keywords naturally: include a relevant term if it fits, but do not stuff keywords, which Google warns against.
- Do not start with image of: screen readers already announce that it is an image.
When Should You Leave Alt Text Empty?
Not every image needs a description. Purely decorative images, such as a background flourish or a spacer, should have an empty alt attribute so screen readers skip them rather than reading noise. The test is whether the image carries information a person needs; if not, an empty alt is correct. Informative and functional images, like product photos and linked icons, always need descriptive alt text.
What Are Common Alt Text Mistakes?
The usual errors are leaving alt text off informative images entirely, stuffing it with keywords in a way that helps neither users nor search engines, using the same generic text on every image, and describing decorative images that should be skipped. Alt text works best when it is written for a person who cannot see the image, which also happens to satisfy search engines.
Frequently asked questions
What is alt text used for?+
Alt text describes an image so screen readers can read it aloud for people who cannot see it, and so search engines can understand the image. It serves accessibility first and also helps images appear in image search.
How do you write good alt text?+
Describe the image accurately and concisely, add context relevant to the page, and include a keyword only if it fits naturally. Google advises useful, information-rich text without keyword stuffing, and you should not begin with the words image of.
Does alt text help SEO?+
Yes. Alt text is a primary signal search engines use to understand an image, which supports image search and page relevance. Its first purpose is accessibility, but writing it well benefits both users and search.