alt text

Alt text lives in the alt attribute: <img src="puppy.jpg" alt="Dalmatian puppy playing fetch">. Write what the image shows in plain words, the way you would describe it to someone who cannot see it. Google’s own example ranks a bare alt="puppy" below the descriptive alt="Dalmatian puppy playing fetch", and warns that stuffing the attribute with keywords reads as spam and can work against you.

Match the description to the image’s job

W3C sorts images into cases. Informative images get a short description of the essential information they carry. Functional images (a logo inside a link, an icon button) describe the action, such as alt="Search", not the picture. Purely decorative images take an empty alt="" so screen readers skip them. An empty alt is a deliberate choice, not a forgotten one.

Two common mistakes: do not start with “image of” or “photo of” (the screen reader already announces that it is an image), and do not paste the filename. Read the alt text together with the sentence beside it; if it repeats the copy or breaks the flow, rewrite it.

The same description that helps a blind visitor also feeds machine understanding. Google pairs alt text with computer vision and the surrounding page content to work out what an image is about, which is how pictures surface in Google Images. As AI answer engines read more pages, clear alt text is one more plain-language signal describing visual content they cannot otherwise parse.