What Is Alt Text?

How Alt Text Works

Alt text lives in one place: the alt attribute of an HTML <img> element. In <img src="puppy.jpg" alt="Dalmatian puppy playing fetch">, the words after alt= are the alt text. That short string does three separate jobs, and its value comes from serving all three at once.

First, accessibility. A screen reader can’t interpret a photo, so when it reaches an image it reads the alt text aloud. For a visually impaired user, the alt text is the image. Google’s own SEO starter guide frames it exactly this way: alt text is “a short, but descriptive piece of text that explains the relationship between the image and your content.”

Second, fallback. When an image fails to load — a broken path, a blocked host, a slow connection that times out — the browser displays the alt text in the image’s place. A reader who never sees the picture still gets the meaning.

Third, search. A search engine can analyze pixels, but a human-written description is far more reliable. Google states plainly that the alt attribute is “the most important attribute when it comes to providing more metadata” for an image. It’s the main thing that decides how your image is understood in image search.

There’s a fourth, quieter role. When an image is wrapped in a link, Google uses its alt text as the anchor text for that link. So on a linked image the alt attribute describes the picture and labels the link destination simultaneously.

Writing Good Alt Text

Google’s guidance is short: write “useful, information-rich content that uses keywords appropriately and is in context,” and don’t stuff the attribute with keywords, because that “results in a negative user experience” and can look like spam.

• Describe the meaningful content. State what the image actually shows and why it’s on the page — the subject, the action, the relevant detail.
• Be concise. A phrase or short sentence. Google’s model example is just “Dalmatian puppy playing fetch.”
• Use keywords only where they fit naturally. If the image genuinely depicts your topic, the description will include the relevant words on its own.
• Empty alt for decorative images. A spacer or purely ornamental graphic should use alt="" so screen readers skip it rather than announcing noise.

Example of Alt Text

Google’s image documentation supplies a direct, worked contrast, which makes it the cleanest real example to learn from. For a photo of a puppy, Google gives the recommended alt text as Dalmatian puppy playing fetch — four words that name the subject, the action, and the specific breed. It’s accurate, it’s concise, and any keywords it contains (“puppy”) are there because they truly describe the image.

Google then shows the failure mode on the same image: an alt attribute stuffed with repeated variations like “puppy dog baby dog pup pups puppies doggies…” That version helps no one. A screen-reader user hears a meaningless string; a reader on a broken connection sees gibberish where the image should be; and a search engine that has learned to detect stuffed attributes reads it as manipulation rather than description. Google explicitly labels the stuffed version as bad practice that “results in a negative user experience.”

The third case Google names is the most common of all: no alt text at all, which leaves the image undescribed for accessibility, fallback, and search alike. Line the three up — the missing case, the stuffed case, and the concise “Dalmatian puppy playing fetch” — and the rule writes itself. Describe the image honestly and briefly, the way you’d narrate the page to someone who can’t see the screen. That single instinct produces alt text that serves accessibility and image SEO at the same time, which is exactly what Google is asking for.

Frequently Asked Questions

The Bottom Line

Alt text is the description you attach to an image so that people who can’t see it, and machines that can’t interpret it visually, both understand what it shows. Write it as a genuine, concise description of the image in its context — the way you’d narrate the page to someone over the phone — and you satisfy accessibility, image search, and the link signal all at once. Skip it or stuff it, and you lose all three.