What is alt text and how do I write it?

Alt text is the alt attribute on an image tag: a short written description of what the picture shows or does. Screen readers read it aloud, browsers show it when the image fails to load, and search engines use it to understand the image. Write what a person needs to know, in plain words, usually under a sentence long.

Why it matters

People who are blind or have low vision rely on alt text to know what an image adds. Without it, a screen reader may read out a file name instead. Search engines also use alt text, along with the surrounding text, to understand an image, so it supports image search too.

How to write it

Ask what the image is for. A photo that supports the story needs a description. A button icon needs the action it performs, such as "Search".
Describe the useful content in plain language: "Owner arranging bread on a bakery shelf".
Keep it short. One brief sentence or phrase is usually enough, and there is no need to start with "image of" or "picture of".
If the image contains text, include that text.
If the image is purely decoration, use an empty attribute so screen readers skip it:

<img src="/images/loaf.jpg" alt="Sourdough loaf cut open on a wooden board">
<img src="/images/divider.png" alt="">

For an image inside a link, describe where the link goes, not the picture. For a chart, give the main finding in alt text or in the text nearby.

An empty alt="" is correct for decorative images. A missing alt attribute is different: it is an error, and screen readers may read the file name instead.

Common mistakes

Leaving the attribute out completely.
Stuffing keywords into the description.
Repeating the file name, such as "IMG_2041.jpg".
Writing a long paragraph where a short phrase would do.
Putting important text in an image and not repeating it anywhere else on the page.

Crawvix's scan checks that images have alt text, and Crawvix Image Doctor lists every image on a scanned site with findings for missing alt text, broken images and heavy files.

Frequently asked questions

Is alt text the same as the title attribute?

No. The title attribute shows as a tooltip on some devices and is not a dependable replacement. Alt text is what assistive technology reads.

How long should alt text be?

There is no fixed limit. A short phrase or one sentence is usually enough, and long descriptions belong in the page text.

Does alt text help SEO?

It helps search engines understand an image, especially in image search. Write for the reader first and let the keywords follow naturally.

To see which images on your site lack alt text, Try the free website sample.