How to write image alt text for SEO and accessibility

What is alt text and why does it matter?

Alt text, short for alternative text, is the text in an image's alt attribute. It stands in for the image wherever the image cannot be seen.

It serves people first. Blind and low-vision visitors using screen readers hear the alt text in place of the image. Providing a text alternative for meaningful images is a Level A requirement of the Web Content Accessibility Guidelines, under success criterion 1.1.1, Non-text Content.

It also serves search engines. Google's image SEO guidance says it uses alt text, together with computer vision and the page's content, to understand what an image shows. That helps the image appear in Google Images and gives context to the page around it. When an image is a link, its alt text works like the link's anchor text.

How to write good alt text

Ask what the image adds to the page, then write the words that would replace it if it were gone.

1. Describe what matters in the image for this page. A product photo needs the product, color and model; the same photo in a style article might need the outfit instead.
2. Be specific. Golden retriever puppy chewing a red rope toy says more than dog.
3. Skip phrases like image of or picture of. Screen readers already announce that it is an image.
4. For a linked image or an image button, describe the action or destination, such as Download the price list, rather than the picture.
5. For an image that contains text, such as a banner or a quote card, include that text in the alt.
6. For charts and diagrams, give the key takeaway in the alt and put the full data or explanation in the surrounding text.

When should alt text be empty?

Decorative images add nothing to the meaning of the page: background flourishes, spacer graphics, or a photo whose content is already fully described in the text next to it. Give these an empty alt attribute, written as alt with nothing between the quotes.

An empty alt tells screen readers to skip the image. That is different from leaving the attribute out altogether. When alt is missing, many screen readers fall back to reading the file name, which can mean hearing something like IMG underscore 4032 dot jpg.

If the same information is already in a caption or link text right beside the image, an empty alt also avoids having it read twice.

How long should alt text be, and should it include keywords?

There is no official length limit. A common rule of thumb is to keep alt text under about 125 characters, usually a single sentence or less. If an image needs more explanation than that, put the detail in a caption or the body text.

Keywords are fine when they genuinely describe the image. Keyword stuffing is not. Google's guidance warns that filling alt attributes with keywords creates a poor experience and can cause a site to be seen as spam. A list of search phrases is also useless to someone using a screen reader.

• Good: Stainless steel French press with bamboo lid on a kitchen counter.
• Too vague: Coffee maker.
• Stuffed: French press coffee maker best French press buy French press online cheap.

How to find images with missing alt text

Start with free tools. Lighthouse in Chrome DevTools runs an accessibility audit that flags image elements without alt attributes, and browser extensions such as WAVE highlight them on the page. A site crawler can list every image missing alt text across many pages at once.

Then decide for each image: does it need a description, or is it decorative and should get an empty alt? An automated check can find a missing attribute, but only a person, or a careful review, can judge whether the description is right.

Where SEOAmazing fits

SEOAmazing's crawl snapshots images missing alt text on each page, alongside titles, meta descriptions, headings and structured data. Its AI proposes alt text for those images, showing the current value, the proposed value, a severity and a one-line rationale. You can edit each suggestion, and nothing changes until you approve it.

Approved alt text is applied by the SEOAmazing pixel, one script line in your site's head, so you do not have to edit images one by one in your CMS. Google renders JavaScript and can see the change. It stays live while the snippet is installed; if you remove the snippet, the pages revert to their original markup.

Frequently asked questions