What is alt text?

Alt text is easy to skip because nobody on your team ever notices it is missing. The people who notice are the ones using a screen reader, the ones on a connection too slow to load images, and Google, which reads alt text to work out what a photo shows, one of the small parts of SEO that most sites neglect. The photo at the top of this page is described in its alt as a woman at a built-in oven in a kitchen with dark cabinets; that sentence is exactly what a blind visitor hears.

People say "alt tag", but alt is an attribute of the img element. It has been in HTML since version 2.0 in November 1995, when many people switched images off to save time on dial-up. Today it is the very first rule of the Web Content Accessibility Guidelines (success criterion 1.1.1): every meaningful image needs a text alternative, and purely decorative images get an empty alt so screen readers skip them.

Three versions of one photo

The figure plays the same kitchen photo three ways. Without alt, the screen reader spells out the file name. With a string of keywords, the listener gets nonsense. With a real description, they get the picture.

Common images and how to describe them

Most bad alt text comes from writing it for Google instead of for a person. These are the cases we meet on almost every site we audit:

Three rules follow. Text inside an image, such as a price or a deadline on a banner, belongs in the alt, or a blind visitor misses the offer. An image that is a link describes where it goes, not what it looks like. And never start with "image of": the screen reader announces that already.

The law in the markets you sell to

Alt text stopped being a courtesy some time ago. In the European Union the European Accessibility Act has applied since 28 June 2025 to e-commerce, banking, e-books, transport tickets and other consumer services, and it covers companies outside the EU that sell into it. Micro-enterprises providing services, with fewer than 10 staff and no more than €2 million turnover or balance sheet, are exempt. Whether your site is in scope is answered in does my website have to meet the European Accessibility Act; the full picture is in our European Accessibility Act guide.

In the United Kingdom the Equality Act 2010 obliges service providers to make reasonable adjustments for disabled people, which courts and regulators read as including websites. In the United States, the Department of Justice adopted WCAG 2.1 level AA as the standard for state and local government websites in April 2024, and private businesses face a steady stream of lawsuits under the Americans with Disabilities Act. Missing alt text is the first thing every automated checker reports, which is why it shows up in almost every complaint.

What it costs now, and later

Writing alt text as you upload an image takes half a minute. Fixing it later is a different job: a shop with 500 product photos and no alt text is more than eight hours of work at a minute per photo, before anyone proofreads. So we build it into the publishing step, not the clean-up. On an online store we build, no product goes live without alt text on every photo, which also helps those products in Google Images, a channel often forgotten in ecommerce SEO.

For Google, alt text is one of several signals about an image, alongside the file name, the text around it and its caption. A search term belongs in it when it is true; a list of keywords is what Google itself calls keyword stuffing. How images, titles and structure work together is covered in our guide to technical SEO. To see which images on your own site lack alt text today, run the SEO checker on your home page and your three busiest pages, then turn on VoiceOver or TalkBack on your phone and listen; it also appears as a fixed item in our SEO checklist.