- Alt text is for people first: screen readers read it aloud, and browsers show it when the image fails to load.
- Google uses alt text together with the page text, the file name and computer vision to understand an image, so describe what the image actually shows.
- Write a short, specific description: no keyword lists, no "image of", and no paragraphs.
- Give purely decorative images an empty
alt=""; never leave the attribute out, or screen readers may read the file name. - On a linked image, the alt text acts as the anchor text, so describe where the link goes.
What is image alt text?
Alt text is the text in an image's alt attribute: a short description that stands in for the picture when someone cannot see it.
It sits inside the <img> tag in your HTML:
<img src="/images/red-trail-running-shoe.webp" alt="Red trail running shoe with a thick grey sole, side view" width="800" height="600">The main job of alt text is accessibility. Screen readers read it aloud to blind and low-vision visitors, and browsers show it in place of an image that fails to load. Whether an image needs alt text, and what it should say, depends on what the image does on the page: does it carry information, is it a link or button, or is it decoration? The W3C Web Accessibility Initiative's alt decision tree walks through those questions one at a time and is the best quick reference when you are unsure.
How does Google use alt text?
Google reads alt text together with computer vision, the text around the image and the image file name to work out what an image shows and which searches it fits.
Google's image SEO best practices say the alt attribute is the most important attribute for giving Google metadata about an image, and that Google uses it along with computer vision and the contents of the page. In practice that means three things work together:
- Alt text. A useful, information-rich description that uses keywords where they fit naturally and matches the content of the page.
- Surrounding text. Captions, headings and the paragraph next to the image give context. Place images near the text they relate to.
- File name. Google notes that the file name can give it clues about the subject, so
red-trail-running-shoe.webphelps more thanIMG00023.webp.
The same Google page warns against filling alt attributes with keywords, because it makes the page look spammy and gives a poor experience. Good alt text helps the image appear in Google Images and gives the page itself a little more relevant context.
How does Bing use alt text?
Bing also reads alt text, titles and file names to understand images, and its guidelines ask for descriptive, relevant text around them.
The Bing Webmaster Guidelines advise using descriptive alt text and file names for images, placing images near related text, and avoiding keyword stuffing. The advice lines up with Google's: describe the image honestly for a person, and both search engines can use it. To see how Bing is indexing your pages, set up Bing Webmaster Tools.
Good vs bad alt text examples
Good alt text is short, specific and describes what the image shows in the context of the page.
Alt text for a product photo of a red trail running shoe
| Type | Alt text | Why |
|---|---|---|
| Empty on an informative image | alt="" | Screen readers skip the image and search engines learn nothing. Empty alt is only for decoration. |
| Keyword-stuffed | alt="shoes running shoes trail shoes best shoes buy shoes cheap" | Reads as spam to people and to Google, and describes nothing. |
| "Image of…" | alt="Image of a shoe" | Screen readers already announce that it is an image, and "a shoe" is too vague. |
| Too long | alt="This is a photo we took in our studio last spring showing our newest red trail running shoe, which has a grey sole, reflective laces, a breathable upper and…" | A paragraph is tiring to listen to. Put the detail in the visible text or a caption. |
| Good | alt="Red trail running shoe with a thick grey sole, side view" | Short, specific, matches the page and uses the natural keyword once. |
A simple test: if you read the page aloud to someone over the phone, what would you say about the image? That sentence is usually the right alt text. Skip words like "photo of" unless the medium matters (for example "oil painting of a harbour at dusk").
Decorative images: use alt="" and never leave the attribute out
Images that only decorate the page should have an empty alt attribute, alt="", so screen readers skip them.
Background flourishes, divider lines and stock photos that add no information are decorative. The W3C WAI tutorial on decorative images recommends a null (empty) alt value for them. An image that sits next to text which already says the same thing, such as an icon beside the word "Phone", can usually be treated the same way.
Leaving the attribute out is not the same thing. When an <img> has no alt attribute at all, many screen readers read the file name instead ("IMG underscore 4 0 2 3 dot webp"), which is worse than silence. Always include alt: with a description for meaningful images, and empty for decoration.
<!-- Decorative: skipped by screen readers -->
<img src="/images/wave-divider.svg" alt="">
<!-- Missing attribute: avoid -->
<img src="/images/wave-divider.svg">Alt text on linked images works as anchor text
When an image is the only content of a link, its alt text is the link's anchor text, so it should describe where the link goes.
Google's image guidelines note that alt text is useful as anchor text when you use an image as a link. A logo that links to the home page should say something like alt="MrKeyword home", not alt="logo", and a linked "Download the report" banner should use those words. An image link with no alt text is a link with no words at all, for search engines and for screen reader users.
<a href="/pricing"><img src="/images/plans-banner.webp" alt="See MrKeyword pricing plans"></a>How to find images with missing alt text
Paste a URL into the free on-page SEO checker: it counts the images on the page and warns when any of them have no alt attribute.
Run the on-page SEO checker
The report includes a warning such as "2 of 4 images have no alt text" when images have no
altattribute at all. Images with an intentional emptyalt=""are not flagged, because that is the correct markup for decoration.Find the exact images in DevTools
Open the page in Chrome or Edge, press F12, go to the Console and run
document.querySelectorAll('img:not([alt])'). It lists every image with no alt attribute so you can find each one in your template or CMS.Review the empty ones too
Run
document.querySelectorAll('img[alt=""]')and check that each result really is decorative. A product photo or chart withalt=""needs a real description.
Alt text is one item on a longer list. Work through the rest of the page with our on-page SEO checklist, and remember that the image shown when a page is shared on social apps has its own alt field, covered in our guide to Open Graph tags.
Questions and answers
Image alt text questions
What is alt text?
Alt text is the text in an image's alt attribute. Screen readers read it aloud, browsers show it when the image fails to load, and search engines use it to understand the image.
Does alt text help SEO?
Yes. Google uses alt text together with the page text, the file name and computer vision to understand images, which helps them appear in Google Images and adds context to the page.
How long should alt text be?
Keep it to a short phrase or sentence that describes what matters in the image. Put longer detail in a caption or the visible text.
What alt text should a decorative image have?
Use an empty alt attribute, alt="". Screen readers then skip the image. Do not leave the attribute out, or the file name may be read aloud.
Should I start alt text with 'image of'?
No. Screen readers already announce that it is an image. Start with what the image shows.
How do I find images with missing alt text?
Run the free on-page SEO checker on a URL. It warns when images have no alt attribute. In browser DevTools, document.querySelectorAll('img:not([alt])') lists them.
Sources
- Google Images SEO best practices — Google Search Central: alt text, file names, surrounding text and linked images
- An alt decision tree — W3C Web Accessibility Initiative: how to decide what alt text an image needs
- Decorative images — W3C Web Accessibility Initiative: when and how to use an empty alt attribute
- Bing Webmaster Guidelines — Microsoft Bing: guidance on content, images and alt text
