Writing good image alt text

This guidance explains how to write alternative (alt) text for images so people can understand images they cannot see.

Only use images when they help people better understand the content or service. Read Before you use images in web content.

Who this guidance is for

This guidance is for people who create and edit web content. It focuses on images used as part of page content.

Images used as part of the website’s interface, such as buttons or navigation, are handled differently and are the responsibility of website developers.

What alt text is and why it matters

Alt text is a short hidden description used for images that contain information. It helps people who use screen readers understand what the image shows and why it matters.

Screen readers read alt text aloud when they reach an image. Alt text will also appear if the image fails to load.

Alt text should not describe every detail. Every image announced by a screen reader demands attention. Unnecessary alt text can slow people down, create noise and make content harder to use.

Instead, explain the point of the image clearly and quickly so people can move on.

When writing alt text, focus on why the image is there. What would someone miss if it was removed?

Focus on what the image means

Alt text is about meaning, not appearance.

People who use screen readers want to focus on the information they need to complete their task. Only include visual detail when it supports that purpose.

There is rarely a single “correct” way to write alt text. What matters is that it makes sense for that page and is quick and easy to understand.

When writing alt text, pause and ask:

Why is this image here on this page?

Your answer is usually what the alt text should communicate.

What good alt text does

Good alt text supports understanding without getting in the way. It helps people move through content efficiently.

Good alt text:

supports how people understand the content
is short and clear
avoids assumptions about gender, emotions, relationships or intent
does not repeat nearby text or captions

How long alt text should be

Alt text is mainly for people using screen readers, so length matters.

In most cases, a single short sentence is enough, usually between 5 and 20 words.

Long descriptions can be hard to follow when read aloud. If more explanation is needed, that detail should be included in the main page content, not hidden in alt text.

Use basic punctuation to support natural pauses when read aloud.

Complex images (charts, maps and diagrams)

If an image includes a lot of detail, such as a chart, map or infographic, a short sentence may not be enough on its own.

In these cases, keep the alt text brief and explain the full information in the page content.

Read Using complex images to learn how to do this.

Images of text

Avoid using images that contain important text. Use real text on the page where possible so it can be read, resized and translated.

Sometimes images of text cannot be avoided. For example, a banner with text may be used as a link that appears across different pages on our website.

These images should still have clear alt text that explains their purpose.

For example, a banner image linking to a page about recycling might include a recycling symbol and a message such as:
“Recycle right. Check if items like batteries, food containers and certain plastics can be recycled at home.”

Good alt text should focus on the main action of the banner and not include every detail. For example:
"Check what you can recycle at home"

With images of text like this:

Do not describe the image itself.
You do not need to copy all the text exactly.
Treat the image like link text and focus on describing its purpose in the alt text.

Decorative images

Some images are included only for visual purposes and do not add any additional meaning.

If removing an image would not change what the page is saying, it is decorative. Decorative images should be skipped by screen readers so people can focus on what matters.

For example, consider a page that listed different organisations and their logos. If their names appeared in the main text, their logos would be decorative. Adding alt text would repeat this information without adding value.

On most web pages, skipping decorative images means using empty alt text. On some platforms, such as Microsoft Word, you may need to manually mark the image as decorative instead.

For guidance on how to do this, read Using decorative images.

One image, different meanings

Alt text should follow the purpose of the page, not describe the image on its own.

Describing everything in an image does not help people understand why it's there.

For example, this image shows a dog standing on the grass in a park.

The image contains other visual details, but most of them do not matter on every page. The page content decides what information matters.

For example:

On a page about assistance dogs, what matters is the function of the harness.
Alt text: “Assistance dog wearing a working harness.”
On a page about parks, what matters is the setting.
Alt text: “Dog standing on grass in a park.”
On a page about animal intelligence, what matters is the type of animal as a general example.
Alt text: “Dog standing on grass.”
On a page about Labradors, what matters is the breed and colour shown.
Alt text: “Yellow Labrador standing on grass.”

In each case, the image is the same, but the purpose of the page changes what matters. Include detail only when it adds meaning in that specific context.

Colour is included in the last example because it explains the variety shown. Other visual details, like background trees or harness colour, are not included because they do not add meaning.

The same is true for images used on our web pages. What may matter most is the service being delivered in the image, not the setting or clothing.

For example, consider an image showing a pothole being repaired.

On a news page, what matters is the event being reported.
Alt text: “Council worker repairing a pothole.”
On a service page about reporting road issues, what matters is helping people recognise the problem.
Alt text: “Pothole being repaired on a residential street.”
On a page explaining how road repairs are carried out, what matters is explaining the process.
Alt text: “Worker filling a pothole with tarmac.”

Using captions with images

A caption is text shown with an image, usually below or above it. Screen readers often announce it with the image.

Captions do not replace alt text. Screen readers use captions and alt text for different purposes. They should support each other, not repeat the same information.

Captions can help explain to everyone why an image matters to the content. Alt text explains what matters about the image for that page.

Alt text should make sense on its own, without relying on a caption.

For example, consider the image of a dog from the previous section:

Caption: "The same image can mean different things depending on the page it appears on."
Alt text: "Dog standing on grass."

Together, the caption, alt text and the surrounding context explain why the image is there and what it is showing.

In this captions section, this image is marked as decorative because it visually repeats and reinforces what is already explained in the text. It would not add anything if announced by a screen reader.

Read more about images that repeat information in Using informative images in content.

A simple way to decide what to write

Before writing alt text, ask yourself:

Why is this image here on this page?
What would be missing if the image could not be seen?
What is the shortest, most neutral way to explain that meaning?

These questions help you make better choices when deciding what to write.

Some tools may generate alt text automatically, but they cannot judge what the image means for the content. Use these questions to review, edit or remove any suggested alt text.

If you are unsure, keep it simple. A short, neutral description is usually best.

Why alt text does not describe everything

Alt text does not replace sight. It replaces the information the image provides for that page.

People who can see an image ignore most visual detail. They focus on what matters based on how it’s used on the page. Alt text needs to do this on purpose.

People who use screen readers can be overwhelmed if alt text tries to describe everything.

Focusing only on what matters keeps content usable. This includes avoiding phrases like “image of” or “photo of” unless they add useful information, as screen readers will already announce them as images.

You can include the type of image if it helps people understand or interpret it. For example:
"CGI illustration of proposed housing development with homes, roads and central green space."

How to check alt text on a live page

Once a page is live, it can be helpful to check how images and alt text work with captions and the wider page context. This is especially useful when reviewing example images or deciding whether an image should be treated as decorative.

You can use browser extensions to help with this.

Image Alt Text Viewer browser extension (Chrome Web Store) shows alt text alongside images so you can check whether it makes sense with the image and surrounding content.

Web Developer browser extension (Chrome Web Store) lets you check the page without images:

Open the extension.
Go to Images.
Select Disable Images.
Refresh the page.

This helps you check whether the page still makes sense without images and whether any important information is missing. When finished, remember to untick Disable Images and refresh the page again.

If the page still works without the image, and the alt text fits the page’s purpose, it is likely doing its job well.

Key points to remember

Alt text is about meaning in context: why is this image here on this page?
The same image can have different alt text on different pages.
Include only the information in the image that matters for that page.
Some images need to be handled differently, such as complex images or images of text.
Decorative images should not have alt text.
Avoid unnecessary detail and assumptions.
Respect screen reader users’ time.

Alt text is not about recreating images. It is about making sure no one misses the point.

Last reviewed: 15 May 2026