How to write great alt text

Alt text is the text alternative that describes an image. It shows up if an image doesn’t load, whether because of slow internet connections or because a user has turned images off to save data. And it’s the main way for blind and low vision users to perceive images.

 

If you think you don’t need alt text on your images, think again. As Becky Brynolf, Head of Social Media at The Royal National Institute of Blind People, says: “An estimated two million people in the UK are blind or partially sighted. 41% of them use the internet every day.”

 

Whether you’re tweeting, posting an image on Instagram, or writing a blogpost, alt text provides crucial context.

 

Here are some practical tips to make your alt text useful and useable.

 

 

Keep it short

 

Capture the relevant details but try not to slow users down with elaborate descriptions. Around 125 characters is often a good length. But remember that accuracy is more important than conciseness. So take as long as you need to capture the important details.

 

 

Focus on what matters

 

You don’t need to describe everything in the image. Judge based on the context and the audience for your content. If you’re writing the alt text for a blogpost about a fundraising fashion show, users are likely to want to know all about the colour, cut, and style of clothing. But they might not need to know about the models’ facial expressions.

 

If you’re writing the alt text on a photograph of your charity’s new CEO, uesrs may want to know details about their appearance, like hair colour, type length, and skin colour. They might also want to know about their expression, especially if it suggests something about their character, like whether they’re grinning warmly or looking solemn.

 

 

Talk about minoritised identities

 

If we don’t mention someone’s race, many of us assume that people are white, as Haben Girma explains in her video about the need to mention race, which you can view below.

 

 

To give blind and low vision users access to the same information as sighted people, it’s also important to include details about gender presentation. You can describe someone’s gender presentation, without assuming their gender. Consider describing features like their hair length and style, clothing, or makeup instead.

 

 

 

Convey function

 

If something has a known meaning, say it. Blind users need to know that the graphic of a bright blue bird on your website is the Twitter icon, or they won’t know they can select it to visit Twitter.

 

Low vision people might need to know that the raised fist in your graphic is the Black power salute, otherwise they’ll miss out on important context.

 

 

Skip alt text on decorative images

 

Decorative images are often used to break up long chunks of text. They’re particularly common in research reports, policy updates, and technical explainers.

 

If an image is purely decorative, then don’t waste the time of your users by adding alt text. Mark it as decorative so that screen readers will skip it.

 

 

Leave out credits or copyright information

 

Alt text is not a caption. It’s a description of the visual appearance of an image. Keep in mind that the alt text is for blind and low vision users who won’t see the image. It’s also very useful for some neurodivergent users, as the caption can help them make sense of the image.

 

Use alt text only to bring that image to life. It’s not for jokes or hidden messages.

 

 

Include your personality

 

Alt text must be accurate and focus on relevant details. But that doesn’t mean it has to be dull!

 

Sarah Millican’s alt text is concise, clear and accurate. Oh, and it’s hilarious. 

 

If it’s appropriate for your charity and tone of voice, show the full range of your personality.

 

 

Don’t start with “a photo of” or “an image of”

 

Don’t start alt text with “photo of” or “image of” because this can get repetitive and irritating for screen reader users.  If an image is in an unusual medium, for example, you’re tweeting a photograph of an oil painting or collage, then specify that it’s an oil painting or collage.

 

 

Don’t overthink it

 

Lastly, it’s easy to get tangled up in overthinking: what’s an important detail? Who is my audience? What if I give too much information for one user and not enough for another?

 

Try this rule of thumb. Imagine you’re describing an image to a friend or a relative. Maybe you’ve messaged them the image, but it hasn’t loaded properly.

 

You want to mention it because it’s relevant to a story you’re telling, because it’s funny or relatable.

 

You explain it to them briefly, in simple language. You focus on what’s relevant for the purposes of your story. You describe it, without fussiness or dull detail. Congratulations, you’ve just written a fantastic bit of alt text.

 

Want to learn a little more about alt text? Check out the resources below:

• Accessible Social has detailed guidance on how to write quality alt text
• Dr Amy Kavanagh shares many useful accessibility resources like her thread on tips for writing alt text (see below)
• Holly Tuke has a range of resources on alt text and accessibility, including 6 ways to make your social media posts accessible for people with a visual impairment
• RNIB’s Guide to Accessible Social Media has an overview of the accessibility features and benefits of different social media platforms, including Twitter, Instagram, TikTok and LinkedIn