How to write alt text
If you want to know how to write great alt text, you need to know what alt text and image descriptions are, why they matter, and who uses them.
First, let’s get clear on the difference between alt text and image descriptions.
Alt text and image descriptions are both short bits of text added to images.
They describe what’s in the image.
Alt text is vital for people who use screen-readers (normally blind and vision impaired folks). It also helps SEO.
What’s the difference between alt text and image descriptions?
What alt text is
Alt text is short for “alternative text.”
It’s embedded within code on a website or social media, and it’s normally only apparent if you know to look for it.
For example, if you use a screen-reader then you’ll listen to the alt text.
If you’re sighted, you might have to click on “alt” to reveal the alt text.
Alt text is usually short.
It’s good to keep alt text as short as possible, around 125 characters or less.
Some screen-readers cut off alt text at or around 125 characters.
Now for image descriptions.
What image descriptions are
Image descriptions are longer and more detailed.
They’re normally in the main body of a bit of content.
For example, they’re in the actual text of an article, or in the caption of a social media post.
They’re available to everyone: you don’t need to know where to look for them.
Some neurodivergent people (like me) really like them, as they help us check we’ve understood context and meaning. They’re also great for vision impaired people, who might not use a screen-reader.
Why alt text matters
Alt text does several important jobs.
Alt text helps to:
• enhance accessibility by making visual meaning clear for screen-reader users (mainly blind and vision impaired people)
• boost SEO because search engines use alt text to understand image content, which can improve a webpage's search engine rankings,
• improve user experience if, for example, an image doesn’t load properly,
Everyone should include alt text
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 2 million people in the UK are blind or partially sighted. 41% of them use the internet every day.”
Whether you’re posting on social media 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 an image.
Judge based on context and audience.
For example:
If you’re writing the alt text for a blogpost about a fundraising fashion show, users will want to know all about the colour, cut, and style of clothing. But they might not need to know so much about the models’ facial expressions.
If that same photo is a picture of you on your personal website, or a photo announcing a new staff member?
Folks will probably want to know about facial expressions, especially if it suggests something about their character or the tone of the piece of content, like whether someone is 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, “I’m not white. Honestly!”
(There’s a whole conversation to have about “white default” thinking, but that’s for another day…)
To give blind and vision impaired people 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.
Even better, get people to self-describe!
Or, if you can’t ask them to self-describe, but you know how they identify, then you can sometimes use language they’ve used about themselves recently. (Although bear in mind, people can change how they identify at any time, so you might be out of date!)
Explain context
If something has a specific meaning, say it.
Let’s say you’ve shared a graphic of a fist. Is it a random fist, or is it a reference to something specific?
For example, if it’s an echo of the Black power salute, then that’s important and specific information.
If you don’t mention it, they won’t know about that specific history or 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.
You can 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,
some neurodivergent users, as the caption can help them make sense of the image (although they’ll normally read an image description - lots of people don’t know that alt text exists or where to find it),
and everybody (when an image doesn’t load).
Use alt text only to bring that image to life.
Oh and obviously, it’s not for jokes or hidden messages.
Don’t use alt text to add in secret messages, easter eggs, hidden trivia, or loads of keywords (keyword-stuffing for SEO).
Just use it to describe the image!
Include your personality
Alt text must be accurate and focus on relevant details.
But that doesn’t mean it has to be dull.
One of my fave things is reading alt text on pictures people put on the tl. It’s like secret whispered notes. I love knowing what details the author deems important tbh? Just read an alt text on a puppy photo that mentioned how cute his tiny little bottom teeth are 🥺 c’monnnn
— shana (@spacemurmurs) May 31, 2022
Sarah Millican’s alt text is concise, clear and accurate. Oh, and often hilarious.
If you’re sighted, here’s how you can view the alt text on Instagram images.
Don’t start with “a photo of” or “an image of”
Don’t start alt text with “photo of” or “image of.” Screen-readers tell you that it’s an image!
Plus, it 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.
Use AI tools with caution
AI tools are mostly rubbish at alt text.
I haven’t come across any perfectly accurate ones.
But the best are:
Don’t overthink it
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?
It’s important to care about accessible content, but it’s also helpful to keep it simple.
You don’t need to capture every possible detail in every pixel!
You probably don’t need to use up every single character in the character limit.
Focus on purpose
What’s the purpose of the image?
Here’s how I think about it.
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.
It could be a meme, or a photo of a life update.
Is it the “this is fine” meme in response to some world events? Maybe it’s a photo announcing some news, like a picture of the keys to a new home?
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!
Learn more about alt text
Want to learn more about alt text? Check out the resources below:
Accessible Social has excellent 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