A screenshot is usually shared for its words. Someone posts a screenshot of a post, a message thread, an error or a news headline because they want you to read it. For a screen reader user, the alt text is the only way to read it, so the usual advice to "describe the image" is not quite right. For most screenshots, the job is to pass on the text, plus enough about the layout to make sense of it.
Start by asking what the screenshot is for
The same screenshot can need different alt text depending on why you are sharing it. Decide which of these it is before you write:
- To share what someone said. A screenshot of a post, a comment or a message. The words and who wrote them are what matter.
- To show how something looks or works. An app screen, a settings page, an error message, a design. The relevant part of the interface matters, not every label on it.
- To quote a longer text. An article, a policy, a page of a book. A summary and the key lines matter.
The W3C's tutorial on images of text puts the rule simply: when an image shows text that is meant to be read, the text alternative must contain the same text. The Nielsen Norman Group's guidance on alt text adds the practical limit: quote short text exactly when it is an important part of the image's message, and summarise when it would not fit.
Name it as a screenshot
Normally you skip "Image of" because the screen reader already announces an image. Screenshots are an exception worth making. Starting with "Screenshot of a post by..." or "Screenshot of an error message..." tells the listener at once that what follows is a transcription, not a description of a scene. The W3C notes that naming the type is fine when it helps, and this is one of those cases.
Screenshots of posts and comments
Give the source, then the words, then anything else visible that changes the meaning.
- Weak: "Screenshot of a tweet."
- Good: "Screenshot of a post by @cityparks: 'The Riverside playground reopens on Saturday at 9am. The splash pad stays closed until the new pump arrives.' Posted 14 October, with 2,300 likes."
Include the handle or name when it matters who said it, which is usually the reason to share a screenshot in the first place. Include counts, dates or a "verified" badge only when they are part of your point. If the post has an image of its own, describe it in a short sentence after the text.
If you have hidden someone's name or handle in the image, do not write it in the alt text. The alt text should never reveal more than the image does.
Screenshots of message threads
Conversations need the order and the speaker for each message, or they turn into a jumble.
- Weak: "Screenshot of a funny text conversation."
- Good: "Screenshot of a text conversation. Mum: 'What time are you home?' Me: 'About 7.' Mum: 'Ok I'll make lasagne.' Mum, a minute later: 'Lasagne cancelled, the oven is broken.'"
Use the names as they appear on screen, or "Me" and the other person's label if the names are hidden. Leave out timestamps and read receipts unless the joke or the point depends on them, as it does in the last line above.
Screenshots of apps, websites and errors
When the screenshot shows an interface, describe the part that matters and quote the text a reader needs.
- Weak: "Screenshot of the settings page."
- Good: "Screenshot of the Bluesky accessibility settings. The switch for 'Require alt text before posting' is turned on."
For an error, the exact message is the most useful part, because readers may search for it:
- Good: "Screenshot of an error dialog in a photo editor: 'Export failed. The file is larger than 2 GB.' A single button reads 'OK'."
You do not need to read out every menu item, icon and label on the screen. If someone needs that level of detail, a screenshot was probably not the best format, and a written list of steps would serve everyone better.
Screenshots of long text
Articles, policies and long posts often run past what fits comfortably in alt text, or past the platform's limit. Several approaches work:
- Summarise and quote the key lines. "Screenshot of a news article headlined 'Council approves new cycle lanes'. The highlighted paragraph reads: 'Work on the first two routes will start in March and take about six months.'"
- Put the text somewhere else. Paste the full text in the post, in a reply, or link to the original, and say in the alt text where it is: "Full text in the first reply."
- Use the limit you have. Bluesky allows 2,000 characters and X allows 1,000 per image. Mastodon's limit depends on the server. The alt text character limits post lists each one with its source.
Whichever you choose, keep the most important line first. The guide on how long alt text should be explains why the start matters most.
Transcribe carefully
A transcription that is almost right can be worse than a summary, because the reader trusts it. A few habits help:
- Copy, do not retype, when you can. If the original text is available, copy it from there. Mastodon's web interface has an Add text from image button in the description dialog that pulls the text out of the image for you to check.
- Keep spelling and wording as shown. If the original has a typo that matters, keep it and, if needed, mark it with "[sic]".
- Keep the original language. Quote text in the language it appears in, rather than translating it silently.
- Describe emoji when they carry meaning. "Followed by a crying-laughing emoji" tells the listener what the writer meant to show.
- Check numbers twice. Prices, dates and times are where small slips change the meaning.
Consider not using a screenshot at all
The W3C's guidance on images of text asks websites to use real text instead of pictures of text where possible, because people cannot adjust how text in an image looks, such as its size or colours. On social media that is not always practical, but it is often possible: quote the post or share a link to it, paste the error message as text, or write the steps out. When you do use a screenshot, the alt text is what makes it readable for everyone who cannot see it.
Screenshots with AltKit
Screenshots are where alt text takes the longest to write by hand. AltKit's alt text quotes meaningful text exactly, in its original language, and can run longer for a text-heavy image while staying under 1,000 characters. In the browser extension, the Create Alt Text button sits in the alt text dialog on Bluesky, X, Mastodon and the other supported sites, so the transcription lands in the field for you to check. As with any transcription, read it against the screenshot before you post.
For where to find the alt text field on each platform, see how to add alt text on social media.