Alt text on Bluesky

Alt text is the description of an image that people who cannot see it read instead. On Bluesky it is easy to add, widely expected, and easy to forget.

Updated 30 September 2026

What alt text is for

A screen reader reads a post aloud. When it reaches an image it reads the alt text, or, if there is none, says "image" and moves on. For a blind or partially sighted reader that is the difference between getting the joke and hearing that there was one. Alt text also shows when an image fails to load, and it is what any tool that indexes images has to go on.

On Bluesky it matters more than on most networks because the culture expects it. Many of Bluesky's early users came from communities where alt text was the norm, and it still is: people reply asking for it, custom feeds exist that show only posts with alt text, and accounts that never add it get quietly filtered out.

How to add it

1. Attach the image in the composer. An ALT button appears on the image.
2. Tap it and write the description. Bluesky's limit is far longer than the post's 300 characters.
3. Save. The image shows a small ALT badge once it has text, and readers can tap the badge to read it.
4. In Settings, under Accessibility, turn on Require alt text before posting, so that the composer refuses a bare image from now on.

If you post through Updrift's Planner, the composer asks for alt text on each image as you attach it and keeps it with the image, so a post written on Monday and sent on Thursday goes out with its description.

How to write it

Say what the image shows, in the order someone's eye would take it in, in plain words. Two or three sentences is usually right. Some rules of thumb that hold up:

• Start with the subject. "A grey cat asleep on a stack of paperbacks" beats "This is a photo I took yesterday of my cat".
• Leave out "image of" and "photo of". The screen reader already says it is an image.
• Include any text that is in the image. A screenshot of a post, a poster, a sign: transcribe the words, or the reader gets nothing.
• For a chart, give the finding, not the axes. "Followers by hour: highest at 20:00, lowest at 04:00" is what a sighted reader takes from it.
• Describe what matters for the post. The same photo of a street needs different alt text under "look at this shopfront" and under "look at this sky".
• Leave the joke in. If the image is funny, the alt text should be too. Describing the punchline is not spoiling it; it is delivering it.
• Do not repeat the post. The alt text is read after the post, so a copy of the post's text tells the reader nothing new.

What alt text is not

It is not a caption. A caption adds context the sighted reader also gets; alt text replaces what they see. It is not a place for hashtags or keywords: Bluesky search does not treat alt text as tags, and a reader hearing "#art #artist #illustration" has been given nothing. And it is not optional for text in images. A screenshot of a long post with alt text of "screenshot" has shut everyone who cannot see it out of the whole point of the post.

Images, alt text and your figures

In Updrift's own figures, posts carrying an image beat the account's usual post more often than text-only posts do. That is measured across many accounts, and it says what went with better posts rather than what caused them. But an image only reaches everyone when everyone can read it, and alt text is the part of that you control.

The What works report groups your own posts by format, so you can see how your posts with images do against your usual. The top line of the report is free for one account; the full report comes with a paid plan.

Going back over old posts

Bluesky posts cannot be edited, so alt text cannot be added to an image after the post has gone out. For a post that matters, the honest fix is to reply to it with the description, which screen readers reach in the thread. For everything from now on, the setting above is the fix: turn it on and the problem does not come back.