Alt text on Threads: get it right before you post

Threads has a built-in field for alt text on photos and videos, and the safest time to fill it in is before you post. On a computer, Meta’s help center says to attach the photo or video, click More at its bottom left, choose Add alt text, type your description, and click Done. The Threads apps have the same option, though the layout may differ, so check the attachment itself rather than relying on a screenshot.

The reason to do it first is that the edit window is narrow. Meta says you can edit a Threads post for 15 minutes, and that only the text can be changed; attachments cannot be added or removed. Meta’s alt text page describes adding and editing a description before you post, and we could not find a documented way to change it afterward. Treat the field as one chance, and check the current behavior in the app if a post has already gone out.

What to write in the field

Describe what the image shows and why it is there. The W3C’s guidance on informative images is to convey the meaning of the image concisely, and to avoid repeating what the nearby text already says. On Threads that matters, because the post text sits right above the photo. If your post says “Our new patio is open,” the image description should add what a listener cannot get from that sentence.

The help pages we read do not state a character limit, so write what a listener needs and stop. For a rule of thumb on length, see the 125-character rule.

Make it part of the posting routine

Because the alt text goes in before the post goes out, it belongs in your drafting step, not your cleanup step. Write the description when you pick the photo, the same way you would write the caption. Anyone on a screen reader hears it where the image would be; for what that sounds like, see how screen readers announce images.

If you run the same photo across networks, the habit carries over. The fields live in different places, as in Instagram’s Advanced Settings, but the description you write is largely reusable. One caution for teams that schedule Meta posts: the field was removed from Meta Business Suite, so check where your own tool lets you add it.

For a stack of images, take a screenshot of each, run SnipAlt with Ctrl+Shift+A (⌘⇧A on a Mac), edit the draft, and paste it into the field before you post. If you are building the habit across a team, why alt text matters is a good place to start the conversation.