Alt text on X: the 1,000-character field almost nobody fills in

X gives you 1,000 characters to describe an image. That's eight times the 125-character rule of thumb most marketers work from, and considerably more room than Instagram, Facebook, or LinkedIn hand you. It sits behind a small button on every image you upload, and on most accounts it stays empty.

The size of that field is a hint about what X expects from you. It's also a trap if you take it literally.

Where the button actually is

On the web, upload your image and click Add description underneath it, type into the box, then click Save. On iOS and Android it's a small +ALT badge in the corner of the uploaded image — tap it, write, tap Done. Either way the badge drops its plus sign once there's text behind it, which is the quickest way to check your own work before you press post.

If you attached four images, you have four descriptions to write. On mobile the images sit in a horizontal scroll, each carrying its own +ALT badge. On the web, the description dialog has previous and next arrows so you can move through the set without closing it. Nothing carries over — what you wrote for image one doesn't apply to image two.

What to do with 1,000 characters

Not fill them. The limit is generous because some images genuinely need the room: a dense chart, a screenshot of a full page of text, a photo where the small details are the whole point. Most images aren't that. A screen reader reads your description aloud, start to finish, with no easy way to skim — 900 characters about a photo of a conference booth is a punishment, not a service.

Spend the room when the image carries information, not when it carries atmosphere. Compare:

The strong version runs about 125 characters and says the thing the image was posted to say. If it had taken 400 characters to get there, 400 would have been right. Length should follow the content, not the size of the box.

The one thing X won't let you undo

Alt text on X is set at compose time and stays that way. There's no way to add or edit a description on a post that's already live. If you skipped it or got it wrong, the only real fix is deleting the post and publishing it again — which means giving up whatever replies, reposts, and likes it had collected.

That's a meaningful difference from a CMS, where alt text is a field you can revisit for years. On X, the thirty seconds before you press post are the only thirty seconds you get. It also means the "let's audit our old posts" project doesn't really exist here; go back far enough and there's nothing left to repair, only a habit worth changing going forward.

The habit that makes it stick

Write the description while the image is still in front of you and the reason you chose it is still in your head. Coming back to it later — from a scheduler, from a spreadsheet, from a folder of filenames — is where the effort balloons and the field quietly gets skipped.

One thousand characters is the most generous alt text field on any major platform except Bluesky. Treating it as an optional extra is the expensive habit. Treating it as a sentence or two you write before every post is not.