Alt text for GIFs and short video thumbnails

You post a six-second product GIF, or a Reel with a bold cover frame, and reach for the alt text field out of habit — the same one you fill in for every photo. On most platforms, it isn't there. That field marketers have trained themselves to look for quietly disappears the moment the upload is a GIF or a video, and that gap trips up more accessible teams than any actual writing question does.

Here's what's actually possible, platform by platform, and what to do everywhere the field simply doesn't exist.

The one place GIF alt text really works

X (formerly Twitter) supports alt text on GIFs the same way it does on photos — up to 1,000 characters, added through the same +ALT button before you post. Bluesky and Tumblr support it too. That's a short list. Most of the platforms marketers post to daily aren't on it.

One catch worth flagging on X: once the post is live, the alt text is locked. There's no editing it in afterward, so it has to be right the first time, same as the post itself.

Where the field just isn't there

Instagram, Facebook, and LinkedIn all let you write alt text for a static photo post. None of them give animated GIFs or video posts an equivalent field. If someone using a screen reader opens a video post on these platforms, what they get is your caption — nothing describing the cover frame or the motion itself, unless you've put it there yourself.

Writing the description into the caption

The fix is unglamorous: fold a short visual description into your caption, the same way you'd write alt text, right where a sighted viewer sees it as your opening line. Lead with what's happening on screen, not what the file is called.

The same logic applies to a video's cover thumbnail. Don't caption it as "video thumbnail" and don't leave it to whatever frame got auto-selected — describe what's actually on screen in the first sentence of your post. For anyone using assistive tech, that sentence is often the only information they get before deciding whether to keep watching.

What this means for a content calendar

Treat GIFs and short video posts as their own checklist item, not a variant of the photo one. A workflow that ends at "did I fill in alt text" will silently skip every GIF and video post, because the field it trained you to look for won't be sitting there waiting. Build the habit at the caption-writing stage instead, while the context is still in your head.

None of this changes what you do for photos — that part still takes a couple of seconds. Folding a description into a GIF or video caption is still a manual step for now. But knowing which platforms even offer the option, and which ones fold it into the caption whether you like it or not, is most of the battle.