How to add alt text on Mastodon

Mastodon supports alt text up to roughly 1,500 characters (some instances vary). Add descriptions while composing.

Steps

1. Create a post and attach an image or GIF.
2. Choose Add description under the image.
3. Write a clear description and include any important on‑image text.
4. Save, then publish.

Alt text is viewable via the ALT badge on media attachments.