Alt text is a short written description attached to an image so that people using screen readers, or anyone whose images fail to load, can understand what it shows.
What good alt text looks like
Alt text describes the content and purpose of an image in plain language. Screen readers read it aloud. X, LinkedIn, Bluesky, and Mastodon all let you add it to images in posts.
Guidelines:
- Describe what matters for the post, not every detail.
- Include any text shown in the image, such as a headline in a screenshot.
- Skip "image of" or "picture of"; the screen reader already says it is an image.
- Keep it to one or two sentences for most images.
An example
Weak: "screenshot." Better: "Release notes for version 2.4 listing three changes: faster sync, dark mode, and a new CSV export."
Why it matters for AI-agent publishing
Agents often attach images, charts, or screenshots and skip the description. On Mastodon in particular, posts without alt text are widely seen as poor etiquette, and on every network they exclude blind and low-vision readers.
SocialHandoff publishes images with alt text on all four core networks and includes a guardrail that flags a missing description before the post can go out. An agent can draft the alt text along with the post, and the reviewer checks both in the approval inbox. See image dimensions per network in social media image sizes.