Social media alt text: a practical checklist with examples

Good alt text gives someone the information an image adds to a post. It isn’t a second promotional caption or a place to repeat search keywords. Think about what the reader is trying to do, then describe what they need to understand without seeing the image.

This guide uses three made-up examples: a repair photo, an event poster and a small chart. The method works in any tool that supports image descriptions, but always check the saved draft and the published post on each network.

Decide what the image adds

Read the post without its image. What’s missing? Maybe it’s the position of a broken part, the event details, a comparison or a deliberate visual style. Write that down before you list colors and objects. The W3C image decision tree helps you work out an image’s purpose.

Social networks don’t offer the same image options as a website’s HTML. Leaving the description empty doesn’t reliably mark an image as decorative. If an image adds nothing useful, ask whether the post needs it at all.

Describe a photo with relevant detail

For a repair tip, “Photo of a chair” misses the point. A more useful draft is: “Underside of a wooden chair: the rear-left corner bracket is loose, with a visible gap between the bracket and seat.” The post itself can explain the repair.

Include where things are, any readable labels and details that support the lesson. Don’t guess at a cause you can’t see, or at a person’s identity or feelings. Make sure the description matches the final crop; a reused description can mention something that’s no longer in the picture.

Make poster text available as text

For an event poster, include the details people need to act: “Community repair workshop, 16 October 2026, 18:00–20:00, Riverside Library, free registration required.” This is only an example, not a real event. The post should also include a working registration link and the time zone when it matters.

Don’t put important instructions only inside an image. If the same details are already in the post text, keep the image description to what the image adds. Leave out unrelated hashtags, sales language and long tracking links.

Explain charts beyond their appearance

For a simple example, “Bar chart: workshop registrations rose from 12 in week one to 18 in week two” gives the values and the comparison. These numbers are made up. Include the units and the time period, so readers get more than “the blue bar is taller.”

A complex chart may need a short description plus a table or longer explanation linked from the post. W3C’s complex-image guidance explains that approach. Don’t cut important data to hit a word count, and don’t claim a chart proves more than it shows.

Keep the description attached through edits

Keep each final image next to its description in your planning notes. When you replace, crop or reorder images, check that each one still has the right description. Translate descriptions for your readers, including any important text inside the image. Keep numbers, names and the order of images in a series.

Use the publishing tool’s image description field where it has one, then reopen the saved draft. Not every tool passes the description on to every network. If a network can’t keep the information, put it in the post text or on a linked page instead.

Check what readers actually get

After publishing, open each image and its description in the network’s own app. Use a screen reader or other accessibility tools if you can, and check that the description still makes sense next to the post. A successful upload doesn’t prove the description arrived.

Alt text for a still image doesn’t replace captions for speech or important sound in a video; W3C’s captions guidance covers that separately. Keep the cross-posting checklist nearby. In Studio, you add a description to each image as you write the post, and it goes out with the image to networks that support descriptions, such as X (Twitter), Bluesky and Mastodon. Studio isn’t available yet; you can join the waitlist.