Describe the picture as you would to someone on the phone: what it shows, and any text in it.
Alt text is also how people who cannot see the image take part in the post.
Glossary
Alt text: what it means
Alt text is a short written description of an image, read aloud by screen readers and shown when the image does not load. Good alt text states what matters in the picture in a sentence. Instagram, Bluesky, Mastodon and X let you add it per image, and 1Post gives each image a field.
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Free tools
Count characters the way each network does, split threads and preview posts. No account needed.
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API and MCP
Post to every network from your own code or assistant with one key, signed webhooks and idempotent requests.
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How long should alt text be?
One or two sentences. Networks set their own limits, and Mastodon, for example, publishes 1,500 characters on the instance we read.
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