Alt text is written image description that helps screen readers and search systems understand visual content.
On social media, alt text makes images more accessible to people using assistive technology.
Good alt text explains the important visual information in a clear, useful way without stuffing keywords.
Alt text should describe what matters in the image for understanding the post, including text shown in the image when that text is important.
Describe what matters in the image for understanding the post, in a sentence or two, including any important text shown in the image. Skip filler like "image of" and do not stuff keywords.
Instagram, Facebook, X, LinkedIn, Pinterest, Threads, Bluesky, and Mastodon all support alt text on images, either during posting or as an edit afterwards.
Its main job is accessibility for screen reader users. It also helps platforms and search engines understand image content, which can support discovery, but write it for people first.