Alt text
Alt text (alternative text) is a short written description attached to an image, GIF, or other visual, which screen readers read aloud for people who are blind or have low vision, and which appears in place of the image if it fails to load.
Quick facts
- Also known as: alternative text, image description, alt tag, alt attribute
- Category: Accessibility & content
- Applies to: X · Instagram · Facebook · LinkedIn · Bluesky · Threads · Pinterest · websites
- Character limits: X up to 1,000 characters, Bluesky up to 2,000 characters per image
- Key trait: it makes visual content understandable without seeing it
What is alt text?
Alt text started on the web. The HTML "alt" attribute lets a developer add a text description to an image so browsers and assistive technology can describe it. Social platforms adopted the same idea as images became the center of most feeds, first with automatically generated descriptions, and later with fields where users write their own.
Good alt text describes what matters in the image in the context of the post. "Photo" is not useful. "A barista pouring latte art in the shape of a heart into a white cup" is. If the image contains text, like a quote card or infographic, the alt text should include that text, because a screen reader can't read words that are part of an image.
Alt text on different platforms
X (Twitter): add a description to each image or GIF before posting, up to 1,000 characters. Posts with alt text show an "ALT" badge. See how to add alt text on Twitter.
Bluesky: allows up to 2,000 characters of alt text per image.
Instagram: generates automatic alt text, and you can write your own under Advanced settings when posting or by editing an existing post.
Facebook: creates automatic alt text with object recognition, which you can override with a custom description.
LinkedIn: lets you add alt text to images when creating a post.
Why alt text matters
Alt text is first an accessibility practice: millions of people use screen readers, and without descriptions, image-based posts are empty to them. It also helps when images load slowly or fail, and it gives platforms and search engines more context about your content, which can support discoverability in image and platform search. Writing alt text is a small habit that makes a brand's content usable for more people. This roundup of how to add alt text to images on social media compares tools that make it easier.
How Circleboom helps with alt text
With the Circleboom Publish tool, you can add alt text to images while you create a post. After uploading images or choosing them from Unsplash or Canva, open the preview section and click the book icon to write the description. Circleboom Publish supports alt text for X, Facebook, Pinterest, LinkedIn, and Google Business Profile, so you can prepare images, GIFs, and their descriptions for several accounts in one place before scheduling. The steps are covered in the Circleboom help guide on adding alt text to images. For image-heavy formats, also see how to create carousel posts on Instagram.
Frequently asked questions
How long should alt text be? Usually one or two clear sentences is enough. Use more when the image contains important text, like a chart or quote card.
Should alt text include hashtags or keywords? No. Write for the person using a screen reader. Keyword stuffing makes the description harder to understand.
Should I start alt text with "image of"? No. Screen readers already announce that it's an image, so start with the description itself.
Related terms: What is a GIF? · What is a carousel post? · What is a header image? · What is a cover photo?
By Arif Akdoğan, reviewed by Kevin O. Frank. Last updated 2026-09-27.
Sources: Social media character limits references (2026) for X and Bluesky alt text; Circleboom Help, "Adding alt-text to images."
