How to Write Alt Text for Social Images: Rules and Examples
Quick answer: write alt text in one or two sentences that describe what the image shows and any text it carries, start with the subject rather than "photo of", and keep it within the platform's field limit. X allows 1,000 characters, Bluesky 2,000, TikTok around 300; the accessibility rule of thumb is under 125 characters regardless.
Why alt text matters
Screen readers read alt text aloud, and the platforms that index it also surface it in search. Mastodon's full-text search indexes descriptions, and X's image search reads them. A launch graphic with no alt text is invisible to a slice of the audience and loses a discovery channel at the same time.
Auto-generated alt text is not a substitute. It usually identifies the category ("a person standing outdoors") and misses the product, the headline, and the point of the post. Override it every time.
The field limits
| Platform | Alt text field | Practical target |
|---|---|---|
| X | 1,000 characters | 100–200 |
| Bluesky | 2,000 characters | 100–200 |
| TikTok | ~300 characters | 100–150 |
| 120–1,000 (client varies) | Under 120 | |
| 100–1,000 (client varies) | Under 125 | |
| Recommended under 150 | 100–150 |
The limits conflict across clients because the editors change, so write to the smaller number and you never get cut.
How to write it
- Start with the subject: "Dashboard showing a weekly revenue chart" beats "Image of a screen".
- Include text in the image verbatim. If the graphic says "Ship in under a minute", the alt text should carry it.
- Skip filler. "Photo of", "image of", and descriptions of color for color's sake add nothing.
- Describe function when the image is a link: "Button linking to the signup page".
- Leave decorative images empty (
alt="") so screen readers skip them.
Text-heavy graphics
Launch graphics and quote cards are mostly text, and the rule is to reproduce that text. It is the one case where longer alt text is correct, because the image's content is the copy.
Multi-image posts
Describe each attachment separately; "first of four" is not needed because the reader hears the order. Keep the descriptions consistent in length.
The launch workflow
A finished launch set includes the images, the captions, and the alt text together, and Neatico drafts the descriptions alongside the graphics from a single product brief so the accessibility layer is not an afterthought.
Frequently asked questions
How long should alt text be? One or two sentences, roughly 100–200 characters; the accessibility convention is under 125. Text-heavy graphics can run longer.
Does Instagram auto-generate alt text? Yes, but it is generic. Override it from Advanced settings before you publish.
Should I include "photo of"? No. Start with the subject; the listener already knows it is an image.
What if the image contains text? Reproduce that text in the description. The color contrast guide covers a separate accessibility issue.
Related guide: the GEO guide.