How to write alt text for social media posts, platform by platform

Alt text (alternative text) is a written description attached to an image. Screen readers read it aloud, so people who are blind or have low vision know what the image shows. Each of the seven social media platforms covered below has a field for it, usually a tap or two away from the caption.

A useful description says what the image adds to the post, leads with the most important detail and stays short. The advice below draws on the images tutorial from the World Wide Web Consortium’s Web Accessibility Initiative (opens in a new tab) (W3C WAI) and on each platform’s own help pages as of November 2026.

Work out what the image is for

The W3C tutorial says the right text alternative depends on the image’s purpose and context, and that the author has to make that call. Its example is a photo of a bird: the species may hardly matter on a site about parks, yet matter a great deal on a site about birds.

Most images in social posts fit one of four types:

• Photos and illustrations. Give a short description of the essential information. W3C’s page on informative images (opens in a new tab) notes that this is usually not a literal account of everything in the frame.
• Images of text. Quote cards, flyers and screenshots need alt text with the same words that appear in the image.
• Charts and infographics. W3C’s guidance on complex images (opens in a new tab) calls for a short description that identifies the image, plus a longer text version of the information that everyone can reach. Our read: on social, put the longer version in the post text, a reply or a linked page.
• Carousels. For a set of related images, W3C’s page on groups of images (opens in a new tab) says each one needs its own description.

Write the description

W3C’s tips on text alternatives (opens in a new tab) carry over well to social posts:

1. Lead with what matters. Put the most important information first.
2. Keep it brief. Aim for the most concise description of the image’s purpose, usually a phrase or a sentence. If you need more, move the detail into the post itself.
3. Skip “image of” and “photo of”. Screen readers already announce an image. Name the medium only when it matters, such as a painting or an illustration.
4. Punctuate normally. Punctuation makes a description easier to understand.
5. Use the language of the post. W3C’s explanation of the Web Content Accessibility Guidelines (WCAG) rule on non-text content (opens in a new tab) says text alternatives should match the language of the content.

For example, on a post announcing a store opening, “Shop front with a green awning and a line of people along the sidewalk” tells a reader far more than “Store”.

Leave hashtags, links and sales copy out. Our read: the field is there to describe the image, and the Instagram, Facebook, Threads and Pinterest help pages all say the text is only read out to people using a screen reader.

Find the alt text field on each platform

Platform	Where to add it	Stated limit
X	Select +ALT on the uploaded image, write the description, then select Done	1,000 characters
Instagram	App: after the edit step, More options, then Write alt text. Computer: Accessibility	None stated
Facebook	Computer: hover over the photo and select Edit, then Alternative text and Custom alt text	None stated
Threads	More on the attached photo or video, then Add alt text (Alt on Android)	None stated
LinkedIn	Alt.text below the uploaded image on desktop, ALT on mobile	None stated
Pinterest	Web: More options in the Pin form, then Alt text. Standard and video Pins only	500 characters
TikTok	Photo posts in the app: More options on the post screen, then Add alternative text	300 characters per photo

These steps and limits come from the help pages for image descriptions on X (opens in a new tab), alt text on Instagram (opens in a new tab), alt text on Facebook (opens in a new tab), alt text on Threads (opens in a new tab), alternative text on LinkedIn (opens in a new tab), alternative text on Pinterest Pins (opens in a new tab) and accessibility features on TikTok (opens in a new tab), as of November 2026. “None stated” means the page gives no figure. Menus change, so check the linked page if a label does not match.

Two more details from those pages:

• Editing later. Instagram, Facebook, Pinterest and TikTok document how to change alt text after publishing. The X, Threads and LinkedIn pages only describe adding it while you compose, so add it before you post.
• Visibility on X. An ALT badge marks images that have a description, and anyone can select it to read the text.

As of November 2026, none of these help pages says alt text changes a post’s reach or ranking. Treat it as an accessibility task, not a growth tactic. If your organization has to meet a legal accessibility standard, ask a qualified professional how it applies to your social content.

Frequently asked questions

Should alt text repeat the caption?

No. Use it for what the image shows that the caption does not say. W3C’s guidance on informative images takes the same approach: the description covers what is shown visually but not explained in the nearby text.

Is automatic alt text good enough?

Instagram, Facebook and Threads generate alt text automatically, and LinkedIn may add its own. The three Meta help pages say you can replace it with a better description. Our read: automatic text cannot know why you chose the image, so write your own for anything that matters.