How to add alt text on social media

Every major social platform has a field for alt text, but each one puts it somewhere different, and a few hide it behind a menu you would never open by accident. This guide gives the current steps for Bluesky, Mastodon, X, LinkedIn, Instagram and Facebook. Each set of steps was checked against the platform's own help pages or source code in October 2026, and each section links to that source so you can check for changes.

If you are new to writing the description itself, start with what makes alt text useful, then come back here to find the field.

Before you start

Three things are the same everywhere:

• Alt text belongs to the image, not the post. If you attach four images, each one has its own field.
• Add it before you post. Some platforms let you change it afterwards, some do not. The sections below say which.
• The post text does not replace it. A screen reader reads your post and then, separately, the alt text for each image. Write the alt text to describe the image, and let the post carry your comment on it.

How much you can write differs a lot between platforms. We keep a separate, dated list of alt text character limits.

Bluesky

On Bluesky, the alt text button sits on the image itself in the post composer. The steps below come from the Bluesky app's open source code, which is the same on the web, iOS and Android.

1. Start a new post and add an image.
2. Select ALT on the image thumbnail. Screen readers announce it as "Add alt text".
3. Write the description in the Alt text field.
4. Select Save. Repeat for each image, then post.

Bluesky has no way to add alt text to a post that is already published. Adding it retroactively is an open feature request, so get it right before you post.

Two settings help. Under Settings, then Accessibility, turn on Require alt text before posting, and Bluesky will not let you post an image without a description. Display larger alt text badges makes the ALT badge on other people's images easier to spot.

Mastodon

These steps are for Mastodon's web interface, as described in the Mastodon documentation on posting. Mastodon apps and other fediverse software put the option in a similar place, on the attached image, but the labels vary.

1. Attach an image to a new post.
2. Select Edit on the attachment thumbnail. Thumbnails without a description show an ALT badge with a warning icon.
3. Write the description in the field marked "Describe this for people with visual impairments". If the image contains text, Add text from image copies that text into the field for you to check.
4. Select Done, then post.

Since Mastodon 4.4, the web interface reminds you to add alt text when you try to post media without it. The reminder can be turned off in your preferences, but it is worth leaving on.

Mastodon lets you edit a published post, and the edit includes media descriptions (the media_attributes field in the statuses API). So if you notice a missing description later, edit the post rather than deleting it.

X (Twitter)

X calls alt text an "image description". The steps are from X's help article How to add image descriptions and are the same on iOS, Android and the web.

1. Add an image to a post.
2. Select +ALT on the image.
3. Type the description. The character count is shown in the corner of the box.
4. Select Done. The badge changes to ALT without the plus sign. Then post.

X's help only covers adding and editing descriptions before you post, so treat the description as final once the post is live. X also documents step-by-step instructions for VoiceOver, JAWS and NVDA if you post with a screen reader yourself. Descriptions cannot be added to videos.

LinkedIn

LinkedIn's help article Add alternative text to images for accessibility covers both desktop and mobile.

• Desktop: after uploading an image, select Alt. text below the image, write the description, and select Save.
• Mobile: after uploading an image, tap ALT below the image, write the description, and tap Done.

LinkedIn may add alt text automatically to images that do not have it. On desktop you are told when that happens, on mobile you are not, so it is worth opening the field and replacing the automatic text with your own.

Instagram

Instagram hides alt text in a menu on the last screen before you share. The steps are from Instagram's help article Edit the alternative text for a post on Instagram.

In the iPhone or Android app, before you share:

1. Take or upload a photo and tap Next.
2. Choose a filter or edit, then tap Next again.
3. Tap More options.
4. Tap Write alt text, write the description, and tap Done.

After you have shared it: go to the photo, tap the options menu, tap Edit, then Edit alt text in the bottom right. Write the description and tap Done.

On a computer: after choosing a filter and editing, click Next, then Accessibility, and write the alt text in the box before you click Share. For an existing post, use the options menu, Edit, then Accessibility.

If you skip this, Instagram uses automatic alt text, which its help page describes as object recognition. It can name what it detects, but it cannot know why you posted the image, so your own description is the better one.

Facebook

Facebook only lets you write alt text before posting on a computer. In the apps, you add it once the post is up. The steps are from Facebook's help article Edit the alternative text for a photo on Facebook.

On a computer, before you post:

1. Click Photo/Video at the top of your Feed and choose the photo.
2. Hover over the photo and click Edit.
3. Click Alternative text in the menu on the left.
4. Click Custom alt text, write the description, and click Save.

On a computer, after posting: open the photo, click the options menu in the top right, choose Change Alt Text, write the description, and click Save.

In the iPhone or Android app, after posting: go to the post and tap the photo, tap the options menu in the top right, then Edit alt text. On iPhone, tap Override generated alt text first. Write the description and tap Save.

Like Instagram, Facebook fills in automatic alt text that starts with "Image may contain:" when you do not write your own.

What to write once you find the field

The field is the easy part. A few rules cover most images:

• Start with the subject. Skip "Image of"; the screen reader already says it is an image.
• Say what matters for this post. The same photo needs different alt text in a post about the venue and a post about the speaker.
• Quote text that carries meaning. Signs, headlines and anything you would expect a reader to read.
• Keep it to what the image shows. Your opinion of it belongs in the post.

Here is the difference on a typical post, a photo shared with the text "Finally finished the garden path":

• Weak: "Garden."
• Better: "A new path of grey stepping stones curving through a lawn to a wooden shed, with low lavender planted along both edges."

For specific kinds of images there are separate guides: alt text for screenshots, alt text for charts and graphs, and how long alt text should be.

A faster way on these sites

If you post a lot of images, the AltKit browser extension adds a Create Alt Text button to the alt text dialog on Bluesky, X, Mastodon (on mastodon.social, mastodon.online and mstdn.social), LinkedIn, Instagram and Facebook. It writes a description into the field, which you read and correct before posting. You can also upload a single image in the web creator. Both are free with an AltKit account, as explained in free use and the daily limit.

Whichever way you write it, the steps above are where it goes. The platforms change their interfaces from time to time, so if a button has moved, the linked help page for that platform is the place to check.