Alt text for social media is a short written description of an image. Screen readers read it aloud to people who can't see the picture, and it shows up when an image fails to load. Every network covered here has a field for it. Most of them hide that field one tap away from the post button.
Once you know the pattern, it takes about twenty seconds per image. Below: where the field lives on Instagram, Facebook, X, LinkedIn, Bluesky, Mastodon and Threads (checked October 2026), a formula that works for almost any image, and examples of weak and strong alt text.
The short version
Describe what matters in the image, in the order someone would notice it, in one or two sentences.
Don't start with "image of". The screen reader already says it's an image.
If the image contains words, those words belong in the alt text.
All seven networks in this guide have an alt-text field. You just have to open it.
What alt text is, and who relies on it
Alt text (alternative text) never appears in the feed. Screen readers like VoiceOver and TalkBack read it out, and X's help centre notes it also helps people on slow connections.
The audience is bigger than most marketers assume. The World Health Organization estimates that at least 2.2 billion people have a near or distance vision impairment. Not all of them use a screen reader, but for the people who do, a post with an image and no description is a post with a hole in the middle.
Platforms try to fill that hole with automatic alt text. Instagram, Facebook, Threads and LinkedIn all generate a description with object recognition when you don't write one. It's better than nothing, but it tends to produce something like "may be an image of 2 people and food". That tells a listener nothing about your new momo platter or the discount printed on your poster.
Some people add alt text hoping it helps reach. The platforms don't say whether it does, and writing for an algorithm is how you end up with keyword soup. Write it for the person listening.
Where to add alt text on each platform
Here's where to find the field. "Not published" means the platform's help pages don't state a limit, not that there isn't one.
Platform
Where the field is
Character limit
Accessibility, on the screen before you share
Not published
Edit on the photo, then Alternative text
Not published
X
The +ALT button on the image
1,000
Alt. text (desktop) or ALT (app) under the image
Not published
Bluesky
The +ALT button on the image
2,000 in the official app
Mastodon
Edit or ALT on the attachment
10,000 on Mastodon 4.6+, 1,500 on older servers
Threads
More on the attachment, then Add alt text
Not published
After you choose a photo and edit it, tap Next, open Accessibility and write your alt text, then share. Instagram moves this between app versions, so if it's missing, check More options or Advanced settings. To fix it later, open the post, tap the three dots, choose Edit and open Accessibility again. Instagram's help page covers both routes. In a carousel, write a description for each image, not just the first.
Before posting, hover over the photo, click Edit, then Alternative text. Facebook shows its automatic description first. Click Custom alt text and write your own. For a photo that's already live, open it, click Options and choose Change Alt Text.
X
After uploading, tap +ALT on the image and write up to 1,000 characters. Once it's posted, an ALT badge appears on the image, and anyone can tap it to read the description. So sighted people read your alt text too. Each image in a multi-image post has its own badge.
On desktop, click Alt. text below the image after uploading. In the app, tap ALT. LinkedIn's help page says it may add automatic alt text to images that don't have any, and won't tell you when it does on mobile.
Bluesky
Tap +ALT on the image. The official app allows up to 2,000 characters. It also has a setting worth switching on for team accounts: Settings, Accessibility, "Require alt text before posting".
Mastodon
Click Edit (or ALT) on the attachment and write the description. Mastodon 4.6 raised the limit to 10,000 characters, and mastodon.social reports that limit today, but servers on older versions still cap it at 1,500. Alt text is a strong community norm there, and images without it get noticed.
Threads
On threads.com, attach the photo or video, click More at the bottom left of it and choose Add alt text. In the app, tap Alt on the attached photo. Threads supports alt text on videos as well as photos. Its help page only covers adding alt text before you post, so get it right first time.
A simple alt text formula
Most good alt text follows the same shape:
What it is + the detail that matters here + any text in the image.
The middle part is where people go wrong. Ask yourself why you posted this particular picture. Whatever the answer is, it belongs in the alt text. If you're a Pokhara hotel posting a room photo to show off the lake view, the lake view is the point, not the bedspread.
A few working rules:
Lead with the subject. "Barista pouring latte art" before "wooden counter, morning light".
Keep it to one or two sentences for most photos. Around 100 to 200 characters covers it. Infographics and text-heavy images need more.
Use plain words. Write the way you'd describe the photo to a friend on the phone.
Name people if your caption would. "Our head chef Sita" is more useful than "a woman in a chef's hat".
Good vs bad alt text for social media: examples
Here's the formula applied to five common kinds of social image.
Image
Weak alt text
Better alt text
Team photo
Image of people
Our five baristas in green aprons, laughing behind the counter on opening morning at our Thamel café.
Product shot
Leather bag, best handmade bag Nepal, gift idea, sale
Tan leather tote with a brass zip and two short handles, on a white table next to a laptop for scale.
Quote card or poster
Tihar sale poster
Mustard poster with the text: Tihar sale, 20% off all lamps, 1 to 5 November. Shop logo bottom right.
Infographic
Chart about posting times
Bar chart of our Instagram reach by weekday. Tuesday and Thursday are highest, about 4,000 each. Sunday is lowest, about 1,200.
Meme
Funny meme
Distracted-boyfriend meme. The boyfriend, labelled "me", turns to stare at "a new scheduling tool" while his girlfriend, labelled "my 47 unposted drafts", glares at him.
For memes, naming the format helps people who know it, and describing the labels helps the people who don't. Describe the joke, not just the pixels.
What not to do
Starting with "image of" or "picture of". The screen reader has already said it's an image. The exception is when the medium matters: "Screenshot of a customer review" or "Watercolour of Phewa Lake" is fine.
Keyword stuffing. "Best momo Kathmandu momo delivery cheap momo" helps nobody and sounds like spam when read aloud.
Pasting the caption. If the caption already says "New menu is live", the alt text should describe what the menu looks like, not repeat the announcement.
Putting hashtags, credits or links in it. Hashtags read aloud are painful, and links in alt text aren't clickable.
Leaving the automatic text in place. Read what the platform guessed. It's often wrong, and almost never says why the image matters.
Alt text for text-heavy graphics
Quote cards, event posters, tip carousels and infographics are where alt text matters most. To a screen reader, words baked into a JPEG are just pixels.
The rule is simple: transcribe the text. For a quote card, give the quote and who said it. For an event poster, include the event name, date, time and place in a sensible order, then mention the visual style briefly if it matters to your brand.
Carousels need one description per slide, each with that slide's words. For a 10-slide tips post, put the full text in the caption too.
Charts are different. Don't read out every data point. Give the takeaway and the key numbers, like the infographic row above, and put the full data in the caption or a link.
Long menus are the one place we'd bend the rule. Describe the image ("Our winter menu, printed on brown paper") and put the items in the caption or on your website.
Making alt text a habit
The hard part isn't writing alt text. It's remembering. Write it when you write the caption, before you schedule. If you work with a team or a client, add "alt text on every image" to your pre-publish check.
In GoBrandIt, each image you attach to a post has an alt-text dialog, and "Write with AI" drafts a description for you. Treat it as a first draft. AI is good at saying what's in a picture and much worse at knowing why you posted it, so add names, the detail that matters and any text in the image before you save. It's part of our AI content assistant, which also writes and rewrites captions. If you're still building the posting routine itself, our guide on how to schedule Instagram posts walks through it.
Hashtags go in the caption; our Instagram hashtag strategy guide covers how many to use. For the caption itself, see writing social media captions with AI.
Alt text in seconds, not minutes
"Write with AI" drafts alt text for every image you schedule in GoBrandIt. Free forever for 3 accounts.
Questions people ask
How long should alt text be on social media?
One or two sentences for most photos, roughly 100 to 200 characters. Text-heavy graphics need more. X allows 1,000 characters and the Bluesky app 2,000.
Can I add alt text after a post is published?
On Instagram and Facebook, yes: edit the post (Instagram) or open the photo and choose Change Alt Text (Facebook). Threads' help pages only describe adding it before you post, so don't count on fixing it later there.
Does Instagram add alt text automatically?
Yes, as do Facebook, Threads and LinkedIn. It's generic and usually misses the point of the image, so write your own.
Should I put hashtags or keywords in alt text?
No. Alt text is read aloud to people using screen readers, and hashtags or keyword lists make it hard to follow. Keep hashtags in the caption.
Do videos need alt text?
Threads lets you add alt text to videos. On other networks, the main accessibility tool for video is captions, so turn them on and make sure anything important on screen is also said out loud or written in the caption.
Platform details checked October 2026 on the official help pages of X, Instagram, Facebook, LinkedIn and Threads, Bluesky's and Mastodon's published app code, and the WHO fact sheet on vision impairment. Platforms change these settings from time to time. If you spot something out of date, let us know.