Alt Text Character Limits for Every Social Network

X allows 1,000 characters of alt text per image and Pinterest 500 per Pin, each according to the network’s own help pages, and TikTok allowed 300 per description on photo posts as of February 2026. Instagram and Threads publish no figure in their help centres, but their publishing APIs accept up to 1,000 characters; LinkedIn’s API documentation allows 4,086, and Bluesky’s own app stops at 2,000 while its protocol sets no maximum. Facebook publishes no limit anywhere we could find, and no alt text field is documented for YouTube or Google Business Profile on the pages read.

These figures were read on October 12, 2026, except TikTok’s, which comes from a copy of its support page archived on February 4, 2026, because TikTok’s support site could not be reached on the day. This post covers the ten networks Postnavo is launching with. Each figure links to the page it was read from, with the sentence quoted, and “not documented” means the network’s pages are silent, not that there is no limit.

Alt text limits at a glance#

Two figures appear for LinkedIn in the pages read for this post, 300 and 4,086. The LinkedIn section says where each comes from.

X (Twitter) alt text character limit#

X allows 1,000 characters per image description. The how-to page in X’s help centre shows the counter: “We’ve used 178 characters of the 1,000 characters available.” Two more help pages give the same figure (accessible images, writing descriptions), and the X API’s media metadata schema gives the alt text a maximum length of 1000.

To add a description, upload an image to a post, then select the +ALT button on the image in the iOS and Android apps, or “Add description” underneath the image on the web. Each image in a post takes its own description.

X’s help page says “Image descriptions cannot be added to videos.” GIFs are not documented on the help pages read. Changing a description after posting is not documented either: the page describes editing it only “prior to posting”.

Related page: scheduling X posts.

LinkedIn alt text limit#

LinkedIn’s help page on alt text gives no character limit. The figure comes from LinkedIn’s API documentation, which says of the alt text field: “Maximum length is 4,086 characters, recommended length is less than 120 characters.” The same sentence is on the Images API page and the MultiImage API page. So 4,086 is the documented ceiling for tools that post through LinkedIn’s API. What LinkedIn’s own composer accepts is not documented.

The 300 figure is on no LinkedIn page read for this post. It is on Buffer’s help page, checked October 12, 2026, which lists “LinkedIn - 300 characters” among the alt text limits of Buffer’s own composer. That is a limit of that tool, not a figure from LinkedIn.

To add alt text, upload an image, then click “Alt.text” below it on desktop, or tap “ALT” below it on mobile. The help page also says LinkedIn “may automatically add alt-text to images that don’t have it”: on desktop you are alerted when that happens, on mobile you are not. Changing alt text after posting is not documented.

Related page: scheduling LinkedIn posts.

Instagram alt text character limit#

Instagram’s Help Center article gives steps and no character limit. The figure is in Instagram’s publishing API documentation: “Alternative text, up to 1000 character, for an image.” The same entry says: “Only supported on a single image or image media in a carousel.” and “Reels and stories are not supported.” The API field dates from March 24, 2025. Whether the app’s own field stops at 1,000 is not documented.

In the iPhone app, pick a photo and tap Next past the filter screen, then tap More options, then Write alt text, write it and tap Done. On a computer, after the filter step, click Accessibility and write the alt text in the box before you share. To change it after posting in the iPhone app, go to the photo and tap Options, tap Edit, then Edit Alt Text in the bottom right.

If you write none, Instagram’s automatic alt text describes the photo with object recognition, and you can replace it. The Help Center says the description is read only to someone using a screen reader.

Facebook alt text limit#

Facebook publishes no alt text limit. The Help Center article has steps only, and the Graph API reference describes the field, alt_text_custom, as “Accessible alternative description for an image” with no length.

On a computer, click Photo/Video at the top of your Feed and select the photo. Hover over the photo and click Edit, click Alternative text in the menu on the left, then click Custom alt text. For a photo you have already posted, click the photo to open it, then click Options in the top right and select Change alt text.

Related page: scheduling Facebook Page posts.

Threads alt text limit#

The Threads help article gives no figure. The Threads API reference does: “The maximum length of alt_text is 1,000 characters.” On Threads, alt text covers photos and videos.

On threads.com, click More at the bottom left of an attached photo or video, click Add alt text, enter it and click Done in the bottom right. In the Threads app for Android and iPhone, tap More at the bottom of an attached photo or video, tap Add alt text, enter it and tap Done in the top right.

Changing alt text after posting is not documented. Threads’ page on editing a post says “Only the text of a post can be edited” and does not mention alt text.

Bluesky alt text limit#

Bluesky has two answers, one for the protocol and one for its own app.

• The protocol sets no maximum. The lexicon for image embeds defines alt as a string, “Alt text description of the image, for accessibility.”, with no maximum length. The video embed’s alt is defined the same way.
• Bluesky’s own app stops at 2,000 characters. Its public source code sets MAX_ALT_TEXT = 2000, with a comment that 100 is the recommendation, “but increasing limit per user feedback”. Past the limit, the app’s alt text dialog says “Alt text will be truncated.”

The 2,000 figure comes from the app’s source code: no Bluesky help page stating a figure was found. As far as the lexicon goes, other Bluesky clients and tools are not bound by that number. In Bluesky’s app, alt text goes in the “Add alt text” dialog on an attached image in the composer. Changing it after posting is not documented.

Related page: scheduling Bluesky posts.

TikTok alt text limit#

TikTok has alt text on photo posts. TikTok’s European newsroom said on May 23, 2025: “We recently introduced alternative text for photo posts, which allows creators to add alt text during upload or after publishing.”

The limit is 300 characters per description, according to TikTok’s support page as archived on February 4, 2026: “You can add up to 300 characters for each description.” That support address now redirects to a new TikTok help page, which could not be loaded on October 12, 2026, so the figure was not compared with the live page. Open that page before you rely on this number.

According to the same archived page, on the post screen you tap More options, then Add alternative text, and enter alt text next to each photo. For a photo you have already posted, open its More options, tap Edit post at the bottom, then Add alternative text.

In the same May 2025 article, TikTok said it was “testing a new feature that leverages artificial intelligence to generate alt text”. Whether that shipped is not documented in the pages read. Whether TikTok’s API carries alt text was not checked.

Pinterest alt text limit#

Pinterest allows 500 characters. Its help page says: “Under Alt text, explain what people can see in the Pin (500 characters max)”. The API matches: alt_text has a maximum length of 500 in the schemas for creating and updating a Pin. The help page limits it to two formats: “At this time, you can only add alternative text to standard Pins or video Pins.”

On the web, scroll down and select the drop-down next to More options. In the app, scroll down and tap Advanced Settings. You can edit alt text after publishing. In one set of the app’s edit steps, Pinterest tells business accounts to “use the web to edit alt text”.

Related page: scheduling Pinterest Pins.

YouTube and Google Business Profile: no alt text field documented#

On the pages read on October 12, 2026, neither network documents an alt text field. YouTube’s Create a post help page covers image posts and says nothing about alt text, and the Videos resource of the YouTube Data API has no alt text property. Google Business Profile’s help pages for photos and posts do not mention it. Its API gives a media item a “description”, which Google does not call alt text. That is “not documented”, not “not possible”.

Can you add alt text when you schedule a post?#

In each network’s own scheduler#

No scheduling help page read for this post mentions alt text. On LinkedIn, Instagram and Pinterest the scheduler is the normal composer with a date added, and the alt text control is documented on that same composer, but none of the pages says in words that a scheduled post keeps its alt text. Open the scheduled post and look for its alt text before it goes out.

For Threads, no scheduling article was found in its help centre, so there was no page to read. No scheduling page was read for Bluesky or TikTok for this post. Which networks have a scheduler of their own, and how far ahead each network’s own scheduler reaches, is a separate post.

In a third-party scheduler#

One scheduler that documents alt text today is Buffer. According to Buffer’s help page, checked October 12, 2026: “Currently, it is possible to add alt text to static images scheduled to X/Twitter, Mastodon, Threads, LinkedIn, Pinterest, Facebook, Instagram, and Bluesky through Buffer.” The same page says it is not possible for GIFs, Google Business Profile posts or TikTok posts. It lists Buffer’s own limits: 500 characters for Pinterest, 300 for LinkedIn, 1,000 for X, Mastodon, Threads, Facebook and Instagram, and 2,000 for Bluesky.

The networks’ API documentation sets a ceiling for alt text sent through the API: 1,000 on X, Instagram and Threads, 4,086 on LinkedIn, 500 on Pinterest. A tool can also set a limit of its own, as Buffer’s 300 for LinkedIn shows.

How long should alt text be?#

The guidance from the W3C and from X is to keep it short and put the important part first.

• The W3C’s Web Accessibility Initiative says: “The alt text should be the most concise description possible of the image’s purpose.” and “Aim to put the most important information at the beginning.”
• The same page says: “Usually, there’s no need to include words like “image”, “icon”, or “picture” in the alt text.”
• X’s writing guide says: “Previously, some assistive technology (such as screen readers) stopped reading at 200-250 characters. While this is no longer the case, it’s still important to be succinct in your description.”
• X also says: “If there’s text in the image, include it in your description.”

LinkedIn’s API documentation recommends “less than 120 characters”, and Bluesky’s source code cites a W3C recommendation of 100 while allowing 2,000. Those are recommendations, not limits.

For the post itself, the character counter for post text, one of Postnavo’s free tools, checks a draft against each network’s post limit. It does not count alt text.

FAQ#

Does alt text count toward the post’s character limit?#

No page read for this post says it does. The documentation treats them as separate fields: X gives the image description its own counter, and the X, Instagram, Threads and Pinterest APIs take alt text as a parameter of its own, apart from the caption or post text. Where a network’s pages are silent, that is as far as the documentation goes.

Can you add or change alt text after you have posted?#

It is documented as possible on Instagram, Facebook, Pinterest and TikTok, and not documented on X, LinkedIn, Threads or Bluesky. The last column of the table has each network’s answer, and each network’s section names the page it was read from.

Can you add alt text to a video or a GIF?#

It depends on the network. X’s help page rules out videos, Threads and Bluesky cover videos, and TikTok’s alt text is for photo posts only. The “What can carry alt text” column of the table has all ten networks.

Is there a 125-character rule for alt text?#

None of the networks’ pages sets 125, and the W3C tutorial names no number. The figures that do appear are recommendations, and the section on how long alt text should be lists them.

What happens if you leave alt text empty?#

Facebook, Instagram and Threads generate automatic alt text. Facebook’s help page adds a caveat: “The automatic alt text may not always be complete”. LinkedIn “may automatically add alt-text to images that don’t have it”. In May 2025 TikTok said it was testing AI-generated alt text; whether that shipped is not documented in the pages read. For X, Bluesky and Pinterest, nothing is documented about automatic alt text.