Slack Post Character Limit: 4,000 Characters
Last updated June 2026
The Slack character limit is 4,000 characters per post — the official current limit as of 2026. Ferryman caps Slack message text at 4,000 characters and uses section blocks of up to 3,000 characters when public image blocks are included.
How Slack's limit compares to other platforms
| Platform | Character limit | Native threading |
|---|---|---|
| Slack | 4,000 | No |
| X | 280 | Yes |
| Bluesky | 300 | Yes |
| Threads | 500 | Yes |
| Mastodon | 500 | Yes |
| 3,000 | No | |
| 63,206 | No | |
| Substack | 10,000 | No |
| Discord | 2,000 | No |
Slack's 4,000-character limit sits in the middle of the major text platforms — more generous than X's standard limit, tighter than LinkedIn's. Most Slack posts cross-post cleanly to platforms with similar limits, and require thread splitting on platforms with shorter ones.
What happens when you go over 4,000 characters
Slack doesn't have native threading the way X or Bluesky do. Posts longer than 4,000 characters can't be split into a thread automatically — they need to fit in a single post. Fortunately, 4,000 is generous enough that most cross-posted content (even longer Threads or Mastodon posts) lands as a single post without truncation.
Slack media and threading limits
- Images per post: 4
- Alt text on images: Supported
- Video: Supported, up to platform max
- Native threading: No — long content must fit in one post
Cross-posting and the Slack character limit
Slack is supported as a destination in Ferryman. Posts from X, Bluesky, Threads, Mastodon, LinkedIn, Facebook can be cross-posted to Slack, and Ferryman keeps them within Slack's 4,000-character message limit.
Frequently asked questions
What is the Slack character limit in 2026?
Slack's character limit is 4,000 characters per post. Ferryman caps Slack message text at 4,000 characters and uses section blocks of up to 3,000 characters when public image blocks are included.
Can I post longer than 4,000 characters on Slack?
No — Slack doesn't support a way to post longer than 4,000 characters as a single post or thread. If you need more length, consider a different platform or format (like an article or document attachment).
How does Slack's character limit compare to X?
Slack's 4,000-character limit is 3,720 characters longer than X's 280. Posts that fit on X always fit on Slack.
How does Slack's character limit compare to Bluesky?
Slack's 4,000-character limit is 3,700 characters longer than Bluesky's 300. Posts that fit on Bluesky always fit on Slack.
How does Ferryman handle the Slack character limit when cross-posting?
Ferryman watches your origin platform for new posts and replicates them to Slack. If your source post fits in 4,000 characters, it cross-posts as a single Slack post. If it doesn't, Ferryman keeps the post on platforms where it fits and notes the skip on your Posts page.
Learn more about Slack
Post once, reach every platform — even with different character limits
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