Thread splitter

How this works

• It splits where you would. Paragraph breaks first, then sentence boundaries, then word boundaries. A word is only broken mid-way when the word alone is longer than the limit — which is a URL, in practice.
• Numbering is measured, not guessed. The " 3/12" suffix takes room, and how much depends on the total, which depends on the room. So the split runs twice: once to learn the count, once with the space that count actually needs.
• The limits come from the product. Each network’s limit is read from the same capability table postfast’s composer warns from, so this tool cannot disagree with it.
• Only these four can chain. X, Bluesky, Threads and Mastodon have a native self-reply. Instagram, Facebook and LinkedIn do not, which is why they are not offered here — and why postfast blocks a thread aimed at them rather than publishing the first part alone.
• It runs here, in your browser. Nothing is sent anywhere, stored, or logged.

Common questions

How long can an X thread be?

X sets no limit of its own on how many self-replies chain. postfast accepts a main post plus 25 replies in one composed thread.

Why does numbering change how the text is split?

Because the numbering counts against the limit. A part that fits in 280 characters does not fit once " 7/12" is appended, so the splitter reserves that room up front rather than overflowing.

Can I split for Instagram or LinkedIn?

No, because neither can chain a thread — a reply there is a comment, which does not appear in the feed as part of a chain. Splitting for them would produce parts nothing can publish as a thread.

The other free tools

• Publish Guard

  Paste a post, pick the networks, and see every reason it would be rejected.

• Character counter

  One count, measured against all seven networks’ limits at the same time.

• X API cost calculator

  What X actually charges to publish a post — and why a link costs twenty times more.

• UTM builder

  Build a tagged campaign URL without hand-editing a query string.