What is the character limit difference between X and Mastodon?

X allows 280 characters and Mastodon allows 500.

How do I post to X and Mastodon at the same time?

With PostWire, one API call publishes to both: POST /api/post with platforms set to ["x","mastodon"]. Or one MCP tool call from an AI agent.

Works, with rewrites

Cross-posting X to Mastodon: what actually breaks

You can, but not by copying the text across: 2 things change between X and Mastodon, starting with the hashtag rules are not the same. Below is exactly what breaks and what to do instead.

Side by side

	X	Mastodon
Characters	280	500
Media	optional	optional
Hashtags	1-2 hashtags, zero is fine	2-4 hashtags in CamelCase (#SocialMedia, not #socialmedia) for screen readers
Links in body	suppress reach	fine
Needs platform approval	yes	no

What changes, one by one

The hashtag rules are not the same

X: 1-2 hashtags, zero is fine. Mastodon: 2-4 hashtags in CamelCase (#SocialMedia, not #socialmedia) for screen readers. Carrying the tag block across is the single most obvious sign of an automated cross-post.

Mastodon lets you put the link back in

X penalises links in the body, so posts written for it park the URL elsewhere. On Mastodon links in the body are fine — putting it back is free reach.

Why copy-paste cross-posting underperforms

X is one hook and nothing else — opinionated, conversational, over in a breath. Mastodon is community-first; alt text on media is expected, not optional. Those are different jobs, so the same words cannot do both well — and every algorithm here demotes text that obviously was not written for it. The fix is not to skip cross-posting; it is to send a native version to each network.

Publish to both in one call

curl -X POST https://postwire.io/api/post \
  -H "Authorization: Bearer $POSTWIRE_API_KEY" \
  -H "Content-Type: application/json" \
  -d '{
    "platforms": ["x", "mastodon"],
    "text": "Your post",
    "per_platform": {
      "x": { "text": "The X version" },
      "mastodon": { "text": "The Mastodon version" }
    }
  }'

PostWire's /api/generate writes those per-platform versions for you from a single prompt, respecting every limit in the table above. From an AI agent it is one MCP tool call.

Get an API key free →

Questions people actually ask

Can I cross-post from X to Mastodon?: You can, but not by copying the text across: 2 things change between X and Mastodon, starting with the hashtag rules are not the same. Below is exactly what breaks and what to do instead.
What is the character limit difference between X and Mastodon?: X allows 280 characters and Mastodon allows 500.
How do I post to X and Mastodon at the same time?: With PostWire, one API call publishes to both: POST /api/post with platforms set to ["x","mastodon"]. Or one MCP tool call from an AI agent.

Other pairs: Mastodon to X · all combinations · which APIs need approval