What is the character limit difference between Facebook and Mastodon?

Facebook allows 2,000 characters and Mastodon allows 500.

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

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

Works, with rewrites

Cross-posting Facebook to Mastodon: what actually breaks

You can, but not by copying the text across: 2 things change between Facebook and Mastodon, starting with you lose 1,500 characters. Below is exactly what breaks and what to do instead.

Side by side

	Facebook	Mastodon
Characters	2,000	500
Media	optional	optional
Hashtags	1-3 hashtags	2-4 hashtags in CamelCase (#SocialMedia, not #socialmedia) for screen readers
Links in body	fine	fine
Needs platform approval	yes	no

What changes, one by one

You lose 1,500 characters

Facebook allows 2,000 characters; Mastodon caps at 500. A post written to Facebook's length gets truncated — usually mid-sentence — unless it is rewritten, not trimmed.

The hashtag rules are not the same

Facebook: 1-3 hashtags. 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.

Why copy-paste cross-posting underperforms

Facebook is warm and community-toned; 40-80 characters peaks engagement. 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": ["facebook", "mastodon"],
    "text": "Your post",
    "per_platform": {
      "facebook": { "text": "The Facebook 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 Facebook to Mastodon?: You can, but not by copying the text across: 2 things change between Facebook and Mastodon, starting with you lose 1,500 characters. Below is exactly what breaks and what to do instead.
What is the character limit difference between Facebook and Mastodon?: Facebook allows 2,000 characters and Mastodon allows 500.
How do I post to Facebook and Mastodon at the same time?: With PostWire, one API call publishes to both: POST /api/post with platforms set to ["facebook","mastodon"]. Or one MCP tool call from an AI agent.

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