What is the character limit difference between Mastodon and YouTube?

Mastodon allows 500 characters and YouTube allows 5,000.

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

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

Not a direct copy

Cross-posting Mastodon to YouTube: what actually breaks

Not directly. YouTube will not accept a text-only post, so a straight copy is impossible — the post has to be rebuilt for YouTube, not forwarded to it.

Side by side

	Mastodon	YouTube
Characters	500	5,000
Media	optional	a video (required)
Hashtags	2-4 hashtags in CamelCase (#SocialMedia, not #socialmedia) for screen readers	3-5 hashtags in the description, never more than 15 total
Links in body	fine	fine
Needs platform approval	no	yes

What changes, one by one

YouTube will not accept a text-only post

Mastodon posts are frequently text-only. YouTube requires a video on every post, so there is no direct equivalent — you have to attach media before this cross-post is even possible.

You have 4,500 characters you are not using

Mastodon caps at 500 characters, YouTube allows 5,000. Posting the short version verbatim wastes the room YouTube gives you to actually explain the thing.

The hashtag rules are not the same

Mastodon: 2-4 hashtags in CamelCase (#SocialMedia, not #socialmedia) for screen readers. YouTube: 3-5 hashtags in the description, never more than 15 total. Carrying the tag block across is the single most obvious sign of an automated cross-post.

YouTube needs a title you never wrote

YouTube requires a separate title (max 100 characters). Mastodon has no such field, so there is nothing to copy across — it has to be written.

YouTube needs approval, Mastodon does not

You can post to Mastodon today with a credential you generate yourself. YouTube gates posting behind a platform review — see our API approval notes for what that actually takes.

Why copy-paste cross-posting underperforms

Mastodon is community-first; alt text on media is expected, not optional. YouTube is a search engine: the title carries the keyword in the first 40 characters. 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": ["mastodon", "youtube"],
    "text": "Your post",
    "per_platform": {
      "mastodon": { "text": "The Mastodon version" },
      "youtube": { "text": "The YouTube 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 Mastodon to YouTube?: Not directly. YouTube will not accept a text-only post, so a straight copy is impossible — the post has to be rebuilt for YouTube, not forwarded to it.
What is the character limit difference between Mastodon and YouTube?: Mastodon allows 500 characters and YouTube allows 5,000.
How do I post to Mastodon and YouTube at the same time?: With PostWire, one API call publishes to both: POST /api/post with platforms set to ["mastodon","youtube"]. Or one MCP tool call from an AI agent.

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