| YouTube | ||
|---|---|---|
| Characters | 5,000 | 2,200 |
| Media | a video (required) | a photo or video (required) |
| Hashtags | 3-5 hashtags in the description, never more than 15 total | max 5 hashtags at the END of the caption |
| Links in body | fine | fine |
| Needs platform approval | yes | yes |
YouTube allows 5,000 characters; Instagram caps at 2,200. A post written to YouTube's length gets truncated — usually mid-sentence — unless it is rewritten, not trimmed.
YouTube: 3-5 hashtags in the description, never more than 15 total. Instagram: max 5 hashtags at the END of the caption. Carrying the tag block across is the single most obvious sign of an automated cross-post.
YouTube expects 16:9 landscape (Shorts 9:16). Instagram expects 9:16 for Reels, 1:1 or 4:5 for feed. The same file will be letterboxed or cropped.
YouTube is a search engine: the title carries the keyword in the first 40 characters. Instagram is built for short captions — under 100 characters is rewarded. 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.
curl -X POST https://postwire.io/api/post \
-H "Authorization: Bearer $POSTWIRE_API_KEY" \
-H "Content-Type: application/json" \
-d '{
"platforms": ["youtube", "instagram"],
"text": "Your post",
"per_platform": {
"youtube": { "text": "The YouTube version" },
"instagram": { "text": "The Instagram 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.
Other pairs: Instagram to YouTube · all combinations · which APIs need approval