Postsiva validates text length before posting. Over-limit text returns HTTP 422 with the platform name and character count.
Primary limits (captions / post text)
| Platform | Limit | Field(s) | Post types |
|---|
| LinkedIn | 3,000 | default_text, linkedin_text, linkedin_page_texts | Text, image, video, carousel |
| Facebook | 63,206 | default_text, facebook_page_texts | Text, image, video, carousel |
| Threads (text) | 500 | default_text, threads_text | Text only |
| Threads (caption) | 2,200 | Caption on image, carousel, video | Image, carousel, video |
| Instagram | 2,200 | default_text, instagram_text | Image, carousel, video |
| TikTok | 2,200 | default_text, tiktok_text | Video, image, carousel |
| Bluesky | 300 | default_text | Text, image, carousel, video |
| YouTube | — | See title/description below | Video only |
Secondary limits (titles / descriptions)
| Platform | Field | Limit |
|---|
| YouTube | youtube_title / default_text (title) | 100 |
| YouTube | youtube_description | 5,000 |
| Pinterest | pinterest_text (pin title) | 100 |
| Pinterest | pinterest_description | 500 |
| TikTok (photo) | tiktok_title | 90 UTF-16 code units |
Multi-platform posting
When posting to multiple platforms, each platform is validated independently. A caption valid for LinkedIn (3,000) may fail on Bluesky (300):
{
"platforms": ["linkedin", "bluesky"],
"default_text": "A 400-character caption..."
}
422 for Bluesky even if LinkedIn would succeed.
Use platform overrides to send different lengths per destination:
threads.threads_text, instagram.instagram_text, etc.
Example: platform-specific text
{
"platforms": ["linkedin", "threads", "bluesky"],
"default_text": "Full LinkedIn article-style post with details...",
"threads": {
"threads_text": "Medium-length Threads post under 500 chars."
},
"bluesky": {}
}
default_text to 300 chars or add a shorter override in a pre-processing step.
{
"detail": "Max text character limit for threads is 500. Received 612 characters in threads_text/default_text."
}
{
"detail": "Max text character limit for linkedin is 3000. Received 3100 characters in linkedin_page_texts[108813535]."
}
Quick reference by use case
| Use case | Safe default length |
|---|
| Cross-post to all text platforms | 300 (Bluesky floor) |
| LinkedIn + Facebook only | 3,000 |
| Threads text post | 500 |
| Instagram / TikTok caption | 2,200 |
| YouTube title | 100 |
| Pinterest pin title | 100 |
Platforms overview
All eight platforms
HTTP errors
422 validation errors