threads.media.count_max - letmepost.dev

What it checks

media.length <= 20. Threads is the most permissive carousel of the platforms supported here — 20 children, mixed images and videos. The minimum carousel size is 2; below that, single-image or single-video shapes apply (see threads.text.required for the post-shape decision tree).

Failure response

{
  "error": {
    "code": "preflight_failed",
    "rule": "threads.media.count_max",
    "platform": "threads",
    "message": "Attached 25 media items; Threads allows at most 20 per carousel.",
    "remediation": "Reduce to 20 items or fewer, or split into multiple posts."
  }
}

Remediation

Cap at 20. For longer galleries, split into a thread — Threads’s reply UX is solid, and each reply can hold 20 more.

threads.media.alt_text_max_graphemes
instagram.media.count_max — IG caps the same shape at 10.