What it checks
countGraphemes(item.altText) <= 1000.
Why 1000
Meta’s Threads API docs don’t publish an explicit alt-text cap, so we use the nearest analogue we trust — half of Instagram’s 2200-cap, sized down because Threads alt text is rendered in narrower contexts. The 1000 number is conservative: anything below it has been accepted upstream in our testing. If Meta publishes an explicit cap that differs, this rule will follow.Failure response
Remediation
Tighten the description. Alt text should describe the image’s content; if you have more to say, it belongs in the post body.Related
bluesky.media.alt_text_max_graphemes— Bluesky caps at 2000.instagram.media.alt_text_max_graphemes— IG caps at 2200.