AI captions written for each platform's limits
Voxpanda writes one caption per platform from a single content idea, and every caption is checked against that platform’s character limit before it enters the publishing queue. Captions are one step of Voxpanda, an AI social media manager that also makes the post image, schedules it, and replies to comments and DMs within each platform’s official API rules.
What goes into a caption
The caption writer uses five inputs:
- the hook you selected
- your brief
- your brand tone
- your call to action
- the language, English or Indonesian
The first line usually comes from the hook bank with per-brand scores, which ranks hooks by how they performed on your account.
What Voxpanda returns for each platform
For every connected platform, the AI returns:
- caption, sized for that platform
- hashtags, within the platform’s limit
- first comment, optional
- thread parts, when the text is split into a thread
- alt text for the image
Character limits per platform
Each caption is validated on the server against the limit of its platform before the post is queued.
| Platform | Text limit | Extra rule |
|---|---|---|
| 2,200 characters | up to 30 hashtags and 20 @ tags; Voxpanda targets 3 to 8 hashtags | |
| Facebook Page | 63,206 characters | 0 to 3 hashtags |
| Threads | 500 characters per post | longer text is split into a thread |
| TikTok | 2,200 characters | you can edit the caption before posting, as TikTok requires |
| X | 280 characters for non-Premium accounts | a link raises the post price |
| YouTube | title 100 characters, description 5,000 bytes | |
| 3,000 characters | AI content label required | |
| Bluesky | 300 graphemes |
You can test a draft against these limits with the free social media character counter.
Auto-shorten, once
If a caption goes over its limit, Voxpanda shortens it automatically one time. If the shorter version still fails, the caption is flagged and waits for your edit. A caption that breaks a platform limit is not queued.
On X, a post with a link costs more than a post without one: $0.20 instead of $0.015 under X’s pay-per-use pricing, checked 13 October 2026. In Voxpanda Credits, an X post costs 3 credits without a link and 35 credits with one.
Brand voice from approved captions
Voxpanda learns your style from captions you have approved. The 10 most recent approved captions for a brand become examples for the next caption. As you edit and approve, the examples change, and new captions follow your latest wording.
Each brand has its own examples. An agency running several client brands does not mix one client’s voice into another’s.
Platform rules that shape captions
- Threads: text over 500 characters becomes a thread.
- TikTok: you can edit the caption before the post is published, which is part of TikTok’s Content Sharing Guidelines.
- LinkedIn: AI-generated content must carry a label under LinkedIn’s Developer AI Policy (14 January 2026). LinkedIn is used for publishing only.
An Instagram caption follows the same pipeline as the others, with a 2,200 character limit and 3 to 8 hashtags as the target. Limits for every platform are collected in the article on caption length and posting limits per platform.
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Questions
Does Voxpanda write a different caption for each platform?
Yes. One content idea produces a separate caption for each connected platform, with its own length, hashtags and format.
What happens when a caption is too long?
Voxpanda shortens it automatically once. If it is still over the platform limit, the caption is flagged for you to edit before it enters the queue.
How does the AI learn my brand voice?
Your approved captions become style examples for your brand. Voxpanda uses the 10 most recent approved captions as examples when it writes the next one.
Is an AI caption generator the same as an AI social media manager?
No. A caption generator writes text and stops there. An AI social media manager also makes the image, schedules the post and replies to comments and DMs.
Does Voxpanda label AI-written posts on LinkedIn?
Yes. LinkedIn requires a label on AI-generated content, so Voxpanda adds one to LinkedIn posts.