name: Social Caption Writer
description: Write one platform-native caption from a topic and brand voice, with a front-loaded hook, native length, and a single earned CTA. Use when the user gives a topic (and optionally brand voice or a described image/video) and asks for an Instagram, LinkedIn, X/Twitter, or TikTok caption. Do NOT use when the user wants a dedicated standalone LinkedIn post — use linkedin-post-writer instead; or a multi-post X thread — use tweet-thread-builder instead; or to adapt one existing piece of content into versions for several channels — use cross-platform-reformatter instead.
Social Caption Writer
Turn a topic plus brand voice into one platform-native caption that wins the first line and earns one specific action.
Workflow
- Confirm the platform (Instagram, LinkedIn, X/Twitter, or TikTok). If unstated, ask — every length, shape, and CTA below is platform-specific.
- Pin the brand voice. Use the traits the user gave. If they gave none, ask for 2-3 adjectives and one phrase the brand would never say before writing.
- Check the paired asset. If an image or video is described, write the caption to complement it (don't restate what's visible). If undescribed, ask — the caption's job depends on what it ships with.
- Reject thin or off-brand topics. If there's nothing to say, name that and propose a sharper angle instead of dressing up nothing.
- Write the hook into the first sentence — before the truncation cutoff (~125 chars on Instagram, ~140 on LinkedIn, the first line on X, one breath on TikTok). Lead with tension, a number, a contrarian claim, or a stakes-raising question. Never open with throat-clearing context.
- Fit native length and shape: Instagram 138-150 chars for punchy, or 1-3 tight paragraphs for storytelling; LinkedIn 1300-2000 chars with one-sentence lines and white space between them; X under 280, ideally ~100 so it breathes; TikTok short and curiosity-driven since the video carries the load. Use generous line breaks on Instagram and LinkedIn for mobile reading.
- Carry voice in word choice and rhythm, not adjectives: cut exclamation points for a dry/technical brand; let fragments and asides through for a playful one.
- End with exactly one specific CTA matched to platform behavior — saves/comments on Instagram, thoughtful replies on LinkedIn, reply/repost on X, follow/duet on TikTok. Make it concrete ("Save this for your next launch", not "engage with us"). Reference a link only when there's a real reason to leave the app.
Quality bar
- The first sentence stands alone as a reason to keep reading, with no context preamble before it.
- Length and line-break shape match the chosen platform's range above.
- The brand's voice is detectable in the verbs and rhythm, not just a sign-off.
- Exactly one CTA, specific and matched to how people act on that platform.
- Emojis used as accents, never as punctuation replacements.
Do NOT
- Open with "In today's fast-paced world" or any throat-clearing context.
- Use engagement-bait: "comment YES below", tag-3-friends chains, follow-for-follow — platforms suppress it.
- Keyword-stuff the caption body.
- Stack multiple CTAs or default to "link in bio" with no real reason.
- Write a generic "social" caption that ignores the target platform's reading posture.