platform-voice

name	platform-voice
description	Per-platform tone guides, caption length norms, hashtag etiquette, native-feeling formatting. Used by Terpsichore and Erato.
user-invocable	false
argument-hint	<voice|format|hashtag>
allowed-tools	["Read","Write"]

Platform Voice

Reference for writing copy that reads as native to each platform. Terpsichore uses this to localize a single message into platform-native variants; Erato uses it during initial drafting to avoid one-size-fits-all copy.

Purpose

A platform-native post outperforms a cross-posted one by orders of magnitude in engagement and reach. This skill encodes the voice, length, and formatting expectations of each major surface.

When to use

• Erato is drafting the first version of campaign copy.
• Terpsichore is localizing a copy block for distribution across multiple platforms.
• An atom from editorial-calendar's atomization pass needs platform-specific formatting.
• A repurpose review flags that copy reads off-platform.

Inputs

• Core message (one or two sentences) and the supporting context
• Destination platform(s) from CreativeBrief.channels
• brand_constraints.voice and brand_constraints.tone

Outputs

• One copy variant per destination platform, each compliant with the per-platform spec below
• Hashtag and formatting metadata per variant

Per-platform tone guides

Instagram (feed + Reels captions)

• Voice: warm, visual-first, lifestyle-aware. Captions complement the image; do not narrate it.
• Length: feed captions 138-150 chars before "more" truncation; sweet spot 70-150 chars; long captions (2000-2200 chars max) work for storytelling posts.
• Reels captions: shorter (under 125 chars often best); the video carries the story.
• Hashtags: 3-7 in feed; 0-3 in Reels; place after a line break or in first comment; avoid banned tags.
• Emoji: yes, sparingly, on-brand. Replace bullets with light emoji where tone permits.
• Mention: @brand for credit; do not bait-and-switch tag.
• CTA: "Save this" or "Send to a friend" outperform "Link in bio" for the algorithm.

TikTok

• Voice: native, conversational, low-fi, internet-fluent. No corporate register. Authenticity > polish.
• Caption length: under 150 chars optimal; up to 4000 allowed but rarely read.
• Hooks: text overlay in first frame + caption hook. State the payoff or pose the question immediately.
• Hashtags: 3-5; mix one large (#fyp tier) + 2-3 niche + 1-2 branded. Avoid #fyp alone — algorithm discounts it.
• Sounds: use trending audio when it does not conflict with brand-safety; original sounds for sound-on identity over time.
• Captions on video (burned-in subtitles) are essential; 80%+ of TikTok plays start muted.

X / Twitter

• Voice: punchy, opinionated, conversational. Wit rewarded; cringe punished.
• Length: under 280 chars per tweet; threads for depth (8-12 tweets max).
• Hooks: first 7 words decide whether the tweet gets the click or scroll-past.
• Hashtags: 0-2 max; usually none. Hashtags reduce reach on X.
• Mentions: @ a person only when they would actually want the tag.
• Reply game: replies and quote-tweets in the brand's niche compound faster than original posts.
• Avoid: corporate platitudes, threaded ads, "a thread" announcements before delivering value.

LinkedIn

• Voice: professional but human; first-person; specific over generic; insight over inspiration.
• Length: 1300-1900 chars optimal for organic reach (post truncates around 210 chars; "see more" click is the engagement signal).
• Formatting: short paragraphs (1-2 sentences each); white space; occasional bullet via line breaks; avoid markdown (not rendered).
• Hashtags: 3-5 at the end; mix of broad and niche.
• CTA: ask a question that invites comment; comments drive reach more than likes.
• Avoid: humble-brags, generic career advice, AI-generated platitudes (the platform is fatigued).

YouTube (titles + descriptions + community posts)

• Titles: 60 chars max before truncation; lead with the payoff; numbers and curiosity gaps perform; avoid clickbait that the video does not deliver.
• Descriptions: 200-500 words; first 150 chars matter most (above-the-fold); include keyword variants naturally; add timestamps as chapters; include CTAs and links at the bottom.
• Tags: less important than they used to be; still include 5-15 relevant.
• Community posts: 200-500 char polls, image posts, text updates; engagement here lifts video impressions.
• Shorts: title is the hook; description short; the video is everything.

Threads

• Voice: conversational, lower-stakes than X; more personal, less aggressive.
• Length: 500 chars per post; threads via reply chains; sweet spot 100-300 chars.
• Hashtags: one per post max; often skipped.
• Replies: weight even higher than X; the platform's algorithm rewards conversation.
• Cross-posting from IG works but native posts do better; rewrite, do not paste.

Substack / newsletter

• Voice: long-form, essayistic, personal. Subscribers expect a voice; deliver one.
• Length: 600-1800 words common; consistent length per series.
• Subject line: 30-50 chars; specific over clever; A/B test if volume allows.
• Pre-header: complements (does not repeat) subject line.
• Structure: lead with the most surprising sentence; deliver in body; close with a single CTA.
• Hashtags: not applicable.

Caption length cheat sheet

Platform	Sweet spot	Hard cap
Instagram feed	70-150 chars	2200 chars
Instagram Reels	<125 chars	2200 chars
TikTok	<150 chars	4000 chars
X / Twitter	<240 chars (room for RT)	280 chars
LinkedIn	1300-1900 chars	3000 chars
YouTube title	<60 chars	100 chars
YouTube description	200-500 words	5000 chars
Threads	100-300 chars	500 chars
Substack subject	30-50 chars	150 chars

Hashtag etiquette

• IG: 3-7 in feed, 0-3 in Reels; mix branded + niche + broad; avoid banned tags (Instagram silently suppresses).
• TikTok: 3-5; one broad + 2-3 niche + 1-2 branded; avoid #fyp alone.
• X: 0-2; usually zero; hashtags reduce reach.
• LinkedIn: 3-5 at end; mix of broad (#leadership, #marketing) and niche (#b2b-saas-pricing).
• Threads: 0-1.
• YouTube: in description, 3-15; first 3 show under title.
• Pinterest: 0-5 hashtags but use the description field for keyword-rich copy instead.

Never invent campaign hashtags that nobody will type. Use branded tags only when they will be re-used across many posts.

Native-feeling formatting

• Match the platform's native punctuation rhythm — TikTok captions often skip periods; LinkedIn uses single-line paragraphs; X uses em-dashes and line breaks.
• Avoid markdown on platforms that do not render it (LinkedIn, X, Instagram). Use unicode bullets only when on-brand.
• Emoji: brand-dependent; never replace nouns with emoji on B2B platforms.
• Line breaks: load-bearing; previewable above-the-fold space is the first sentence on every platform.
• Subtitles on video: required for TikTok, Reels, YouTube Shorts; default for Feed.

Procedure

1. Read the core message and destination platforms.
2. For each platform, draft a variant honoring the voice and length cheat sheet above.
3. Append platform-correct hashtags; verify against banned-tag lists where relevant.
4. Add subtitle text for any video destination.
5. Run brand-safety guardrail check on every variant.
6. Emit copy block per destination; hand to Terpsichore for scheduling.
7. After publication, log engagement per variant via eights.memory.remember(tags=["platform","voice","performance"]) so future drafts inherit what works.

Failure modes / escalation

• Cross-posted copy reads off-platform — rewrite; do not approve.
• Hashtag in banned list — substitute; verify before publish (lists shift).
• Voice conflict between platforms (e.g. exec wants the LinkedIn voice on TikTok) — escalate to Calliope; document the trade-off.

References

• Brand guardrails: brand-safety
• Atom inventory and cadence: editorial-calendar
• Memory tags: platform, voice, performance