Create social posts, newsletters, and marketing copy that respects platform mechanics — truncation points, algorithm signals, and hook physics — not just "good writing."

When to Use

Social posts (X/Twitter, LinkedIn, Instagram feed, Instagram Stories, TikTok captions, Threads)
Writing captions for social media posts
Writing hooks for posts and content
Newsletters, blog posts, content calendars, cross-platform repurposing
Content repurposing ("turn this into multiple posts", "repurpose this blog post")
Social media strategy and content planning

When NOT to Use

Cold outreach (cold-email-writer) · Paid ad copy (ad-creative) · Research reports (deep-research) · SEO audits (seo-auditor)

Step 1: Voice Analysis

Ask for 3-5 existing posts. Extract: avg sentence length, contraction usage, emoji density, POV (I/we/you), signature phrases. If none exist, ask for 2 creators they want to sound like and use webFetch to pull recent posts as voice reference.

Step 2: Platform Mechanics (2025-2026 Specs)

LinkedIn — 3,000 char max, but truncation is what matters

"...see more" cutoff: ~140 chars desktop, ~110 chars mobile. 57%+ of LinkedIn traffic is mobile — write the hook for 110 chars.
Algorithm weights: comments count ~2x likes; dwell time is a primary signal; first 60-120 min engagement velocity determines reach ceiling.
Optimal length: 800-1,000 chars (not 3,000). Short paragraphs (1-2 lines) + white space increase dwell time.
Structure: Hook (110 chars, no throat-clearing like "I wanted to share...") → story/insight → single question CTA. Reply to every comment in the first hour to extend the test window.
Hashtags: 3-5 max, at the very end. LinkedIn deprioritized hashtag discovery.

X/Twitter — 280 chars (free), 25,000 chars (Premium)

Long posts on Premium truncate at ~280 chars in the feed — the hook rule still applies.
Thread structure: Tweet 1 = the full promise ("How I went from X to Y in Z — thread 🧵"). Each tweet must stand alone for retweets. Last tweet = CTA + loop back to tweet 1.
Line breaks double engagement vs. wall-of-text.

Instagram Feed — 2,200 char caption, ~125 chars visible before "...more"

Hashtags: 3-5, not 30. Instagram's @creators account officially reversed the old advice; 20+ hashtags now reads as spam and can suppress reach. Put them inline or at the end, not in a comment.
First line = hook. Emoji as bullet points scan faster than dashes on mobile.
Format: Square (1080×1080) or portrait (1080×1350, 4:5 — outperforms square on CTR).

Instagram Stories — 1080×1920, 9:16

Stories are a fundamentally different medium from feed posts. Treat them as such.

Key differences from feed

Stories are ephemeral and sequential — viewers tap through in 2-3 seconds. There is no caption to read. The visual is the entire message.
Stories are better for two-way interactions (polls, questions, DMs) than for broadcasting.
Feed posts have copy doing the heavy lifting. Stories must work without it.

Safe zones — mandatory

| Zone | Range | Why |

|---|---|---|

| Top dead zone | Top 14% (~270px) | Profile name, mute, close button UI |

| Bottom dead zone | Bottom 20% (~380px) | "Send message" bar + swipe-up area |

| Safe core|14% – 80% from top | All content must live here |

Never place any text, logo, CTA, or key visual outside the safe core.

Story formats by content type

| Content angle | Best story format | Why |

|---|---|---|

| Pain point | Single frame, stripped to one-liner | Needs immediate gut impact — no room for buildup |

| Educational | Poll (two-option) | Polls get 3× more taps than passive stories; drives return for "reveal" |

| Feature/product | 3-frame sequence: Problem → Solution → Result | Complex message needs beats; tap-through is an algorithm signal |

| Relationship/split concept | Vertical split visual | 9:16 is naturally tall — a top/bottom split reads instantly |

| Tips list | One tip per frame (e.g., "Tip 1 de 3") | Breaks up information; each frame drives tap-through to next |

Story copy rules

Strip feed copy to its absolute core. One line, not a paragraph.
The hook becomes the entire visual headline — make it 9-12vw on screen and impossible to miss.
CTAs live in the bottom safe zone (72-78vh) as a full-width strip or pill — not scattered across the frame.
Progress indicators ("1 / 3", three dots) signal sequence to viewers and reduce drop-off between frames.

Poll stories

Two options, both plausible — avoid obvious right answers.
Create a reason to return: "Mañana revelamos el promedio real" drives next-day traffic.
Benchmark: 20-40% response rate on engaged audiences.

Multi-frame sequences

Each frame must have a clear progress indicator so viewers know there's more.
Each frame must have a tap hint (e.g., "Toca para continuar →") except the last.
Last frame ends with a CTA, not a tap hint.
File naming: story3a.html,story3b.html,story3c.html for the 3 frames of Story 3.

Same angle, different execution — never just resize a feed post

| Feed post | Story adaptation |

|---|---|

| Pain point with supporting copy | Strip to the one-liner only — huge on screen, nothing else |

| Educational post with data | Turn into a poll question — let the audience engage, reveal answer next day |

| Feature walkthrough | 3-frame sequence: Frame 1 = problem, Frame 2 = solution stat, Frame 3 = result UI |

| Relationship/split concept | Vertical split (top half / bottom half) unified at the seam |

| Tips list (3 items) | 3 separate frames, one per tip, "Tip 1 de 3" format |

TikTok captions — 4,000 chars (up from 2,200)

TikTok is now a search engine — ~40% of Gen Z searches here before Google. Front-load keywords in the caption for TikTok SEO. The caption is indexed; use it for terms your video doesn't say out loud.

TikTok Video Production (Composited Short-Form Video)

The skill CAN produce TikTok-format video (1080×1920, 9:16) using FFmpeg + AI-generated clips. This is not just captions — it is full video production.

API capability disclosure — mandatory before starting: When producing TikTok video, always inform the user upfront that two quality tiers exist:

Without an external API (default): AI-generated clips via the built-in media-generation tool — cinematic-style footage, good for most use cases, no extra setup or cost.
With an external API (higher quality): Services like Runway Gen-3, Pika, or Kling can produce significantly more realistic and controllable footage, but require a paid API key from the user.

Always present both options and ask which they prefer before generating any clips. Never silently call a paid external API. Never assume the user knows these options exist — they usually don't.

Production workflow

Write a scene brief: 3-5 scenes, each with a visual prompt, text overlays, and duration (6-8s per scene is ideal). Total target: 20-30s.
Generate AI clips using the media-generation skill — one prompt per scene, 9:16 format.
Prepare brand fonts and assets (logo PNG).
Compose with FFmpeg using a Node.js script (.cjs).
Output to client/public/videos/— served at/videos/ on the Replit domain.

FFmpeg in Replit NixOS

FFmpeg v6+ is available. Locate it: ls /nix/store/*ffmpeg-full*/bin/ffmpeg 2>/dev/null | head -1
Run via execFileSync('ffmpeg', args) — do NOT use shell string commands (escaping nightmare).

Font handling — Inter (or any Google Font)

Download the GitHub release zip: https://github.com/rsms/inter/releases/download/v4.0/Inter-4.0.zip
Extract TTF files using Node.js zlib.inflateRawSync()— do not assumeunzip or Python are available.
Write to /tmp/tiktok/fonts/Inter-Black.ttf,Inter-Bold.ttf,Inter-Regular.ttf.
Always use the brand font. DejaVu (FFmpeg's fallback) looks wrong on brand content.

FFmpeg filter techniques


# Dark overlay for text readability on top of any clip

drawbox=x=0:y=0:w=iw:h=ih:color=0x000000@0.50:t=fill

# Text overlay — use execFileSync (array args), never shell strings, so UTF-8 works directly

drawtext=fontfile='/path/Inter-Black.ttf':fontsize=110:fontcolor=0xffffff:x=(w-text_w)/2:y=700:text='Tu texto aqui'

# Logo overlay — scale first, split for N scenes, then overlay each

[logoInput]scale=185:-1,split=4[logo0][logo1][logo2][logo3]

[clip_pre][logo0]overlay=x=65:y=72:format=auto[clip_out]

# Xfade transition between clips (0.4s fade)

[c0][c1]xfade=transition=fade:duration=0.4:offset=5.6[v01]

# Audio: music bed, trim to total duration, fade in/out

[musicInput]atrim=0:24.8,afade=t=in:st=0:d=1.0,afade=t=out:st=23.0:d=1.8[aout]

Scene structure that works (4-scene formula)

|---|---|---|---|

| CTA | Positive resolution, couple/family | Download prompt, URL badge, attribution | 8s |

Overlay composition rules

Dark overlay alpha: 0.40–0.55 for clips that need text; 0.35–0.45 for product/app clips (show them).
Text hierarchy: headline in brand color or white at 110-130px (Inter Black), body at 50-70px (Inter Bold), captions at 36-44px (Inter Regular).
Logo: top-left corner, ~185px wide, every scene — use scale=185:-1,split=N.
All content within 140px–1780px vertical (safe zone same as Stories: avoid top 14% and bottom 20%).

Output settings (always use these exactly)


-c:v libx264 -preset fast -crf 18 -pix_fmt yuv420p -movflags +faststart -c:a aac -b:a 192k

Music licensing

If using CC BY music (e.g., Kevin MacLeod), attribution must appear IN the video (small text overlay, last scene), not just in the caption. Caption-only attribution does not satisfy CC BY for video.
Recommended free source: freemusicarchive.org, filter by CC BY.

Canvas embedding

Always resolve the domain with echo $REPLIT_DOMAINS before setting a canvas video shape URL. Never hardcode a domain — Replit domains change between sessions.
Video shape URL format: https://<domain>/videos/filename.mp4

Newsletters — Optimize for clicks, not opens

**Apple Mail Privacy Protection (MPP) inflates open rates by ~18 percentage points.**Apple Mail is ~46% market share and pre-fetches tracking pixels. A "42% open rate" in 2025 ≈ a 24% open rate in 2020.Track click rate (benchmark: ~2%) and CTOR (10-20%) instead.
Subject line: 30-50 chars. Avoid "Free," ALL CAPS, multiple "!!!" — spam filter triggers. B2B: longer, specific subject lines outperform short clever ones.
Preview/preheader text: adds ~6pp to open rate when used — but Gmail's Gemini now auto-generates previews, so don't rely on controlling it. Write the first sentence of the body as a second hook.
One primary CTA. Every additional CTA cuts click rate.

Step 3: Hook Formulas (Named Patterns)

Don't say "write a hook" — pick a pattern:

| Pattern | Template | Why it works |

|---|---|---|

| Contrarian | "Everyone says X. Here's why that's wrong." | Cognitive dissonance forces resolution |

| Curiosity gap | "I tried X for 30 days. Day 17 broke me." | Open loop — brain needs closure |

| Specificity signal | "$47,212 in 90 days. Here's the exact stack." | Odd numbers read as true, round numbers read as marketing |

| Negative hook | "3 mistakes that cost me [outcome]" | Loss aversion > gain seeking |

| Callout | "If you're a [role] still doing X, read this." | Self-selection = higher-intent readers |

| Slippery slope | "It started with one Slack message." | Narrative momentum |

| Permission | "Unpopular opinion: [take]" | Pre-frames disagreement as expected |

Banned openers: "I'm excited to share," "Hey everyone," "As a [title]," "In today's fast-paced world."

Step 4: Repurposing Waterfall

One long-form piece → 8+ assets:

Blog post (1,500 words) →
X thread (extract each H2 as a tweet, intro = hook) →
LinkedIn post (pick the single most contrarian point, 800 chars) →
LinkedIn carousel (each H2 = 1 slide; carousels get highest dwell time) →
Newsletter section (add personal context + behind-the-scenes) →
Instagram feed post (hook + 3-5 supporting points, 1080×1080 or 1080×1350) →
Instagram Story (strip the feed hook to a single line, or turn the educational point into a poll) →
TikTok/Reel script (the hook + the #1 takeaway in 30 sec)

Key rule for Stories in the waterfall: same angleas the feed post, completely differentexecution. Never just crop or resize a feed post into a Story — re-author it according to the story format table above.

Build repurposing scripts in Python when batch-processing: parse markdown H2s → split into platform templates → enforce char limits programmatically.

Content Frameworks

PAS (Problem → Agitate → Solve) — best for conversion-focused posts
BAB (Before → After → Bridge) — best for transformation stories
AIDA (Attention → Interest → Desire → Action) — best for launches
SLAP (Stop → Look → Act → Purchase) — best for short-form (Reels/TikTok captions)

Validation

Before delivering, verify:

Char counts against platform limits (count programmatically, don't eyeball)
Hook fits in the truncation window (110 chars for LinkedIn mobile, 125 for Instagram feed)
No banned openers
One CTA per piece
For Stories: all content confirmed inside the 14%–80% safe zone

Limitations

Cannot post to platforms or access analytics
Cannot generate static images directly — use the media-generation skill for images; use the ad-creative skill for HTML/CSS visual story designs
CAN produce composited short-form video (TikTok/Reels) via FFmpeg + AI clip generation — see TikTok Video Production section above
Paid external video APIs (Runway, Pika, Kling) require user consent and their own API key before use
Voice matching quality scales with example count