---
name: "video_thumbnails"
description: "Design video thumbnails that win the click: composition, short-text rules, contrast, CTR basics, and testing (YouTube Test & Compare). Triggers when someone needs a thumbnail designed, critiqued, or iterated — or asks how to raise video click-through rate."
---

# Video Thumbnails

## Purpose
Turn a video's promise into a thumbnail that earns the click against a feed of
competitors. Used two ways: **design** (produce concepts, mockups, and a final
spec for the image generator) and **critique** (score an existing thumbnail and
prescribe fixes). Facts below are from YouTube Help, verified 2026-09-20; full
citations live in `references/design-playbook.md`.

## Workflow
1. **Lock the promise first.** One line: what the viewer gets from this video.
   Write the video title before touching the thumbnail — the thumbnail's job is to
   create tension with the title, not repeat it. Never put title words on the
   thumbnail.
2. **Generate 3 concepts**, each with ONE hook (face + strong emotion, before/after,
   big number, versus, curiosity gap — the eye sees the outcome but not the cause,
   or a pattern interrupt that breaks the niche's visual convention). One hook per
   thumbnail; stacking hooks dilutes them.
3. **Compose each concept**: one dominant focal subject (rule of thirds), one short
   headline block (3–5 words, bold sans-serif, high stroke), a background that
   contrasts the subject, and negative space so it breathes. Keep it simple —
   complexity loses to clarity at feed size.
4. **Validate mechanically.** For each concept run
   `bin/thumb_mockup.py --spec spec.json --out mock.png` (renders a labeled layout
   mockup plus a 160px-wide squint preview — the size text must read at on mobile)
   and `bin/text_contrast.py --fg FFFFFF --bg 101418` for every text/background
   pair (pass bar: contrast ratio ≥ 3.0 for large thumbnail text, aim ≥ 4.5).
   If the squint preview is unreadable or the contrast fails, fix the concept —
   never ship it.
5. **Pick a winner by critique, then write the final spec** for the image tool:
   subject description + emotion/pose, background, exact headline text, color
   palette (hex), and what must NOT appear (no title words, no logos clutter,
   no misleading visuals).
6. **Export to platform spec**: 1280×720, 16:9, JPG or PNG, ≤ 2 MB (safe on every
   upload path). YouTube Help also lists 3840×2160 as recommended with a higher
   desktop limit, but 1280×720 renders everywhere and never gets rejected.
7. **Test, don't guess.** If YouTube Studio's **Test and Compare** is available:
   upload up to 3 meaningfully different variants (not font-size tweaks), let it
   run to completion (~2 weeks max), and accept that the winner is chosen by
   **watch-time share, not CTR**. Otherwise: swap thumbnails manually only after
   the video stabilizes (7–14 days), then compare impressions CTR on Home/Suggested
   in comparable 24–48h windows.
8. **Read the numbers honestly.** Per YouTube Help, half of all channels/videos sit
   at 2–10% impressions CTR — compare a video against similar videos on the same
   channel, not against a universal benchmark. High CTR + falling average view
   duration = clickbait signal; that thumbnail is hurting the channel.

## Output Contract
- **Design task**: 3 concept cards (hook, layout, headline text, palette) +
  mockup PNGs + squint previews + a chosen final with a copy-paste image-generation
  prompt + export spec + test plan (Test & Compare variants or manual-swap schedule).
- **Critique task**: scorecard on focal clarity / text legibility at feed size /
  color contrast / title synergy / clickbait risk, each with a concrete fix
  ("headline fails 160px test → cut to 3 words and move to lower third").

## Operating Rules
1. **Honesty beats clickbait.** The thumbnail must depict what the video actually
   delivers. Misleading thumbnails are prohibited by YouTube's deceptive-practices
   policy and YouTube Help explicitly says chasing CTR with clickbait lowers
   recommendations. Never propose one.
2. **Never repeat the title on the thumbnail.** Wasted pixels; the packaging unit is
   thumbnail + title together.
3. **No concept ships without a squint preview and a contrast check.** The tools in
   `bin/` are the gate, not the taste.
4. **Facts about the platform are verified, not remembered.** Specs, CTR ranges, and
   Test & Compare mechanics in this skill were verified against YouTube Help on
   2026-09-20 — see `references/design-playbook.md`. If the platform changes,
   re-verify before asserting.