Generate a YouTube thumbnail artifact — a 1280×720 HTML canvas optimized for legibility at small sizes (mobile feed, sidebar suggestions, search results). Reads ./design/<brand-slug>/DESIGN.md, tokens.css, and components.html. Triggers include "youtube thumbnail for X", "thumbnail for [video title]", "yt thumb", "/youtube-thumbnail".
Installation
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Generate a YouTube thumbnail artifact — a 1280×720 HTML canvas optimized for legibility at small sizes (mobile feed, sidebar suggestions, search results). Reads ./design/<brand-slug>/DESIGN.md, tokens.css, and components.html. Triggers include "youtube thumbnail for X", "thumbnail for [video title]", "yt thumb", "/youtube-thumbnail".
Skill: youtube-thumbnail
Produces a pixel-exact 1280×720 HTML canvas. The defining constraint: it must read clearly at 240×135px (typical mobile feed thumbnail) — not just at full size. Bias toward fewer words, larger type, higher contrast than other platform skills.
When to use
User has (or is about to publish) a YouTube video and wants a thumbnail asset
A DESIGN.md exists for the brand
Inputs
Required: brand slug, video title (the ACTUAL video title, not the on-thumbnail text)
Required: thumbnail text — the 2–4 words that go ON the image (this is NOT the video title; it's the visual hook)
1. Video title (full title that goes in YouTube's title field)
2. Thumbnail text — 2–4 words MAX that appear ON the image. This is your visual hook, not your title.
Examples: "Built it wrong" / "Faster than you'd think" / "Why I quit Vim" / "Day 47"
3. Optional episode/series marker (e.g. "EP. 12" or "PART 3 / 5")
4. Optional supporting micro-text under the hook (max 6 words)
If the user gives you 8+ words for thumbnail text, push back: "That's too many for legibility at mobile size. Pick the 3–4 words that carry the hook." Don't proceed until they agree.
3. Pick variation — ARCHITECTURE FIRST
Pick ONE archetype before any other axis. YouTube thumbnails have specific archetypes that work at small sizes; pick from these.
Architecture archetype (pick FIRST):
text-only — the hook is the entire artifact. No marker, no mark, no rules. Default for maximum legibility.
single-word — one massive word fills 70%+ of canvas; everything else absent.
Type pressure: monolithic-display (one huge word) | stacked-words (words on own lines) | display-with-mono-caption
Color usage: single-accent-block | inverted-canvas | monochrome | duotone-split
Avoid: faces, arrows pointing at things, red circles around things, "MIND BLOWN" energy. Type-led restraint is the differentiator.
Cross-artifact rule: different archetype than the brand's most recent artifact (check ./design/<brand-slug>/artifacts/).
4. Generate the canvas HTML
<!DOCTYPE html><htmllang="en"><head><metacharset="utf-8"><title><Brand> — YouTube — <videotitle></title><linkrel="preconnect"href="https://fonts.googleapis.com"><linkrel="preconnect"href="https://fonts.gstatic.com"crossorigin><linkrel="stylesheet"href="https://fonts.googleapis.com/css2?family=<families>&display=swap"><style>/* Embed tokens.css verbatim */
<contents of tokens.css>
html, body { margin: 0; padding: 0; background: #2a2a2a; min-height: 100vh; display: grid; place-items: center; font-family: var(--type-body-md-family); }
.canvas {
width: 1280px;
height: 720px;
background: var(--color-surface);
color: var(--color-ink);
position: relative;
overflow: hidden;
padding: var(--space-2xl);
box-sizing: border-box;
display: flex;
flex-direction: column;
/* Justification per layout choice */
}
/* The hook text — MUST be massive. Use clamp() with high min/max */.hook {
font-family: var(--type-display-xl-family);
font-weight: 700; /* even if display-xl is 600, push to 700 here for thumbnail weight */letter-spacing: -0.025em;
line-height: 0.95;
margin: 0;
font-size: clamp(140px, 15vw, 220px);
}
/* Stacked variant: each word on its own line */.hook--stacked.word { display: block; }
/* Episode marker */.marker {
font: var(--type-label-caps-weight) var(--type-label-caps-size)/var(--type-label-caps-leading) var(--type-label-caps-family);
letter-spacing: 0.22em;
text-transform: uppercase;
color: var(--color-ink-soft);
font-size: 18px;
}
/* Brand mark in corner — small, never dominates */.mark {
position: absolute;
bottom: var(--space-xl);
right: var(--space-xl);
font: var(--type-label-caps-weight) var(--type-label-caps-size)/var(--type-label-caps-leading) var(--type-label-caps-family);
letter-spacing: 0.18em;
text-transform: uppercase;
color: var(--color-ink-soft);
}
/* Inverted canvas variant */.canvas--inverted { background: var(--color-ink); color: var(--color-surface); }
.canvas--inverted.marker, .canvas--inverted.mark { color: var(--color-surface); opacity: 0.7; }
/* Single-accent-block variant — one colored region */.canvas--accent::before {
content: "";
position: absolute;
background: var(--color-accent);
/* Position varies by layout — e.g. left third, top quarter, diagonal */width: 30%; height: 100%;
top: 0; left: 0;
z-index: 0;
}
.canvas--accent > * { position: relative; z-index: 1; }
@page { size: 1280px720px; margin: 0; }
</style></head><body><!--
Variation choices:
layout: <picked>
type-pressure: <picked>
color: <picked>
composition: <picked>
Video title (for YouTube field, NOT on canvas): "<title>"
Thumbnail text (on canvas): "<hook>"
--><articleclass="canvas <modifier classes>"><spanclass="marker"><episodemarker, e.g. "EP.12 — TITLE"></span><h1class="hook"><hooktext — splitintowordsforstackedvariant></h1><spanclass="mark"><Brandmark></span></article></body></html>
5. Test legibility (mental check)
Imagine the canvas scaled to 240×135px (a YouTube mobile feed thumbnail). At that size:
Can you read the hook text in under 1 second?
Is the contrast strong enough to pop against a busy feed?
Does the brand mark survive (or is it OK if it disappears at small size)?
If "no" to the first two, the hook is too small or contrast too low. Bump font-size up or switch to inverted canvas.
6. Verify and report
Canvas is exactly 1280×720
Architecture archetype documented AND differs from the most recent artifact in this brand
Read ../design-anti-patterns.md and verify the artifact violates none of its rules. Pay special attention to sections 2 (type emphasis), 4 (no top-metadata-row disguised as eyebrow; vary mark placement), 5 (no EP. 01 cosplay), and 8 (no animations).
Hook text is at minimum 140px (typical: 160–280px); no more than 4 words in the hook
No face, no arrow, no red circle, no thumbnail-clickbait clichés (YouTube-specific)
Brand mark, if present, is unobtrusive (corner, eyebrow style, opacity ~0.7) — or absent entirely
YouTube thumbnail at ./design/<brand-slug>/artifacts/youtube-YYYY-MM-DD-<slug>.html.
Glassmorphism without an explicit AA-contrast scrim; floating gradient "blobs" as atmosphere.
The three-up icon-card feature grid; the "hero → 3 cards → CTA" median skeleton.
One global border-radius on every element; timid evenly-weighted low-contrast palette.
Inter / Roboto / Arial / Open Sans / Lato / Helvetica / system as the primary family (Space Grotesk = yellow flag). Use a category-matched stack from the variation roster.
Value-free CTAs ("Get Started", "Learn More", "Sign Up"); the two-CTA hero. Name the real action and its value.
Required variation (every invocation):
Make at least two intentional decisions that differ from the safe defaults (palette, layout structure, typographic voice, or spatial density) AND from the most recent artifact in this brand.
Never default to "clean / minimal / modern" — that is the absence of a direction (variation-sop Rule 1).
Sketch three distinct directions, offer them as a one-line menu, generate the best-fit by default, all three only if asked (variation-sop Rule 3).
Authenticity: prefer specific over generic everywhere — real datelines (not "today"), the brand's actual voice (not "build the future" filler), concrete CTAs over placeholders.
Rules
Hook word count is hard-capped at 4. Push back on the user if they want more. The whole skill is built around small-size legibility.
No clickbait clichés (YouTube-specific). No faces, no arrows pointing at things, no red circles, no "MIND BLOWN" energy. Type-led restraint is the brand differentiator.
Pixel exact. 1280×720, no flex.
Token-pure. Every value via var(--*) except 1px borders and the canvas pixel dimensions.
Brand mark stays small or absent. If present, max 18px font-size, corner placement.
Anti-pattern compliance. This skill defers to three shared canonical references: ../design-anti-patterns.md (the hard floor — wins every conflict), ../design-principles.md (the craft floor), and ../design-variation-sop.md (direction roster + offer-3 procedure). The anti-patterns file is the canonical anti-tell list. If you find a new tell in the output, add it there.
