/generate-youtube-thumbnail

name: generate-youtube-thumbnail
description: >-
  Generate high-CTR YouTube thumbnails using Nano Banana 2 via the Arcads external API. Handles reference image upload, character likeness alignment, proven CTR-tested prompt formulas, and parallel batch generation. Use when the user asks to create a YouTube thumbnail, video thumbnail, A/B test thumbnail variations, or refers to thumbnail design with their face, brand assets, or product photos.

Generate YouTube Thumbnail

A reusable workflow for creating YouTube thumbnails via Arcads' Nano Banana 2 image endpoint with proper character likeness and proven CTR formulas.

When to use this skill

Trigger on phrases like:

• "make me a YouTube thumbnail"
• "create a thumbnail for this video"
• "I need thumbnail variations / A/B tests"
• "remake this thumbnail with my face"
• "generate 10 thumbnail concepts"
• "thumbnail with [me / my product / my brand]"

Read order

1. **This file** — workflow, decision tree, batch generation 2. **[shared/skills/generate-youtube-thumbnail/prompting/guide.md](../../shared/skills/generate-youtube-thumbnail/prompting/guide.md)** — likeness alignment, expressions cheat sheet, prompt structure (shared across all generative-AI APIs in this portfolio) 3. **[shared/skills/generate-youtube-thumbnail/prompting/formulas.md](../../shared/skills/generate-youtube-thumbnail/prompting/formulas.md)** — 5 proven thumbnail formulas with templates (shared) 4. **[scripts/generate-batch.sh](scripts/generate-batch.sh)** — Arcads-specific batch script (presigned upload + S3 PUT pipeline)

Prerequisites

• `.env` with `ARCADS_BASIC_AUTH` and `ARCADS_API_KEY`
• A `productId` (defaults to MASTER_CONTEXT.md's "My workspace" product)
• Reference images on disk (NOT pasted in chat — chat-pasted images are NOT accessible to the API):
• `face/` — 5+ photos of the subject (headshot + 3/4 angles + close-ups + expressions)
• `logos/` — brand logos as files (orange Claude Code starburst, black Arcads A, etc.)
• `products/` — clean product shots
• `examples/` — real ad screenshots, comparison material
• `style/` — example thumbnails the user wants to match aesthetically

If references are missing or the user pastes images in chat instead of saving them, **stop and ask the user to drop the actual files into a project folder** (e.g. `references/youtube thumbnail/`). Chat paste ≠ file on disk.

Workflow

1. Gather requirements (in order)

Ask the user for any missing context, but only what you actually need:

1. **Concept** — what's the video about? Single concept, A/B variations, or specific recreation of an existing thumbnail style? 2. **Subject** — who is in the thumbnail (the user themselves, an AI character, no person)? 3. **Brand assets** — which logos / products / brand colors should appear? 4. **Text** — what should the title text say? Will text be baked in, or added in post (Canva/Photoshop)? 5. **Comparison material** — for "real vs AI" thumbnails, what real ad and what AI-generated ad?

2. Verify references exist on disk

ls "references/youtube thumbnail/"

If references are missing, ask the user to drop them. **Do not proceed with text-only descriptions for brand-specific items** (logos, branded products, branded apparel) — you'll get generic AI approximations that don't match the brand. Generic descriptions are OK for backgrounds, expressions, and clothing.

3. Estimate cost and confirm

Always present cost as an **estimate** before firing:

> "Estimated cost: N variations × 24 credits = X credits. Tell me if you want to confirm exact pricing in the Arcads platform first."

4. Pick a formula

See **[shared/skills/generate-youtube-thumbnail/prompting/formulas.md](../../shared/skills/generate-youtube-thumbnail/prompting/formulas.md)** for the 5 proven formulas. Match the user's intent:

| User says... | Use formula | |---|---| | "Just me with my brand" / "branding thumbnail" | **Peace-sign / branding** | | "Real vs AI" / "compare" / "before/after" | **Real vs AI comparison** | | "Show the process" / "with the terminal" | **Terminal flow** | | "Surprised face" / "shocked reaction" | **Reaction shock** | | "Replace" / "alternative" / "swap out" | **Before/after split** |

5. Compose prompts

Follow the template in **[shared/skills/generate-youtube-thumbnail/prompting/guide.md](../../shared/skills/generate-youtube-thumbnail/prompting/guide.md)**:

YouTube thumbnail, 16:9 landscape.
[SUBJECT — likeness block + clothing + framing + "no hands" if applicable]
Expression: [specific expression from expressions cheat sheet]
[LEFT visual element + reference]
[RIGHT visual element + reference]
Across the top in massive bold yellow block letters with thick black outline reads [TITLE].
Background: [color + glow]
Style: [aesthetic notes]
Avoid: distorted face, extra fingers, hands visible, blurry logos, generic face

**Always include the CRITICAL CHARACTER LIKENESS block** when the subject is a real person. See `shared/skills/generate-youtube-thumbnail/prompting/guide.md`.

6. Generate (use the batch script)

Copy `scripts/generate-batch.sh` to a new versioned script (`scripts/generate-thumbnails-vN.sh`) and modify:

1. Update `REF_BASE` and `COMMON_REFS` array with your reference file paths 2. Replace the `PROMPTS` array entries with your composed prompts 3. Run with `bash scripts/generate-thumbnails-vN.sh > output/run.log 2>&1 &` 4. Monitor with `tail -F output/run.log | grep -E "DONE|FAILED|Asset"`

The script handles:

• Image upscaling (Lanczos to 1080px longest side, RGB JPEG conversion)
• Presigned upload + S3 PUT
• **Fresh upload per generation** (critical — re-using filePaths causes 500 errors)
• Parallel firing (10 in flight ≈ 1.5 min total)
• Retry on failure
• Asset polling and download

7. Review and present

After all generations complete, read each thumbnail with the Read tool and present:

• Brief verdict per thumbnail (likeness, readability, emotional impact)