Install the belt CLI skill: npx skills add belt-sh/cli

YouTube Thumbnail Design

Create high-CTR YouTube thumbnails with AI image generation via inference.sh CLI.

Quick Start

Requires inference.sh CLI (belt). Install instructions

belt login

Generate a thumbnail

belt app run falai/flux-dev-lora --input '{

"prompt": "YouTube thumbnail style, close-up of a person with surprised excited expression looking at a glowing laptop screen, vibrant blue and orange color scheme, dramatic studio lighting, shallow depth of field, high contrast, cinematic",

"width": 1280,

"height": 720

}'

## Specifications

| Spec | Value |

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

| Dimensions | 1280 x 720 px (minimum) |

| Recommended | 1920 x 1080 px |

| Aspect ratio | 16:9 |

| Max file size | 2 MB |

| Formats | JPG, GIF, PNG |

## The 120px Test

Your thumbnail appears at roughly **120px wide** on mobile — that's how most viewers first see it.

**At 120px, viewers must be able to identify:**

1. The mood/emotion (from colors and expression)

2. The general subject (from composition)

3. The text (if any — only if large enough)

**Test:** view your thumbnail at 120px width. If it's a muddy blur, redesign.

## Safe Zones

┌─────────────────────────────────────────────┐

│ │

│ ✅ SAFE FOR TEXT AND KEY ELEMENTS │

│ │

│ │

│ │

│ │

│ ┌───┐ │

│ │ ⏱ │ │ ← Timestamp overlay

│ ┌────────┴───┘ │ (bottom-right)

│ ┌────┐ │ DURATION │

│ │ CH │ Chapter marker └──────────────│

└───┴────┴────────────────────────────────────┘

↑ Bottom-left: chapter/progress markers

**Avoid placing critical elements in:**

- Bottom-right corner (video duration timestamp)

- Bottom-left corner (chapter markers, progress bar)

- Extreme edges (cropping varies by device)

## Color Strategy

### High-Contrast Pairs That Work

| Combination | Mood | Best For |

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

| Yellow + Black | Urgency, attention | Tech, business, lists |

| Red + White | Energy, excitement | Entertainment, reactions |

| Blue + Orange | Professional contrast | Education, tutorials |

| Green + White | Growth, money | Finance, success stories |

| Purple + Yellow | Premium, creative | Design, art, creativity |

| White + Dark | Clean, minimal | Luxury, minimalist channels |

### Color Rules

- **Background** and **text/subject** should be complementary or high-contrast

- Avoid same-temperature colors touching (red on orange = mud)

- Use **3 colors maximum** per thumbnail

- Saturate more than real life — thumbnails compete with bright UI

## Text on Thumbnails

### When to Use Text

- Lists/numbers: "7 Tips", "Top 10"

- Strong opinions: "STOP Doing This"

- Results: "$10K in 30 Days"

- Comparisons: "vs" between two things

### When NOT to Use Text

- The video title already says it (redundant)

- The emotion/visual tells the story

- You can't make it large enough to read at 120px

### Text Rules

| Rule | Reason |

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

| Max 6 words | Readability at thumbnail size |

| Min 60pt equivalent | Must be legible at 120px width |

| Bold sans-serif font | Thin fonts disappear at small sizes |

| Contrast stroke/shadow | Ensures readability on any background |

| No small text | If it's not readable small, cut it |

## Face Expression Psychology

Thumbnails with faces get **higher CTR** than faceless thumbnails. Expression matters:

| Expression | CTR Impact | Best For |

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

| **Surprise/shock** | Highest | Reaction, reveal, discovery content |

| **Curiosity** | High | Tutorial, how-to, tips |

| **Excitement** | High | Unboxing, reviews, announcements |

| **Concern/worry** | Medium-high | Warning, mistake, problem content |

| **Confidence** | Medium | Expert advice, authority content |

| **Neutral** | Lowest | Avoid unless your brand is minimalist |

### Face Composition Rules

- Face should fill **30-50%** of the thumbnail

- Eyes looking **toward the text or subject** (directs viewer attention)

- Eyes looking at camera = connection. Eyes looking at object = curiosity.

- Place face on one side (usually left), text or subject on the other

Generate a face-forward thumbnail

belt app run falai/flux-dev-lora --input '{

"prompt": "close-up portrait of a man with genuinely surprised expression, mouth slightly open, raised eyebrows, looking at camera, left side of frame, vibrant teal background, dramatic rim lighting, YouTube thumbnail style, high contrast, cinematic",

"width": 1280,

"height": 720

}'

Generate a face-looking-at-subject thumbnail

belt app run bytedance/seedream-4-5 --input '{

"prompt": "person looking amazed at a glowing holographic chart showing upward growth, dramatic blue and green lighting, right side profile view, dark background, tech aesthetic, high energy",

"size": "2K"

}'

## Thumbnail Patterns by Content Type

### Tutorial / How-To

belt app run falai/flux-dev-lora --input '{

"prompt": "overhead flat lay of organized workspace with laptop showing code editor, colorful sticky notes, coffee cup, clean bright background, professional setup, tutorial style composition, warm lighting",

"width": 1280,

"height": 720

}'

### Before/After

belt app run falai/flux-dev-lora --input '{

"prompt": "split composition, left side dark and messy disorganized desk, right side bright clean organized minimalist workspace, dramatic contrast between chaos and order, clear dividing line in center, high contrast",

"width": 1280,

"height": 720

}'

### Product Review / Comparison

belt app run falai/flux-dev-lora --input '{

"prompt": "two products facing each other with dramatic lighting and sparks between them, competition battle concept, dark background with colorful rim lighting, versus comparison style, high energy, product photography",

"width": 1280,

"height": 720

}'

### Listicle / Number

belt app run falai/flux-dev-lora --input '{

"prompt": "dynamic arrangement of 7 different colorful objects floating in space against dark gradient background, each item distinct and clearly separated, energetic composition, vibrant saturated colors, studio lighting",

"width": 1280,

"height": 720

}'

## A/B Testing

Test one variable at a time:

| Variable | Test A vs B |
| --- | --- |
| Face vs No face | Same composition, with/without person |
| Expression | Surprise vs curiosity |
| Color scheme | Warm vs cool palette |
| Text vs No text | With/without text overlay |
| Background | Bright vs dark |
| Composition | Left-facing vs right-facing subject |

Generate variant A

belt app run falai/flux-dev-lora --input '{

"prompt": "..., bright yellow background, ...",

"width": 1280, "height": 720

}' --no-wait

Generate variant B (same prompt, different background)

belt app run falai/flux-dev-lora --input '{

"prompt": "..., dark navy background, ...",

"width": 1280, "height": 720

}' --no-wait

## Thumbnail Checklist

-  1280x720 minimum (1920x1080 preferred)

-  Under 2MB file size

-  Passes the 120px squint test

-  No critical elements in bottom-right (timestamp) or bottom-left (chapter)

-  Max 3 colors, high contrast

-  Text (if any) is max 6 words, bold, with contrast stroke

-  Face expression matches content energy (if applicable)

-  Doesn't duplicate the video title

-  Stands out from surrounding thumbnails (check your niche)

-  Works on both light and dark YouTube backgrounds

## Common Mistakes

| Mistake | Problem | Fix |
| --- | --- | --- |
| Too much text | Unreadable at thumbnail size | Max 6 words or no text |
| Low contrast | Disappears in the feed | Use complementary colors |
| Cluttered composition | Eye doesn't know where to look | One focal point |
| Generic stock photo feel | No personality, gets skipped | Authentic expressions, unique angles |
| Tiny details | Lost at 120px | Bold, simple shapes |
| Same style every video | Viewer fatigue | Vary within brand guidelines |
| Misleading thumbnail | Kills trust, hurts retention | Match the actual content |

## Related Skills

npx skills add inference-sh/skills@ai-image-generation

npx skills add inference-sh/skills@image-upscaling

npx skills add inference-sh/skills@prompt-engineering