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