Install the belt CLI skill:
npx skills add belt-sh/cli
Book Cover Design
Create genre-appropriate book covers with AI image generation via inference.sh CLI.
Quick Start
Requires inference.sh CLI (
belt). Install instructions
belt login
# Generate a thriller cover concept
belt app run falai/flux-dev-lora --input '{
"prompt": "dark moody book cover art, lone figure standing at end of a rain-soaked alley, dramatic chiaroscuro lighting, noir atmosphere, cinematic, high contrast shadows",
"width": 832,
"height": 1248
}'
Genre Conventions
Readers judge books by covers. Matching genre expectations is critical — a romance reader will skip a cover that looks like sci-fi, regardless of content.
Fiction
| Genre | Palette | Imagery | Typography | Mood |
|---|---|---|---|---|
| Thriller/Mystery | Dark (black, navy, blood red) | Lone figure, urban scenes, shadows | Bold sans-serif, all caps | Tense, ominous |
| Romance | Warm (pink, red, gold, soft purple) | Couples, flowers, scenic backdrops | Script/cursive, elegant serif | Passionate, dreamy |
| Sci-Fi | Cool (blue, teal, purple, silver) | Space, tech, geometric shapes | Clean sans-serif, futuristic | Vast, technological |
| Fantasy | Rich saturated (emerald, crimson, gold) | Swords, magic, landscapes, creatures | Decorative serif, ornamental | Epic, magical |
| Literary Fiction | Muted, sophisticated | Abstract, minimal, symbolic | Elegant serif, understated | Thoughtful, artistic |
| Horror | Dark with high contrast pops | Faces, shadows, isolation, decay | Distressed, bold, dripping | Dread, unease |
| Historical | Sepia, muted period-accurate | Period clothing, architecture, artifacts | Classical serif | Nostalgic, authentic |
Non-Fiction
| Category | Style | Imagery | Typography |
|---|---|---|---|
| Business/Self-help | Clean, bold, 2-3 colors | Minimal or none, icon optional | Large bold sans-serif title |
| Memoir | Personal, warm | Author photo or atmospheric scene | Mix of serif and sans |
| Science/Academic | Professional, structured | Diagrams, abstract visuals | Clean serif, structured layout |
| Cookbook | Appetizing, bright | Hero food photograph | Warm, inviting fonts |
| Travel | Vibrant, aspirational | Destination photography | Adventure-style fonts |
Cover Sizing
Print (Trim Sizes)
| Format | Dimensions | Common For |
|---|---|---|
| Mass market paperback | 4.25 x 6.87" | Genre fiction |
| Trade paperback | 5.5 x 8.5" | Most fiction/non-fiction |
| Standard | 6 x 9" | Non-fiction, textbooks |
| Large format | 7 x 10" | Coffee table, art books |
Digital
| Platform | Cover Size | Aspect Ratio |
|---|---|---|
| Amazon Kindle | 2560 x 1600 px (min 1000 x 625) | 1.6:1 |
| Apple Books | 1400 x 1873 px minimum | ~3:4 |
| General ebook | 2500 x 3750 px | 2:3 |
Spine Width
Approximate: page count / 400 = spine width in inches (varies by paper stock).
- 200 pages ≈ 0.5" spine
- 400 pages ≈ 1.0" spine
Layout Zones
┌─────────────────────────┐
│ TITLE ZONE │ ← Top 1/3: Title must be readable here
│ (largest text) │ This is what shows in thumbnails
│ │
│ │
│ MAIN IMAGE │ ← Middle: Core visual/illustration
│ ZONE │ The emotional hook
│ │
│ │
│ SUBTITLE / │ ← Bottom area: Author name, subtitle
│ AUTHOR ZONE │ Smaller text, less critical at thumbnail
└─────────────────────────┘
The Thumbnail Test
Your cover will be seen at 80x120px on Amazon, 60x90px in search results, and ~40x60px on mobile grids.
At thumbnail size, readers must be able to identify:
- The genre (from color and composition)
- The title (if large enough)
- The mood (from imagery)
Test: shrink your cover to 80px wide. If you can't read the title or identify the genre, redesign.
Prompting by Genre
Thriller
belt app run falai/flux-dev-lora --input '{
"prompt": "dark cinematic book cover scene, silhouette of a person standing before a foggy bridge at night, single streetlamp casting long shadows, noir atmosphere, high contrast, desaturated blue tint, dramatic tension",
"width": 832,
"height": 1248
}'
Romance
belt app run bytedance/seedream-4-5 --input '{
"prompt": "romantic soft-focus scene, couple silhouetted against golden sunset on a beach, warm pink and gold tones, bokeh lights, dreamy atmosphere, soft pastel sky, intimate mood",
"size": "2K"
}'
Sci-Fi
belt app run falai/flux-dev-lora --input '{
"prompt": "science fiction book cover art, massive space station orbiting a ringed planet, deep blue and teal color palette, stars and nebula background, hard sci-fi aesthetic, cinematic scale, clean geometric architecture",
"width": 832,
"height": 1248
}'
Fantasy
belt app run xai/grok-imagine-image-pro --input '{
"prompt": "epic fantasy book cover illustration, ancient stone castle on a cliff overlooking a misty valley, magical aurora in the sky, rich emerald and gold colors, detailed environment, sense of wonder and adventure",
"aspect_ratio": "2:3"
}'
Non-Fiction / Business
belt app run falai/flux-dev-lora --input '{
"prompt": "minimal abstract book cover background, clean gradient from deep navy to white, subtle geometric pattern, professional and modern, negative space, corporate aesthetic",
"width": 832,
"height": 1248
}'
Typography Rules
AI cannot render text reliably. Generate the cover art/background with AI, then add typography in a design tool.
Title Hierarchy
- Title — largest, most prominent, top 1/3 of cover
- Subtitle — smaller, below title or at bottom
- Author name — bottom of cover, size depends on author recognition
Font Pairing by Genre
- Thriller: bold sans-serif title + condensed sans-serif author
- Romance: script/cursive title + elegant serif author
- Sci-Fi: geometric sans-serif for both
- Fantasy: decorative/medieval serif title + clean serif author
- Business: heavy bold sans-serif title + light sans-serif subtitle
Iteration Workflow
# 1. Generate 5+ concepts across different models
belt app run falai/flux-dev-lora --input '{"prompt": "...", "width": 832, "height": 1248}' --no-wait
belt app run bytedance/seedream-4-5 --input '{"prompt": "..."}' --no-wait
belt app run xai/grok-imagine-image-pro --input '{"prompt": "...", "aspect_ratio": "2:3"}' --no-wait
# 2. Refine best concept with image-to-image editing
belt app run bytedance/seededit-3-0-i2i --input '{
"prompt": "make the sky more dramatic with storm clouds, increase contrast",
"image": "path/to/best-concept.png"
}'
# 3. Upscale for print quality
belt app run falai/topaz-image-upscaler --input '{
"image": "path/to/final-cover.png",
"scale": 4
}'
Common Mistakes
| Mistake | Problem | Fix |
|---|---|---|
| Wrong genre signals | Readers skip it | Study bestsellers in your genre |
| Title too small | Invisible at thumbnail | Title should fill top 1/3 |
| Too much detail | Muddy at small sizes | Simplify, use negative space |
| AI-generated text | Garbled letters | Add text in design tool |
| Centered everything | Static, boring | Use asymmetry intentionally |
| Following trends blindly | Dates quickly | Classic genre conventions endure |
Checklist
- Genre instantly recognizable from colors and composition
- Title readable at 80px wide (thumbnail test)
- No AI-generated text on cover
- Works in both color and greyscale
- Correct dimensions for target platform
- Author name visible but not competing with title
- High resolution (300 DPI for print, 2500px+ for digital)
- Spine text readable (for print)
Related Skills
npx skills add inference-sh/skills@ai-image-generation
npx skills add inference-sh/skills@prompt-engineering
npx skills add inference-sh/skills@image-upscaling
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