Gemini Image Generation (nano-banana)

Generate images, icons, patterns, diagrams, and visual stories using the nano-banana extension for Gemini CLI.

Prerequisites

1. Gemini CLI installed and authenticated
2. API key (required — OAuth alone is not sufficient for MCP extensions):

   export GEMINI_API_KEY="your-api-key"
   # or extension-specific:
   export NANOBANANA_GEMINI_API_KEY="your-api-key"
   

3. nano-banana extension installed:

   gemini extensions install https://github.com/gemini-cli-extensions/nanobanana
   

4. Restart Gemini CLI after installation to activate commands

Model Selection

Always use the pro model by default. Only fallback to flash if it errors or the user explicitly requests speed.

Model	Role	Quality
gemini-3-pro-image-preview	Default — all image generation	Highest quality
gemini-2.5-flash-image	Fallback — on error or if user requests speed	Good quality, faster

When invoking gemini for image tasks, always prepend the model env var to ensure the pro model is used:

# Default: pro model (always use this unless it fails)
NANOBANANA_MODEL=gemini-3-pro-image-preview gemini --yolo -p '/generate "your prompt"'

# Fallback: flash model (only on error or explicit user request)
NANOBANANA_MODEL=gemini-2.5-flash-image gemini --yolo -p '/generate "your prompt"'

If NANOBANANA_MODEL is already set in the environment, respect the user's choice. Only override if unset.

Error handling: If the pro model returns a quota/capacity/availability error, automatically retry with the flash model and inform the user which model produced the output.

Headless Mode Permissions

nano-banana tools require explicit permission in headless mode. Use --yolo to auto-approve image generation tool calls:

NANOBANANA_MODEL=gemini-3-pro-image-preview gemini --yolo -p '/generate "your prompt here"'

Note: --yolo is ONLY permitted for image generation via nano-banana. Never use --yolo for code reviews or text analysis — use --sandbox instead. Gemini's role outside of image creation is strictly advisory.

Commands Reference

All nano-banana commands run inside a Gemini CLI session. From Claude Code, invoke them via headless mode or instruct the user to run them interactively.

Important: When executing any command below from Claude Code, always prepend the model and permissions:

NANOBANANA_MODEL=gemini-3-pro-image-preview gemini --yolo -p '<command>'

The examples below show the command portion only for brevity.

/generate - Create Images

Create single or multiple images from text prompts.

# Basic generation
gemini -p '/generate "watercolor painting of a fox in a snowy forest"'

# Multiple variations
gemini -p '/generate "mountain landscape" --count=4'

# With artistic styles
gemini -p '/generate "city skyline" --styles="watercolor,oil-painting,sketch,photorealistic"'

# With variation types
gemini -p '/generate "portrait" --variations="lighting,angle,mood"'

# Grid output
gemini -p '/generate "abstract art" --count=4 --format=grid'

# Reproducible with seed
gemini -p '/generate "robot mascot" --seed=42 --count=3'

Style options: watercolor, oil-painting, sketch, photorealistic, anime, pixel-art, vintage, modern, abstract, minimalist

Variation types: lighting, angle, color-palette, composition, mood, season, time-of-day

/icon - Generate App Icons & UI Elements

Create icons optimized for specific use cases with proper sizing.

# App icon set
gemini -p '/icon "coffee cup logo" --sizes="64,128,256,512" --type="app-icon"'

# Favicon
gemini -p '/icon "letter M monogram" --sizes="16,32,64" --type="favicon"'

# UI elements
gemini -p '/icon "settings gear" --sizes="24,48" --type="ui-element" --style="minimal"'

# With rounded corners (app store style)
gemini -p '/icon "music note" --sizes="128,256,512,1024" --type="app-icon" --corners="round"'

# Transparent background
gemini -p '/icon "chat bubble" --sizes="64,128" --background="transparent"'

Icon types: app-icon, favicon, ui-element

Icon styles: flat, skeuomorphic, minimal, modern

Available sizes: 16, 32, 64, 128, 256, 512, 1024

/pattern - Seamless Patterns & Textures

Create tileable patterns for backgrounds and textures.

# Geometric pattern
gemini -p '/pattern "geometric triangles" --type="seamless" --style="geometric"'

# Organic texture
gemini -p '/pattern "marble texture" --type="texture" --style="organic" --size="512x512"'

# Wallpaper
gemini -p '/pattern "forest landscape" --type="wallpaper" --colors="duotone"'

# Dense tech pattern
gemini -p '/pattern "circuit board" --style="tech" --density="dense"'

Pattern types: seamless, texture, wallpaper

Pattern styles: geometric, organic, abstract, floral, tech

Density: sparse, medium, dense

Color schemes: mono, duotone, colorful

Sizes: 128x128, 256x256, 512x512

/story - Sequential Visual Narratives

Generate series of images that tell a story or show a process.

# Process documentation
gemini -p '/story "seed growing into a tree" --steps=4 --type="process"'

# Tutorial steps
gemini -p '/story "making pour-over coffee" --steps=6 --type="tutorial"'

# Timeline
gemini -p '/story "evolution of web design 1995-2025" --steps=5 --type="timeline"'

# Comic layout
gemini -p '/story "a day in the life of a developer" --steps=4 --layout="comic"'

Story types: story, process, tutorial, timeline

Layouts: separate, grid, comic

Transitions: smooth, dramatic, fade

/diagram - Technical Diagrams

Create technical visualizations and architectural diagrams.

# System architecture
gemini -p '/diagram "microservices e-commerce architecture" --type="architecture" --style="technical"'

# Flowchart
gemini -p '/diagram "user authentication flow" --type="flowchart" --layout="vertical"'

# Database schema
gemini -p '/diagram "social media database schema" --type="database" --complexity="detailed"'

# Network topology
gemini -p '/diagram "corporate network with DMZ" --type="network"'

# Wireframe
gemini -p '/diagram "mobile app settings page" --type="wireframe" --style="clean"'

# Mind map
gemini -p '/diagram "machine learning concepts" --type="mindmap" --complexity="comprehensive"'

Diagram types: flowchart, architecture, network, database, wireframe, mindmap, sequence

Diagram styles: professional, clean, hand-drawn, technical

Layouts: horizontal, vertical, hierarchical, circular

Complexity: simple, detailed, comprehensive

/edit - Modify Existing Images

Edit images using natural language instructions.

# Edit an existing image
gemini -p '/edit "path/to/image.png" "change the sky to sunset colors"'

# Style transfer
gemini -p '/edit "photo.jpg" "convert to watercolor painting style"'

/restore - Enhance & Repair Photos

Restore old or damaged photos.

gemini -p '/restore "old-family-photo.jpg"'

/nanobanana - Natural Language Interface

Flexible natural language interface when specific commands don't fit.

gemini -p '/nanobanana "create a set of social media banners for a tech startup, 1200x630px"'

Integration Patterns with Claude Code

Generate Icons for a Project

# 1. Generate icon set
gemini -p '/icon "your app concept" --sizes="16,32,64,128,256,512,1024" --type="app-icon" --style="modern"'

# 2. Copy to project
cp ~/generated-icons/* public/icons/

Create Diagrams for Documentation

# 1. Generate architecture diagram
gemini -p '/diagram "your system architecture" --type="architecture" --style="professional" --complexity="detailed"'

# 2. Move to docs
cp ~/generated-diagrams/* docs/images/

Create Visual Assets for README

# Generate a hero image
gemini -p '/generate "developer workspace with code and coffee, tech illustration style" --styles="modern,minimalist"'

# Generate process diagrams
gemini -p '/story "how our CI/CD pipeline works" --steps=4 --type="process" --style="consistent"'

File Management

nano-banana automatically:

• Generates descriptive filenames from prompts
• Prevents duplicate filenames
• Organizes output by command type

Generated files typically appear in:

• Current working directory, or
• ~/gemini-output/ (configurable)

Tips

• Be descriptive: More detailed prompts produce better results
• Use --preview: Add --preview to auto-open generated images
• Iterate: Use /edit to refine generated images
• Batch sizes: /icon with multiple --sizes is more efficient than separate calls
• Consistent style: For sets, use --seed to maintain visual consistency
• Pro model: Set NANOBANANA_MODEL=gemini-3-pro-image-preview for highest quality output