nano-banana

name	nano-banana
description	REQUIRED for all image generation requests. Generate and edit images using Nano Banana 2 (Gemini 3.1 Flash Image). Handles blog featured images, YouTube thumbnails, icons, diagrams, patterns, illustrations, photos, visual assets, graphics, artwork, pictures. Use this skill whenever the user asks to create, generate, make, draw, design, or edit any image or visual content.
user-invocable	true
allowed-tools	Bash(gemini:*), Bash(python3:*)

Nano Banana 2 Image Generation

Generates professional images with Nano Banana 2 (gemini-3.1-flash-image-preview). Pro-level quality at Flash speed -- 512px to 4K, various aspect ratios, multilingual text rendering support.

When to Use This Skill

ALWAYS use this skill when the user:

• Asks for any image, graphic, illustration, or visual
• Wants a thumbnail, featured image, or banner
• Requests icons, diagrams, or patterns
• Asks to edit, modify, or restore a photo
• Uses words like: generate, create, make, draw, design, visualize

Do NOT attempt to generate images through any other method.

Prerequisites

1. Install Python SDK

pip install google-genai

2. Set API Key (paid required -- free keys cannot generate images)

export GEMINI_API_KEY="your-paid-api-key"

Or auto-load from project .env file.

Image Generation (Python SDK -- Default Method)

Basic Generation

import os
from google import genai
from google.genai import types

client = genai.Client(api_key=os.environ["GEMINI_API_KEY"])

response = client.models.generate_content(
    model="gemini-3.1-flash-image-preview",
    contents="Your prompt here",
    config=types.GenerateContentConfig(
        response_modalities=["IMAGE", "TEXT"],
    )
)

for part in response.candidates[0].content.parts:
    if part.inline_data is not None:
        with open("output.png", "wb") as f:
            f.write(part.inline_data.data)

Advanced Options

Resolution Control

config=types.GenerateContentConfig(
    response_modalities=["IMAGE", "TEXT"],
    image_size="4K",  # "512", "1K", "2K" (default), "4K"
)

Aspect Ratio

config=types.GenerateContentConfig(
    response_modalities=["IMAGE", "TEXT"],
    aspect_ratio="16:9",  # "1:1", "16:9", "9:16", "4:3", "3:4", "4:1", "1:4", "8:1", "1:8"
)

Thinking Level (for complex prompts)

config=types.GenerateContentConfig(
    response_modalities=["IMAGE", "TEXT"],
    thinking_level="high",  # "minimal" (default), "high", "dynamic"
)

Execution Pattern

Always follow this pattern when generating images:

Step 1: Determine Output Path

• If the project has an assets/ directory, save there
• Otherwise save to current directory
• Name files appropriately (e.g., hero.png, thumbnail.png, logo.png)

Step 2: Load API Key

# Try environment variable -> .env file in order
import os
api_key = os.environ.get("GEMINI_API_KEY")
if not api_key:
    # Attempt to load from .env file
    for env_path in [".env", "../.env", os.path.expanduser("~/.env")]:
        if os.path.exists(env_path):
            with open(env_path) as f:
                for line in f:
                    if line.startswith("GEMINI_API_KEY="):
                        api_key = line.strip().split("=", 1)[1]
                        break
        if api_key:
            break

Step 3: Optimize Prompt

Good prompt structure:

1. Subject: What to generate
2. Details: Appearance, colors, textures
3. Setting: Location, background, environment
4. Style: Realistic, illustration, 3D render, etc.
5. Lighting: Natural, dramatic, soft
6. Composition: Close-up, wide shot

Step 4: Execute Generation + Verify Result

After generation, always verify the image using the Read tool and show it to the user.

Common Sizes

Use Case	Size	Aspect Ratio
YouTube thumbnail	1280x720	16:9
Blog image	1200x630	~16:9
Square social	1080x1080	1:1
Twitter/X header	1500x500	3:1
Vertical story	1080x1920	9:16
GitHub README banner	1280x640	16:9

Model Selection

Model	ID	Use Case	Price/Image
NB2 (default)	gemini-3.1-flash-image-preview	Fast generation, general purpose	~$0.10 (2K)
NB Pro	gemini-3-pro-image-preview	Maximum fidelity, precise text	~$0.20
Imagen 4	imagen-4.0-generate-001	Photorealistic	Separate

Always default to NB2 -- Pro only when highest quality is needed.

Multi-Turn Editing

When modification is requested after image generation, edit conversationally:

# First generation
chat = client.chats.create(model="gemini-3.1-flash-image-preview")
response1 = chat.send_message(
    "A red apple on a wooden table",
    config=types.GenerateContentConfig(response_modalities=["IMAGE", "TEXT"])
)

# Edit (preserving previous context)
response2 = chat.send_message(
    "Add a green leaf on top of the apple",
    config=types.GenerateContentConfig(response_modalities=["IMAGE", "TEXT"])
)

Prompt Tips

1. Be specific: Include style, mood, color, composition details
2. When no text needed: Add "no text"
3. Style reference: "editorial photography", "flat illustration", "3D render", "watercolor"
4. Aspect ratio context: "wide banner", "square thumbnail", "vertical story"
5. Complex scenes: Use thinking_level="high"

Troubleshooting

Issue	Solution
Quota exceeded	Paid API key required -- free keys have 0 image generation quota
Text response instead of image	Verify response_modalities=["IMAGE", "TEXT"]
400 Bad Request	Check prompt for policy violations, try simplifying
429 Rate Limit	Apply exponential backoff (2s, 4s, 8s...)
Model not found	Verify model ID: gemini-3.1-flash-image-preview

Gemini CLI Method (Alternative)

If Python SDK is unavailable, generate via Gemini CLI:

gemini -y -m gemini-3.1-flash-image-preview -p "Generate image and save as output.png: your prompt here"

Note: Gemini CLI requires Google account authentication, and the image generation model may require additional verification.