nano-banana-pro-openrouter

name	nano-banana-pro-openrouter
description	Generate or edit images via OpenRouter with the Gemini 3 Pro Image model. Use for prompt-only image generation, image edits, and multi-image compositing; supports 1K/2K/4K output.
metadata	{"skill-author":"Marie-Lynne Block","emoji":"🍌","requires":["Python 3.10+","uv","OpenRouter API key"],"bins":["uv"],"env":["OPENROUTER_API_KEY"],"primaryEnv":"OPENROUTER_API_KEY"}

Nano Banana Pro OpenRouter

Overview

Generate or edit images with OpenRouter using the google/gemini-3-pro-image-preview model. Support prompt-only generation, single-image edits, and multi-image composition.

Run commands from this skill folder so bundled scripts and assets resolve correctly.

Prompt-only generation

uv run scripts/generate_image.py \
  --prompt "A cinematic sunset over snow-capped mountains" \
  --filename sunset.png

Edit a single image

uv run scripts/generate_image.py \
  --prompt "Replace the sky with a dramatic aurora" \
  --input-image input.jpg \
  --filename aurora.png

Compose multiple images

uv run scripts/generate_image.py \
  --prompt "Combine the subjects into a single studio portrait" \
  --input-image face1.jpg \
  --input-image face2.jpg \
  --filename composite.png

Resolution

• Use --resolution with 1K, 2K, or 4K.
• Default is 1K if not specified.

System prompt customisation

The skill reads an optional system prompt from assets/SYSTEM_TEMPLATE. This allows you to customise the image generation behaviour without modifying code.

Behaviour and constraints

• Accept up to 3 input images via repeated --input-image.
• --filename accepts relative paths (saves to current directory) or absolute paths.
• If multiple images are returned, append -1, -2, etc. to the filename.
• Print MEDIA: <path> for each saved image. Do not read images back into the response.

Troubleshooting

If the script exits non-zero, check stderr against these common blockers:

Symptom	Resolution
OPENROUTER_API_KEY is not set	Ask the user to set it. PowerShell: $env:OPENROUTER_API_KEY = "sk-or-..." / bash: export OPENROUTER_API_KEY="sk-or-..."
uv: command not found or not recognised	macOS/Linux: curl -LsSf https://astral.sh/uv/install.sh | sh. Windows: powershell -ExecutionPolicy ByPass -c "irm https://astral.sh/uv/install.ps1 | iex". Then restart the terminal.
AuthenticationError / HTTP 401	Key is invalid or has no credits. Verify at https://openrouter.ai/settings/keys.

For transient errors (HTTP 429, network timeouts), retry once after 30 seconds. Do not retry the same error more than twice — surface the issue to the user instead.