nanobanana-adc

name	nanobanana-adc
description	Generate images with Google's Nano Banana Pro (Gemini 3 Pro Image) using Application Default Credentials (ADC) or a GEMINI_API_KEY. Use this when the user asks to create, generate, draw, or render an image via Google / Vertex AI / Gemini.

nanobanana-adc

Image generation CLI built on Gemini 3 Pro Image (Nano Banana Pro). Unlike other Claude Code image skills, this one works with Application Default Credentials (ADC) on Vertex AI — required in enterprise / CI / Cloud Run / Cloud Build environments where GEMINI_API_KEY is not available.

When to use

Trigger this skill when the user wants to:

• Create / generate / draw / render an image via Google or Vertex AI.
• Use Gemini 3 Pro Image (gemini-3-pro-image-preview) from a corporate GCP project that uses ADC instead of a bare API key.
• Fall back to GEMINI_API_KEY when ADC is not set up.

Quick examples

# ADC mode (default — uses gcloud / metadata server)
nanobanana-adc --prompt "a cat astronaut on mars, cinematic" --output cat.png

# 16:9 2K
nanobanana-adc --prompt "futuristic tokyo skyline" --aspect 16:9 --size 2K -o tokyo.png

# API key mode (explicit override)
nanobanana-adc --prompt "..." --api-key "$GEMINI_API_KEY" -o out.png

Options

Flag	Default	Notes
-p, --prompt	(required)	Prompt text.
-o, --output	output.png	Output file path.
-a, --aspect	1:1	1:1 / 16:9 / 9:16 / 4:3 / 3:4 / 3:2 / 2:3 / 21:9 / 9:21 / 5:4.
-s, --size	1K	1K / 2K / 4K.
-m, --model	gemini-3-pro-image-preview	Override model id.
--api-key	—	Gemini API key. Falls back to GEMINI_API_KEY then ADC when omitted.

Environment variables

Variable	Required (ADC)	Purpose
GOOGLE_CLOUD_PROJECT	✓	GCP project id.
GOOGLE_CLOUD_LOCATION	✓	Region (e.g. us-central1).
GOOGLE_GENAI_USE_VERTEXAI	✓	Must be true.
GOOGLE_APPLICATION_CREDENTIALS	optional	Path to ADC key file (else falls back to gcloud).
GEMINI_API_KEY	fallback	Used when ADC is not configured.

Authentication priority

1. --api-key flag
2. GEMINI_API_KEY env var
3. ADC (google-auth-library)

Troubleshooting

• Could not load the default credentials — run gcloud auth application-default login and ensure GOOGLE_CLOUD_PROJECT / GOOGLE_CLOUD_LOCATION / GOOGLE_GENAI_USE_VERTEXAI=true are set.
• PERMISSION_DENIED — ensure the ADC principal has roles/aiplatform.user on the project, and that Vertex AI image generation is enabled.
• No image returned / unexpected model error — confirm the model id (--model gemini-3-pro-image-preview) is available in your region, or explicitly fall back to an API key with --api-key "$GEMINI_API_KEY".