genmedia-image

name	genmedia-image
description	Generate images from a text prompt (optionally guided by reference images) using the genmedia Nanobanana MCP server's nanobanana_image_generation tool. Use when a task needs a still image produced from a description, with control over aspect ratio, resolution, and local vs GCS output, and verified by confirming the artifact was actually written.
license	Apache-2.0

genmedia Image

This skill generates images by calling the nanobanana_image_generation tool exposed by the genmedia Nanobanana MCP server. It is a single-purpose skill: one tool, one job. It supports both local workspace execution and remote / managed agent execution via GCS staging, and it always verifies that a real artifact was produced — never that the call merely returned without error.

Prerequisite: the genmedia Nanobanana MCP server must already be configured in your client (e.g. via this plugin's mcp.json / .mcp.json, or a manual MCP config). The server needs GOOGLE_CLOUD_PROJECT and Application Default Credentials (ADC) in its environment for Vertex AI calls.

Instructions

1. Resolve Output Storage Mode:

   • Local Mode (Default): Pass output_directory pointing to the target local workspace directory. The artifact is written to that local path.
   • Managed Agent / GCS Mode: When executing inside a managed agent container where the MCP server runs remotely on Cloud Run, pass gcs_bucket_uri (a GCS URI prefix such as your-bucket/outputs/) — or set the GENMEDIA_BUCKET environment variable — pointing to the mounted GCS environment bucket.
   • Do not pass both modes' destinations for the same call unless you intentionally want output in both places.

2. Formulate Imagery Parameters:

   • prompt (required): a detailed text description. Favor concrete style, subject, lighting, and composition language (e.g. "a photorealistic red panda sitting in a bamboo forest, golden hour lighting").
   • model (optional): defaults to gemini-3.1-flash-image. Leave unset unless you have a specific model requirement.
   • aspect_ratio (optional): defaults to 1:1. Supported ratios are model-dependent (common values include 1:1, 3:4, 4:3, 9:16, 16:9). Choose the ratio that matches the intended use (e.g. 16:9 for a hero banner, 9:16 for a vertical/mobile frame).
   • image_size (optional): 1K, 2K, or 4K. Defaults to 1K when unset. Supported sizes are model-dependent.
   • output_filename (optional): a client-predictable base name (e.g. hero.png). The extension is forced to the true output media type. When a single image is produced the name is used as-is; when multiple images are produced they are suffixed _1, _2, … before the extension. An existing file/object of the same name is overwritten.
   • seed (optional): a non-negative integer for best-effort reproducible generation.

3. Reference Images (optional, images):

   • To guide generation with existing media, pass images as a list of local file paths or GCS URIs (images, and — where the model supports it — videos or PDFs). Use this for edits, style transfer, character consistency, or compositing from source frames.
   • Ensure every referenced path/URI actually exists before the call; a missing reference produces a degraded or failed result.

4. Invoke the tool:

   • Call nanobanana_image_generation with the parameters assembled above.
   • Local Mode example params: { "prompt": "...", "aspect_ratio": "16:9", "output_directory": "./out", "output_filename": "hero.png" }
   • GCS Mode example params: { "prompt": "...", "aspect_ratio": "16:9", "gcs_bucket_uri": "your-bucket/outputs/", "output_filename": "hero.png" }
   • Reference-guided example params: { "prompt": "same character, new pose", "images": ["./refs/character.png"], "output_directory": "./out", "output_filename": "pose.png" }

5. Verify the Artifact By Existence (do not trust the response alone):

   • A tool call that returns without an error is not proof an image was written. In some clients and in GCS mode the server returns a resource_link content type that cannot be rendered even though the file was written — never assume inline data.
   • Local Mode: confirm the file exists and is a real, non-empty image, and inspect its type:

     file "<output_directory>/<output_filename>"   # e.g. "... PNG image data, 1024 x 1024"
     

   • GCS Mode: confirm the object exists at the destination prefix by listing it — do not parse the tool response:

     gcloud storage ls "gs://<gcs_bucket_uri prefix>"
     

     Note: if you relied on the GENMEDIA_BUCKET environment variable instead of passing gcs_bucket_uri explicitly, the server writes under a nanobanana_outputs/ subprefix — list gs://<GENMEDIA_BUCKET>/nanobanana_outputs/, not the bare bucket.
   • If no artifact is found, treat the generation as failed and surface the tool response for debugging rather than reporting success.