nano-banana-mcp

MCP server that generates images with Gemini 3 Pro Image on Vertex AI.

Requirements

• Node.js 18+
• Vertex AI API enabled in your GCP project
• A service account with permission to call Vertex AI

Setup

npm install

Create a .env file or export the variables directly:

export GOOGLE_SERVICE_ACCOUNT_JSON='{"type":"service_account","project_id":"your-project","private_key":"...","client_email":"..."}'
# or point to a JSON file
export GOOGLE_SERVICE_ACCOUNT_JSON=/absolute/path/to/service-account.json

export VERTEX_PROJECT_ID=your-project
export VERTEX_LOCATION=global
export NANO_BANANA_MODEL=gemini-3-pro-image-preview
export NANO_BANANA_GCS_BUCKET=your-reference-bucket
export NANO_BANANA_GCS_PREFIX=nano-banana/refs
export NANO_BANANA_OUTPUT_GCS_BUCKET=your-output-bucket
export NANO_BANANA_OUTPUT_GCS_PREFIX=nano-banana/outputs
export NANO_BANANA_OUTPUT_DIR=~/nano-banana-outputs
export NANO_BANANA_PROGRESS_INTERVAL_MS=20000
export NANO_BANANA_AUTO_TASK_4K=false
export NANO_BANANA_AUTO_TASK_TTL_MS=1200000

Notes:

• GOOGLE_SERVICE_ACCOUNT_JSON is required (JSON string or file path).
• VERTEX_PROJECT_ID is optional if the service account JSON includes project_id.
• The default model is gemini-3-pro-image-preview (Vertex preview). Override with another model ID if needed.
• NANO_BANANA_GCS_BUCKET is required if you want the server to upload local reference images to GCS.
• NANO_BANANA_GCS_PREFIX controls the object prefix for uploaded reference images (default: nano-banana/refs).
• NANO_BANANA_OUTPUT_GCS_BUCKET controls the GCS bucket for generated images (defaults to NANO_BANANA_GCS_BUCKET).
• NANO_BANANA_OUTPUT_GCS_PREFIX controls the object prefix for generated images (default: nano-banana/outputs).
• NANO_BANANA_OUTPUT_DIR sets the local save root (defaults to ~/nano-banana-outputs). Relative outputDir values resolve under this path.
• NANO_BANANA_PROGRESS_INTERVAL_MS controls how often progress notifications are emitted (ms) to keep long MCP calls alive. Set 0 to disable.
• NANO_BANANA_AUTO_TASK_4K runs 4K generations in task mode automatically to avoid client timeouts (set true to enable).
• NANO_BANANA_AUTO_TASK_TTL_MS controls how long auto-task results remain available (ms). Set 0 for no expiry.
• If you use GCS fileUri references, grant Storage Object Viewer to the Vertex AI service agent for the bucket.
• If you use referenceImagePaths, the MCP service account needs Storage Object Creator (or broader) on the bucket.
• For generated image uploads, the MCP service account needs Storage Object Creator (or broader) on the output bucket.
• If you see a 404 error with global, try a supported region like us-central1 or europe-west4.

Run

npm run dev

If you run via dist/ (e.g. npm start or an MCP config that points to dist/index.js), run npm run build after code changes.

Long-running calls

If your MCP client enforces the 60s default timeout, use progress notifications or task mode.

4K generations can be auto-run in task mode to avoid timeouts. Enable with NANO_BANANA_AUTO_TASK_4K=true if your client supports tasks. If your client does not support MCP tasks, auto-tasking returns a polling task ID via the normal tool response; call nano_banana_get_task to check status and retrieve the final result.

Progress (keeps a single request alive by resetting the timeout):

import { Client } from "@modelcontextprotocol/sdk/client/index.js";
import { StdioClientTransport } from "@modelcontextprotocol/sdk/client/stdio.js";
import { CallToolResultSchema } from "@modelcontextprotocol/sdk/types.js";

const client = new Client(
  { name: "example-client", version: "0.1.0" },
  { capabilities: {} }
);

await client.connect(
  new StdioClientTransport({ command: "nano-banana-mcp" })
);

const result = await client.request(
  {
    method: "tools/call",
    params: {
      name: "nano_banana_generate_image",
      arguments: {
        prompt: "A cinematic landscape at golden hour",
        aspectRatio: "16:9",
      },
    },
  },
  CallToolResultSchema,
  {
    onprogress: (progress) => {
      console.log(progress.message ?? progress.progress);
    },
    resetTimeoutOnProgress: true,
  }
);

Tasks (returns immediately, then poll/stream the result):

const stream = client.experimental.tasks.callToolStream(
  {
    name: "nano_banana_generate_image",
    arguments: {
      prompt: "A cinematic landscape at golden hour",
      aspectRatio: "16:9",
    },
  },
  CallToolResultSchema,
  {
    task: {
      ttl: 15 * 60 * 1000,
      pollInterval: 1000,
    },
  }
);

for await (const message of stream) {
  if (message.type === "taskStatus") {
    console.log(message.task.status, message.task.statusMessage ?? "");
  }
  if (message.type === "result") {
    console.log(message.result);
  }
}

Notes:

• Task state is stored in memory; tasks are lost when the server restarts.
• Task mode still benefits from progress notifications if the client subscribes.

Polling fallback (for clients without MCP task support):

const start = await client.request(
  {
    method: "tools/call",
    params: {
      name: "nano_banana_generate_image",
      arguments: {
        prompt: "A cinematic landscape at golden hour",
        imageSize: "4K",
        aspectRatio: "16:9",
      },
    },
  },
  CallToolResultSchema
);

// extract taskId from start.structuredContent or the text response
const poll = await client.request(
  {
    method: "tools/call",
    params: {
      name: "nano_banana_get_task",
      arguments: { taskId: "<taskId>" },
    },
  },
  CallToolResultSchema
);

Notes:

• Polling tasks are stored in memory and are cleared on server restart.
• Polling tasks expire after NANO_BANANA_AUTO_TASK_TTL_MS (set 0 to disable expiry).
• Completed polling responses include structuredContent with outputImageUris, outputImageUrls, and savedPaths when available.
• Wait a few seconds between nano_banana_get_task polls to avoid hammering the server.

MCP tool

Tool name: nano_banana_generate_image Tool name: nano_banana_get_task (polling fallback for auto-task 4K requests)

Example arguments:

{
  "prompt": "A cozy ramen shop on a rainy night, cinematic lighting",
  "aspectRatio": "16:9",
  "includeText": false
}

Responses include GCS URIs (and HTTP URLs) for generated images; image bytes are uploaded to GCS to avoid large MCP payloads. Generated images are also saved locally under NANO_BANANA_OUTPUT_DIR (or outputDir).

Optional fields:

• referenceImages: array of { "mimeType": "image/png", "data": "<base64>" } (legacy; prefer URIs or local paths)
• referenceImageUris: array of { "mimeType": "image/png", "fileUri": "gs://bucket/path.png" }
• referenceImagePaths: array of { "path": "/abs/path.png", "mimeType": "image/png" } (uploads to GCS)
• responseModalities: ["IMAGE"] or ["TEXT", "IMAGE"]
• candidateCount: integer 1-8
• imageSize: 1K, 2K, 4K (for models that support it)
• model, location, projectId: overrides
• gcsBucket: override the GCS bucket for uploads
• gcsUploadPrefix: override the GCS object prefix for uploads
• outputGcsBucket: override the GCS bucket for generated image uploads
• outputGcsPrefix: override the GCS object prefix for generated image uploads
• outputDir: directory to save generated images on disk (relative paths resolve under NANO_BANANA_OUTPUT_DIR)
• outputFilePrefix: filename prefix used when saving images and naming GCS objects

Example with a GCS reference image:

{
  "prompt": "Use the reference image for style, generate a new scene.",
  "referenceImageUris": [
    {
      "mimeType": "image/png",
      "fileUri": "gs://my-bucket/reference.png"
    }
  ]
}

Example uploading a local image and using it as a reference:

{
  "prompt": "Transform this into an isometric game scene.",
  "referenceImagePaths": [
    {
      "path": "/absolute/path/to/reference.jpg"
    }
  ]
}

References

• Gemini 3 Pro Image model card: https://docs.cloud.google.com/vertex-ai/generative-ai/docs/models/gemini/3-pro-image
• Gemini image generation docs (model IDs, response format): https://ai.google.dev/gemini-api/docs/image-generation