mcp-alphabanana

English | 日本語

mcp-alphabanana is a Model Context Protocol (MCP) server for generating image assets with Google Gemini. It is built for MCP-compatible clients and agent workflows that need fast image generation, transparent outputs, reference-image guidance, and flexible delivery formats.

Keywords: MCP server, Model Context Protocol, Gemini AI, image generation, FastMCP

Key capabilities:

• Ultra-fast Gemini image generation across Flash and Pro tiers
• Transparent PNG/WebP asset output for web and game pipelines
• Multi-image style guidance with local reference image files
• Flexible file, base64, or combined outputs for agent workflows

Quick Start

Run the MCP server with npx:

npx -y @tasopen/mcp-alphabanana

Or add it to your MCP configuration:

{
  "mcp": {
    "servers": {
      "alphabanana": {
        "command": "npx",
        "args": ["-y", "@tasopen/mcp-alphabanana"],
        "env": {
          "GEMINI_API_KEY": "${env:GEMINI_API_KEY}"
        }
      }
    }
  }
}

Set GEMINI_API_KEY before starting the server.

MCP Server

This repository provides an MCP server that enables AI agents to generate images using Google Gemini.

It can be used with MCP-compatible clients such as:

• Claude Desktop
• VS Code MCP
• Cursor

Built with FastMCP 3 for a simplified codebase and flexible output options.

Glama MCP Server badge:

Available Tools

generate_image

Generates images using Google Gemini with optional transparency, local reference images, grounding, and reasoning metadata.

Key parameters:

• prompt (string): description of the image to generate
• model: Flash3.1, Flash2.5, Pro3, flash, pro
• outputWidth and outputHeight: requested final image size in pixels
• output_resolution: 0.5K, 1K, 2K, 4K
• output_format: png, jpg, webp
• outputType: file, base64, combine
• outputPath: required when outputType is file or combine
• transparent: enable transparent PNG/WebP post-processing
• referenceImages: optional array of local reference image files
• grounding_type and thinking_mode: advanced Gemini 3.1 controls

Model Selection

Input Model ID	Internal Model ID	Description
Flash3.1	gemini-3.1-flash-image-preview	Ultra-fast, supports Thinking/Grounding.
Flash2.5	gemini-2.5-flash-image	Legacy Flash. High stability. Low cost.
Pro3	gemini-3.0-pro-image-preview	High-fidelity Pro model.
flash	gemini-3.1-flash-image-preview	Alias for backward compatibility.
pro	gemini-3.0-pro-image-preview	Alias for backward compatibility.

Parameters

Full parameter reference for the generate_image tool.

Parameter	Type	Default	Description
prompt	string	required	Description of the image to generate
outputFileName	string	required	Output filename (extension auto-added if missing)
outputType	enum	combine	file, base64, or combine
model	enum	Flash3.1	Model: Flash3.1, Flash2.5, Pro3, flash, pro
output_resolution	enum	auto	0.5K, 1K, 2K, 4K (0.5K/2K/4K: Flash3.1 only)
outputWidth	integer	required	Final output width in pixels
outputHeight	integer	required	Final output height in pixels
output_format	enum	png	png, jpg, webp
outputPath	string	required for file / combine	Absolute output directory path
transparent	boolean	false	Transparent background (PNG/WebP only)
transparentColor	string or null	null	Color key override for transparency extraction
colorTolerance	integer	30	Transparency color matching tolerance
fringeMode	enum	auto	auto, crisp, hd
resizeMode	enum	crop	crop, stretch, letterbox, contain
grounding_type	enum	none	none, text, image, both (Flash3.1 only)
thinking_mode	enum	minimal	minimal, high (Flash3.1 only)
include_thoughts	boolean	false	Return model reasoning fields when metadata is enabled
include_metadata	boolean	false	Include grounding and reasoning metadata in JSON output
referenceImages	array	[]	Up to 14 local reference files (Flash3.1/Pro3), 3 for Flash2.5
debug	boolean	false	Save intermediate debug artifacts

Why alphabanana?

• Zero Watermarks: API-native clean images.
• Thinking/Grounding Support: Higher prompt adherence and search-backed accuracy.
• Production Ready: Supports transparent WebP and exact aspect ratios for web and game assets.

Features

• Ultra-fast image generation (Gemini 3.1 Flash, 0.5K/1K/2K/4K)
• Advanced multi-image reasoning (up to 14 reference images)
• Thinking/Grounding support (Flash3.1 only)
• Transparent PNG/WebP output (color-key post-processing, despill)
• Multiple output formats: file, base64, or both
• Flexible resize modes: crop, stretch, letterbox, contain
• Multiple model tiers: Flash3.1, Flash2.5, Pro3, legacy aliases

Example Outputs

These sample outputs were generated with mcp-alphabanana and stored in examples.

Pixel art asset	Reference-image game scene	Photorealistic generation

Configuration

Configure the GEMINI_API_KEY in your MCP configuration (for example, mcp.json).

Examples:

• Reference an OS environment variable from mcp.json:

{
  "env": {
    "GEMINI_API_KEY": "${env:GEMINI_API_KEY}"
  }
}

• Provide the key directly in mcp.json:

{
  "env": {
    "GEMINI_API_KEY": "your_api_key_here"
  }
}

VS Code Integration

Add to your VS Code settings (.vscode/settings.json or user settings), configuring the server env in mcp.json or via the VS Code MCP settings.

{
  "mcp": {
    "servers": {
      "mcp-alphabanana": {
        "command": "npx",
        "args": ["-y", "@tasopen/mcp-alphabanana"],
        "env": {
          "GEMINI_API_KEY": "${env:GEMINI_API_KEY}"
        }
      }
    }
  }
}

Optional: Set a custom fallback directory for write failures by adding MCP_FALLBACK_OUTPUT to the env object.

Usage Examples

Basic Generation

{
  "prompt": "A pixel art treasure chest, golden trim, wooden texture",
  "model": "Flash3.1",
  "outputFileName": "chest",
  "outputType": "base64",
  "outputWidth": 64,
  "outputHeight": 64,
  "transparent": true
}

Advanced (Vertical poster and thinking)

{
  "prompt": "A vertical, photorealistic travel poster advertising Magical Wings Day Tours. A joyful young couple flies high above a breathtaking European countryside at golden hour, holding hands as they soar through a partly cloudy sky. Below them are vineyards, villages, forests, a winding river, and a hilltop medieval castle. The poster uses large, elegant typography with the headline FLY THE COUNTRYSIDE at the top and Magical Wings Day Tours branding near the bottom.",
  "model": "Flash3.1",
  "output_resolution": "1K",
  "outputFileName": "photoreal-travel-poster",
  "outputType": "file",
  "outputPath": "/path/to/output",
  "outputWidth": 848,
  "outputHeight": 1264,
  "output_format": "jpg",
  "thinking_mode": "high",
  "include_metadata": true
}

Grounding Sample (Search-backed)

{
  "prompt": "A modern travel poster featuring today's weather and skyline highlights in Kuala Lumpur",
  "model": "Flash3.1",
  "outputFileName": "kl_travel_poster",
  "outputType": "base64",
  "outputWidth": 1024,
  "outputHeight": 1024,
  "grounding_type": "text",
  "thinking_mode": "high",
  "include_metadata": true,
  "include_thoughts": true
}

This sample enables Google Search grounding and returns grounding and reasoning metadata in JSON.

With Reference Images

{
  "prompt": "Use the reference image to create a game screen showing an opened treasure chest filled with coins and treasure, 8-bit dungeon crawler style, after-battle reward scene, dungeon corridor background, four-party status UI at the bottom",
  "model": "Flash3.1",
  "output_resolution": "0.5K",
  "outputFileName": "reference-image-dungeon-loot",
  "outputType": "file",
  "outputPath": "/path/to/output",
  "outputWidth": 600,
  "outputHeight": 448,
  "output_format": "webp",
  "transparent": false,
  "referenceImages": [
    {
      "description": "Treasure chest style reference",
      "filePath": "/path/to/references/pixel-art-treasure-chest.png"
    }
  ]
}

Transparency & Output Formats

• PNG: Full alpha, color-key + despill
• WebP: Full alpha, better compression (Flash3.1+)
• JPEG: No transparency (falls back to solid background)

Development

# Development mode with MCP CLI
npm run dev

# MCP Inspector (Web UI)
npm run inspect

# Build for production
npm run build

License

MIT