Diagram Bridge MCP Server

A comprehensive MCP server that bridges the gap between LLMs and diagram creation through three powerful, independent tools: intelligent format selection, format-specific instruction generation, and professional diagram rendering (using kroki server). Each tool can be used standalone or combined in sequence for complete diagram workflows - from choosing the right format to generating the final image.

Supported Formats: Mermaid, PlantUML, C4 Model, D2, GraphViz, BPMN, Structurizr, Excalidraw, Vega-Lite

Quick Start

1. Prerequisites:

   • Node.js 18.0 or higher
   • Docker and Docker Compose

2. Install and build:

git clone git@github.com:tohachan/diagram-bridge-mcp.git
cd diagram-bridge-mcp
npm install && npm run build

3. Configure ports (optional):

# Copy and edit environment file to customize ports
cp .env.example .env
# Edit .env to set PORT and KROKI_PORT as needed

# Or set environment variables directly:
export PORT=4000        # MCP Server port (default: 3000)
export KROKI_PORT=9000  # Kroki service port (default: 8000)

4. Start services:

# Option 1: Interactive port configuration
./scripts/start-with-ports.sh

# Option 2: Default ports (3000 for MCP, 8000 for Kroki)
docker-compose up --build

# Option 3: Custom ports via environment variables
PORT=4000 KROKI_PORT=9000 docker-compose up --build

5. Add to Cursor (or any MCP client):

For direct local use (without Docker):

{
  "mcpServers": {
    "diagram-bridge-mcp": {
      "command": "node",
      "args": ["/path/to/diagram-bridge-mcp/dist/index.js"],
      "enabled": true
    }
  }
}

For Docker-based setup (recommended):

{
  "mcpServers": {
    "diagram-bridge-mcp": {
      "command": "docker",
      "args": [
        "exec", 
        "-i", 
        "diagram-bridge-mcp", 
        "node", 
        "dist/index.js"
      ],
      "enabled": true
    }
  }
}

Note: The MCP protocol uses STDIO communication. The HTTP endpoints (:3000/health) are only for Docker monitoring, not for MCP client connections.

5. Start using: The server provides three MCP tools ready for use!

💡 Usage Example

Here's a simple prompt to demonstrate the complete workflow:

"Choose the best diagram format for visualizing a current project architecture, then generate the diagram code and render it to an image file. Save the result as 'architecture-diagram'."

This single prompt will:

1. Analyze your request and recommend the optimal format
2. Get specific instructions for creating the diagram in that format
3. Create and render the final diagram to a PNG/SVG file

🎨 Examples Gallery

Want to see what's possible? Check out Examples Gallery

🛠️ Tools Overview

help_choose_diagram

Purpose: Intelligent format selection based on your requirements

• Analyzes your request using AI-powered heuristics
• Provides confidence-scored recommendations
• Works with format constraints when needed
• Generates structured prompts for optimal LLM decision-making

Example: "I need to show database relationships" → Recommends Mermaid ER diagram format with detailed reasoning

get_diagram_instructions

Purpose: Generate format-specific coding instructions

• Creates tailored prompts for any supported diagram format
• Includes syntax guidelines, best practices, and common pitfalls
• Provides working examples and output specifications
• Ensures LLMs generate syntactically correct diagram code

Example: For Mermaid format → Detailed Mermaid syntax guide with examples

render_diagram

Purpose: Transform diagram code into professional images

• Renders diagrams via integrated Kroki service
• Supports PNG and SVG output formats
• Includes intelligent caching for performance
• Provides file storage with absolute paths for easy access

Example: Mermaid code → High-quality PNG/SVG image file

⚙️ Configuration

Basic Setup

• Default storage: {project-root}/generated-diagrams/
• Default Kroki: Uses local Docker Kroki service
• Default ports: MCP Server (3000), Kroki (8000)

Port Configuration

The server automatically configures ports based on environment variables:

• External Port (PORT): The port exposed by Docker container (default: 3000)
• Kroki Port (KROKI_PORT): The port for Kroki service (default: 8000)
• Internal Communication: Services communicate internally using fixed container ports

# Interactive configuration (recommended)
./scripts/start-with-ports.sh

# Quick port change
PORT=4000 KROKI_PORT=9000 docker-compose up --build

# Check running services
curl http://localhost:4000/health  # Using your custom PORT

Note: When running in Docker, the server provides HTTP endpoints for health monitoring at /health and service info at /info.

For advanced configuration, see our Configuration Guide.

📚 Documentation

• Quick Start: Port Configuration - Fast port setup guide
• Installation Guide - Detailed setup instructions
• Docker Deployment - Container deployment options
• API Reference - Complete tool and resource documentation
• Configuration Guide - Environment variables and MCP client setup
• Development Guide - Contributing and development setup
• Architecture - System architecture and design patterns
• Performance & Security - Performance metrics and security features
• Troubleshooting - Common issues and solutions

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Perfect for: LLMs that need to create diagrams but don't know which format to use or how to render them professionally.

Powered by: Kroki - Universal diagram rendering service

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