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MCP Mermaid ER Server

by dixitayush
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MCP Mermaid ER Server

An open-source Model Context Protocol (MCP) server that parses Mermaid ER diagrams, creates PostgreSQL database tables, and exposes automatic REST/GraphQL CRUD APIs.

MCP TypeScript License

Features

  • 🔍 Parse Mermaid ER Diagrams - Extract entities, attributes, and relationships

  • 🗄️ Auto-Create PostgreSQL Tables - Generate DDL and execute against your database

  • 🚀 REST API Generation - Automatic CRUD endpoints for all entities

  • 📊 GraphQL API Generation - Type-safe queries and mutations

  • 🔑 Key Detection - Identifies PK, FK, and UK constraints

  • ⚙️ Configurable - Environment variables for database and API settings

Installation

git clone https://github.com/yourusername/mcp-mermaid-er-server.git
cd mcp-mermaid-er-server
npm install
npm run build

Configuration

Create a .env file (copy from .env.example):

# Mermaid Source
MERMAID_DIAGRAM_PATH=./examples/sample-er.mmd

# Database (PostgreSQL)
DB_HOST=localhost
DB_PORT=5432
DB_NAME=mydb
DB_USER=postgres
DB_PASSWORD=password

# API Server
API_TYPE=rest       # rest, graphql, or both
API_PORT=3000
API_HOST=0.0.0.0

Claude Desktop Integration

Add to claude_desktop_config.json:

{
  "mcpServers": {
    "mermaid-er": {
      "command": "node",
      "args": ["/path/to/mcp-tools/dist/index.js"],
      "env": {
        "MERMAID_DIAGRAM_PATH": "/path/to/your/diagram.mmd",
        "DB_HOST": "localhost",
        "DB_NAME": "mydb",
        "DB_USER": "postgres",
        "DB_PASSWORD": "password"
      }
    }
  }
}

Available MCP Tools (12 Total)

Parsing Tools

Tool

Description

parse_er_diagram

Parse ER diagram, return full schema

list_entities

List all entity names

get_entity_details

Get attributes for an entity

get_relationships

Get all relationships

validate_diagram

Validate diagram syntax

Database Tools

Tool

Description

test_connection

Test PostgreSQL connection

generate_sql

Generate DDL without executing

create_schema

Create tables in database

drop_schema

Drop all tables (requires confirmation)

API Tools

Tool

Description

start_api_server

Start REST/GraphQL server

stop_api_server

Stop the API server

get_api_endpoints

List all endpoints

Workflow Example

  1. Parse your ER diagram → parse_er_diagram

  2. Review the SQL → generate_sql

  3. Create database tables → create_schema

  4. Start the API server → start_api_server

  5. Use the auto-generated endpoints!

API Endpoints

REST (when API_TYPE=rest or both)

GET    /api/{entity}       - List all records
GET    /api/{entity}/:id   - Get by ID
POST   /api/{entity}       - Create record
PUT    /api/{entity}/:id   - Update record
DELETE /api/{entity}/:id   - Delete record

GraphQL (when API_TYPE=graphql or both)

# Queries
query { customers { customer_id email } }
query { customer(id: "1") { email } }

# Mutations
mutation { createCustomer(input: { email: "test@example.com" }) { customer_id } }
mutation { updateCustomer(id: "1", input: { email: "new@example.com" }) { email } }
mutation { deleteCustomer(id: "1") { customer_id } }

Supported ER Syntax

erDiagram
    CUSTOMER {
        int customer_id PK "Primary key"
        string email UK "Unique email"
        string name
    }
    
    ORDER {
        int order_id PK
        int customer_id FK
        datetime order_date
    }
    
    CUSTOMER ||--o{ ORDER : "places"

Development

npm run dev      # Run with ts-node
npm run build    # Compile TypeScript
npm test         # Run tests

License

MIT License - see LICENSE

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