mssql-mcp

A .NET-powered Model Context Protocol (MCP) server for Microsoft SQL Server.

Abstract

Why does this exist? Because the other MCP solutions in market for this are generally janky pieces of shit that don't work - certainly not on Windows.

This MCP server provides AI agents with robust, reliable access to Microsoft SQL Server databases through a clean, well-architected .NET application using Akka.NET for internal coordination and the official MCP C# SDK for protocol compliance.

Features

• Schema Discovery: AI agents can explore database structure without writing complex SQL
• Query Execution: Full SQL support for SELECT, INSERT, UPDATE, DELETE, and DDL operations
• Connection Validation: Automatic database connectivity validation on startup
• Error Handling: Comprehensive error handling with clear, actionable error messages
• Table Formatting: Query results formatted in readable tables for AI consumption
• Docker Support: Easy deployment with built-in .NET Docker tooling

Available Tools

Tool	Description
execute_sql	Execute any SQL query against the database
list_tables	List all tables with schema, name, type, and row count
list_schemas	List all available schemas/databases in the SQL Server instance

Configuration

Required Environment Variables

The MCP server requires a single environment variable:

• MSSQL_CONNECTION_STRING: Complete SQL Server connection string

Example Connection Strings

Windows Authentication:

MSSQL_CONNECTION_STRING="Server=localhost;Database=MyDatabase;Trusted_Connection=true;"

SQL Server Authentication:

MSSQL_CONNECTION_STRING="Server=localhost;Database=MyDatabase;User Id=myuser;Password=mypassword;"

Azure SQL Database:

MSSQL_CONNECTION_STRING="Server=myserver.database.windows.net;Database=mydatabase;User Id=myuser;Password=mypassword;Encrypt=true;"

Running the MCP Server

Option 1: Docker (Recommended)

The easiest way to run the MCP server is using Docker with .NET's built-in container support.

Build and Run with Docker

Clone the repository

# Clone the repository
git clone https://github.com/Aaronontheweb/mssql-mcp.git
cd mssql-mcp

Build the Docker image

dotnet publish --os linux --arch x64 /t:PublishContainer

You can run the container directly if you wish, but it's probably best to let the MCP server spin up the client:

# Run the container
docker run -it --rm \
  -e MSSQL_CONNECTION_STRING="Server=host.docker.internal;Database=MyDB;Trusted_Connection=true;" \
  mssql-mcp:latest

MCP Client Configuration

Cursor IDE

Add to your Cursor settings (Cursor Settings > Features > Model Context Protocol):

{
  "mcpServers": {
    "mssql": {
      "command": "docker",
      "args": [
          "run",
          "-i",
          "--rm",
          "-e",
          "MSSQL_CONNECTION_STRING",
          "mssql-mcp:latest"
      ],
      "env": {
          "MSSQL_CONNECTION_STRING": "Server=host.docker.internal,1533; Database=MyDb; User Id=myUser; Password=My(!)Password;TrustServerCertificate=true;"
      }
    }
  }
}

Claude Desktop

Add to your Claude Desktop configuration file:

• Windows: %APPDATA%\Claude\claude_desktop_config.json
• macOS: ~/Library/Application Support/Claude/claude_desktop_config.json

{
  "mcpServers": {
    "mssql": {
      "command": "docker",
      "args": [
          "run",
          "-i",
          "--rm",
          "-e",
          "MSSQL_CONNECTION_STRING",
          "mssql-mcp:latest"
      ],
      "env": {
          "MSSQL_CONNECTION_STRING": "Server=host.docker.internal,1533; Database=MyDb; User Id=myUser; Password=My(!)Password;TrustServerCertificate=true;"
      }
    }
  }
}

You might need to create that file and restart Claude Desktop for the changes to take effect.

Understanding Your Claude Desktop MCP Server Configuration

This JSON configuration is for Claude Desktop's Model Context Protocol (MCP) servers. It essentially teaches Claude how to connect to and use a custom "tool" that interacts with a Microsoft SQL Server (MSSQL) database.

Let's break down each part:

mcpServers

This is the top-level section where you define all your custom MCP servers. You can set up multiple servers here, each with its own unique name.

"mssql"

This is the unique name you've chosen for this particular SQL Server integration. Claude will use this name to refer to this database connection.

"command": "docker"

This line tells Claude Desktop to launch the MCP server using Docker. This means the actual server software runs inside an isolated container, and you'll need Docker Desktop installed and running on your Windows/mac/Linux machine for this to work. Alternatively, you can use remote Docker server using custon context.

"args": [...]

These are the arguments Claude Desktop passes to the docker command when starting the container:

• "run": This standard Docker command creates and starts a new container.
• "-i": Stands for "interactive," keeping the standard input open for communication between the MCP server and Claude Desktop.
• "--rm": This important argument tells Docker to automatically remove the container when it stops. This helps keep your Docker environment tidy.
• "-e", "MSSQL_CONNECTION_STRING": This passes an environment variable named MSSQL_CONNECTION_STRING into the Docker container.
• "mssql-mcp:latest": This specifies the Docker image to use. This image (mssql-mcp with the latest tag) contains the actual MCP server application designed to interact with SQL Server. You'll need to ensure this image is available (either built locally or pulled from a Docker registry).

"env": {...}

This section defines the environment variables that will be set when Docker executes the command.

• "MSSQL_CONNECTION_STRING": "Server=host.docker.internal,1533; Database=MyDb; User Id=myUser; Password=My(!)Password;TrustServerCertificate=true;"
  • This is the SQL Server connection string that the mssql-mcp Docker container will use to connect to your database.
  • Server=host.docker.internal,1533: host.docker.internal is a special Docker DNS name that lets the container reach your host machine's IP address. This is how the MCP server inside Docker can connect to your SQL Server instance, which is presumably running directly on your machine. 1533 is the port your SQL Server is listening on.
  • Database=MyDb: The name of the specific database you want to connect to.
  • User Id=myUser; Password=My(!)Password;: The credentials for a user (myUser) to log into your SQL Server.
  • TrustServerCertificate=true;: This tells the client to skip validating the server's SSL/TLS certificate. While convenient for development or when using self-signed certificates, be aware this reduces security by making you vulnerable to man-in-the-middle attacks in production environments.

---

In a Nutshell:

This configuration enables Claude Desktop to run a SQL Server-specific MCP server inside a Docker container. This server then uses the provided connection string to establish a connection to your SQL Server database, allowing Claude to interact with your data through this custom tool.

Local Binary Configuration

If running the built binary directly instead of Docker:

{
  "mcpServers": {
    "mssql": {
      "command": "/path/to/mssql-mcp/src/MSSQL.MCP/bin/Release/net9.0/MSSQL.MCP",
      "env": {
        "MSSQL_CONNECTION_STRING": "Server=localhost;Database=MyDB;Trusted_Connection=true;"
      }
    }
  }
}

Docker Networking Issues

Understanding the Problem

When running the MCP server as a Docker container, you'll encounter networking challenges when trying to connect to SQL Server instances running on your host machine or in other containers. Docker containers are isolated from the host network by default, making localhost connections impossible.

Solutions by Scenario

Scenario 1: SQL Server Running on Host Machine

Problem: Your SQL Server is installed directly on Windows/macOS/Linux, and you want the containerized MCP server to connect to it.

Solution: Use host.docker.internal instead of localhost in your connection string.

# ❌ This won't work - localhost refers to the container itself
docker run -it --rm \
  -e MSSQL_CONNECTION_STRING="Server=localhost;Database=MyDB;User Id=sa;Password=YourPassword123!;" \
  mssql-mcp:latest

# ✅ This works - host.docker.internal refers to the host machine
docker run -it --rm \
  -e MSSQL_CONNECTION_STRING="Server=host.docker.internal;Database=MyDB;User Id=sa;Password=YourPassword123!;" \
  mssql-mcp:latest

Updated MCP Client Configuration:

{
  "mcpServers": {
    "mssql": {
      "command": "docker",
      "args": [
        "run", "-i", "--rm",
        "-e", "MSSQL_CONNECTION_STRING=Server=host.docker.internal;Database=MyDB;User Id=sa;Password=YourPassword123!;",
        "mssql-mcp:latest"
      ]
    }
  }
}

Scenario 2: SQL Server in Another Docker Container

Solution: Use Docker Compose with a custom network and reference containers by service name.

version: '3.8'
networks:
  sql-network:
    driver: bridge

services:
  mssql-mcp:
    build: .
    environment:
      # Use the service name 'sqlserver' as the hostname
      - MSSQL_CONNECTION_STRING=Server=sqlserver;Database=MyDatabase;User Id=sa;Password=YourPassword123!;
    stdin_open: true
    tty: true
    networks:
      - sql-network
    depends_on:
      - sqlserver
      
  sqlserver:
    image: mcr.microsoft.com/mssql/server:2022-latest
    environment:
      - ACCEPT_EULA=Y
      - SA_PASSWORD=YourPassword123!
    networks:
      - sql-network
    ports:
      - "1433:1433"  # Expose to host for external tools

Scenario 3: Linux with Host Network Mode

Linux Only Solution: Use Docker's host networking mode for direct host network access.

# Linux only - shares the host's network stack
docker run -it --rm --network host \
  -e MSSQL_CONNECTION_STRING="Server=localhost;Database=MyDB;User Id=sa;Password=YourPassword123!;" \
  mssql-mcp:latest

Platform-Specific Considerations

Platform	host.docker.internal	Host Network Mode	Recommended Solution
Windows	✅ Works out of box	❌ Not supported	Use host.docker.internal
macOS	✅ Works out of box	❌ Not supported	Use host.docker.internal
Linux	⚠️ Requires --add-host	✅ Supported	Use --network host or host.docker.internal

Linux host.docker.internal setup:

docker run -it --rm \
  --add-host=host.docker.internal:host-gateway \
  -e MSSQL_CONNECTION_STRING="Server=host.docker.internal;Database=MyDB;User Id=sa;Password=YourPassword123!;" \
  mssql-mcp:latest

Testing Network Connectivity

To verify your container can reach the SQL Server:

# Test from inside a running container
docker exec -it <container_name> ping host.docker.internal

# Test SQL Server port specifically
docker run --rm -it mcr.microsoft.com/mssql-tools \
  /bin/bash -c "sqlcmd -S host.docker.internal -U sa -P 'YourPassword123!' -Q 'SELECT @@VERSION'"

Common Networking Troubleshooting

1. Connection Refused:

   • Verify SQL Server is listening on all interfaces: netstat -an | grep 1433
   • Check Windows Firewall allows Docker subnet access

2. DNS Resolution:

   • Test: docker run --rm busybox nslookup host.docker.internal
   • Ensure Docker Desktop is running (for Windows/macOS)

3. Container-to-Container:

   • Verify both containers are on the same Docker network
   • Use container service names, not localhost

4. Port Conflicts:

   • Ensure port 1433 isn't already bound by another process
   • Check with: netstat -tlnp | grep 1433

Usage Examples

Once configured, AI agents can use natural language to interact with your database:

"Show me all the tables in the database" → Uses list_tables tool

"Describe the structure of the Users table" → Uses execute_sql with an INFORMATION_SCHEMA query

"Find all users created in the last 30 days" → Uses execute_sql with appropriate SELECT query

"Create a new customer record" → Uses execute_sql with INSERT statement

Security Considerations

⚠️ Important Security Warnings

• Database Permissions: Only grant the minimum required permissions to the database user
• Connection Security: Use encrypted connections for production environments
• Access Control: This MCP server provides full SQL execution capabilities - ensure proper access controls
• Audit Logging: Consider enabling SQL Server audit logging for production use
• Network Security: Restrict network access to the database server appropriately

Recommended Database Permissions

For read-only access:

-- Create a dedicated user with minimal permissions
CREATE LOGIN mcp_readonly WITH PASSWORD = 'SecurePassword123!';
CREATE USER mcp_readonly FOR LOGIN mcp_readonly;

-- Grant only necessary permissions
GRANT SELECT ON SCHEMA::dbo TO mcp_readonly;
GRANT VIEW DEFINITION ON SCHEMA::dbo TO mcp_readonly;

For read-write access:

-- Create a dedicated user
CREATE LOGIN mcp_readwrite WITH PASSWORD = 'SecurePassword123!';
CREATE USER mcp_readwrite FOR LOGIN mcp_readwrite;

-- Grant necessary permissions
GRANT SELECT, INSERT, UPDATE, DELETE ON SCHEMA::dbo TO mcp_readwrite;
GRANT VIEW DEFINITION ON SCHEMA::dbo TO mcp_readwrite;

Troubleshooting

Connection Issues

1. Verify connection string: Test with SQL Server Management Studio or Azure Data Studio
2. Check firewall: Ensure SQL Server port (default 1433) is accessible
3. Enable TCP/IP: Ensure TCP/IP protocol is enabled in SQL Server Configuration Manager
4. Authentication mode: Verify SQL Server is configured for the appropriate authentication mode

Container Issues

1. Network connectivity: Use host.docker.internal instead of localhost when connecting from container to host
2. Environment variables: Ensure the connection string is properly escaped in Docker commands
3. Logs: Check container logs with docker logs <container_id>

License

This software is licensed under Apache 2.0 and is available "as is" - this means that if you turbo-nuke your database because you gave an AI agent sa access through this MCP server, we're not responsible.

Contributing

1. Fork the repository
2. Create a feature branch
3. Make your changes
4. Add tests if applicable
5. Submit a pull request

Architecture

• Akka.NET: Used for internal actor system coordination and database validation
• MCP C# SDK: Official Model Context Protocol implementation
• Microsoft.Data.SqlClient: High-performance SQL Server connectivity