MCP Mssql Server

An MCP server that exposes a single execute_sql tool for running parameterless SQL statements against Microsoft SQL Server using the native msnodesqlv8 driver. It is intended for MCP-compatible clients that need direct database access over stdio without exposing credentials in logs.

Features

• SQL Server Native Driver: Uses msnodesqlv8 and ensures an explicit driver prefix on every connection string.
• Secure Logging: Masks password fields when echoing the effective connection string to stderr.
• Flexible Connection Sources: Pulls the connection string from MSSQL_CONNECTION_STRING or an override supplied with each request.
• Structured Results: Returns rowsAffected counts and all recordsets from the query for easy downstream parsing.
• Stdio Transport: Ships as an MCP stdio server so it can be dropped into any MCP client configuration.

Installation

npm install @atom8n/mcp-mssql

MCP Configuration

Add the following configuration to your MCP client:

{
  "mcp-mssql": {
    "command": "npx",
    "args": [
      "@atom8n/mcp-mssql"
    ]
  }
}

Available Tools

execute_sql

Execute a SQL statement against Microsoft SQL Server.

Parameters:

• query (required): T-SQL command text to execute.
• connectionString (optional): Overrides the MSSQL_CONNECTION_STRING environment variable for this call.

The tool automatically injects Driver={SQL Server Native Client 11.0} when the provided connection string omits a driver segment, so both DSN-style and bare connection strings work out of the box.

Usage Examples

Run a query with the default connection string

{
  "tool": "execute_sql",
  "arguments": {
    "query": "SELECT TOP (5) name FROM sys.databases ORDER BY name"
  }
}

Override the connection string per call

{
  "tool": "execute_sql",
  "arguments": {
    "query": "EXEC dbo.RefreshMaterializedView @name = 'daily_snapshot'",
    "connectionString": "Server=sql.internal;Database=Ops;Trusted_Connection=yes;"
  }
}

Response Format

Requests return JSON text via MCP content with the following shape:

{
  "rowsAffected": [123],
  "recordsets": [
    [
      { "name": "master" },
      { "name": "model" }
    ]
  ]
}

Development

Prerequisites

• Node.js 18+
• TypeScript 5.6+
• npm

Setup

# Clone the repository
git clone <repository-url>
cd mcp-mssql

# Install dependencies
npm install

# Build the project
npm run prepare

Project Structure

├── src/
│   ├── index.mts          # MCP server implementation
│   └── execute_sql.test.mts # Ad-hoc SQL runner for local verification
├── lib/
│   ├── index.mjs          # Compiled JavaScript
│   ├── index.mjs.map      # Source map
│   └── index.d.mts        # TypeScript declarations
├── package.json           # Package configuration
├── tsconfig.json          # TypeScript configuration
└── eslint.config.mjs      # ESLint configuration

Build Process

The project uses TypeScript with the following build configuration:

• Target: ES2015
• Module: CommonJS
• Output: lib/ directory
• Source Maps: Enabled
• Declarations: Generated

Scripts

• prepare: Compiles TypeScript and makes the binary executable
• inspect: Launches the MCP inspector against the compiled server
• test:sql: Runs src/execute_sql.test.mts with ts-node for manual checks

Dependencies

Runtime Dependencies

• @modelcontextprotocol/sdk: MCP server framework
• dotenv: Environment variable loader
• msnodesqlv8: Native SQL Server driver
• rimraf: File system utilities
• spawn-rx: Process spawning utilities

Development Dependencies

• @types/node: Node.js type definitions
• shx: Shell utilities for cross-platform compatibility
• ts-node: TypeScript execution
• typescript: TypeScript compiler

License

MIT License - see COPYING file for details.

Contributing

Please read CODE_OF_CONDUCT.md for our code of conduct and contribution guidelines.

Version

Current version: 1.0.0

Support

For issues and feature requests, please use the project's issue tracker.