MCP MSSQL Server

This is a Model Context Protocol (MCP) server for SQL Server interactions. It allows Large Language Models (LLMs) to execute SQL queries, run stored procedures, and explore database schemas with enhanced security and robustness.

Features

• Secure SQL Query Execution: Run SELECT queries against SQL Server databases. All queries are parsed and validated to ensure only SELECT statements are executed.

• Stored Procedure Support: Execute stored procedures with parameterized inputs.

• Schema Exploration: View database table and column definitions, with results cached for performance.

• Robust Connection Management: Utilizes a global connection pool for efficient reuse of database connections, with configurable retry logic and timeouts.

• Enhanced Security:

  • SQL query parsing and SELECT-only whitelist.

  • SQL_ALLOWED_DATABASES environment variable to whitelist accessible databases.

  • Protection against common SQL injection patterns for database context switching.

  • Blocks execution of potentially harmful system procedures or commands in direct queries.

• Configurable Caching: Database schema information is cached with a configurable Time-To-Live (TTL).

• Structured Logging: Integrated pino logger for detailed and structured application logs.

• Docker Ready: Simple deployment with Docker.

Quick Start

Using Docker (Recommended)

For complete Docker setup instructions, see the Docker README.

Configuration

The server is configured using environment variables. Create a .env file in the root directory (you can copy .env.example) to set these values.

For a detailed guide on all configuration options and how to set them up, please see CONFIG.

Using with Claude

To add this MCP server to Claude CLI:

In the Claude conversation, you can:

1. Execute SELECT queries:

   <mcp:execute_query database="YourDatabaseName"> SELECT TOP 10 * FROM YourTable </mcp:execute_query>

   (The database attribute is optional if operating on the default SQL_DATABASE or if SQL_ALLOWED_DATABASES implies a single choice.)

2. Execute stored procedures:

   <mcp:execute_StoredProcedure database="YourDatabaseName"> { "procedure": "YourSchema.YourProcedureName", "parameters": [ {"name": "Param1", "type": "NVarChar", "value": "SomeValue"}, {"name": "Param2", "type": "Int", "value": 123} ] } </mcp:execute_StoredProcedure>

3. Explore database schema:

   <mcp:schema> YourDatabaseName </mcp:schema>

   (If YourDatabaseName is omitted, it defaults to the SQL_DATABASE specified in the environment variables.)

Connection Handling

This MCP server utilizes a global, robust connection pool (mssql library's built-in pooling) managed by the DatabaseService.

• Efficiency: Connections are reused, reducing the overhead of establishing a new connection for each request.

• Resilience: Implements retry logic with exponential backoff for initial connection establishment.

• No Session State Across Calls: Unlike a session-per-user model, this server does not guarantee that subsequent MCP calls (e.g., two separate execute_query calls) from the LLM will use the exact same underlying database connection. Therefore, session-specific state like temporary tables or session variables created in one call may not be available in another. Each call should be considered atomic from a session state perspective. The USE [database] command is issued within each operation if the target database differs from the pool's default, ensuring context for that specific operation.

Development

Local Development Setup

Security Notes

• SELECT: The server strictly enforces that only SELECT queries can be run via the execute_query tool, using SQL parsing. DML (INSERT, UPDATE, DELETE) and DDL statements are blocked.

• Stored Procedure Execution: While stored procedures can perform any action their permissions allow, their execution is managed separately.

• Database Whitelisting: Use the SQL_ALLOWED_DATABASES environment variable to restrict which databases the server can interact with. For a detailed explanation of this feature and how it interacts with SQL_DATABASE, please see DATABASE_WHITELISTING.md.

• System Procedure Blocking: Direct execution of common system procedures (e.g., sp_, xp_) and commands like RECONFIGURE or WAITFOR DELAY via execute_query is blocked. Stored procedures should be used for legitimate system interactions.

• Input Validation: Database names for context switching and stored procedure names undergo format validation. SQL parsing provides an additional layer of validation for queries.

• Parameterized Inputs: Stored procedure parameters are handled by the mssql library, which typically parameterizes them to prevent SQL injection.

Troubleshooting

If you encounter issues:

1. Check container logs: docker logs mssql-mcp (if using Docker).

2. Check the server's console output for pino logs if running locally.

3. Verify all required environment variables in your .env file are correctly set, especially SQL_PASSWORD, SQL_SERVER, SQL_USER, and SQL_DATABASE.

4. Ensure the database(s) you are trying to access are listed in SQL_ALLOWED_DATABASES if you have set this variable.

5. Confirm network connectivity to your SQL Server instance from where the MCP server is running.

6. The test scripts (test-mcp.sh, test-session-persistence.sh) might need review/updates.

For detailed Docker troubleshooting, see the Docker README.