MssqlMcp.Dnx 1.0.5

MSSQL MCP Server

A Model Context Protocol server for SQL Server, built with the official MCP C# SDK 2.0 (ModelContextProtocol) and Microsoft.Data.SqlClient, over stdio.

Requirements

• .NET SDK 10 (for building / running from source)
• A SQL Server instance (local or remote)
• Native AOT publish (optional) needs a Visual Studio C++ workload (link.exe) — see Native AOT

Build & Run

cd MssqlMcp
dotnet build

Run from source

The server connects to SQL Server using one of the following, in priority order:

1. --conn "<connection string>" argument
2. MSSQL_CONN environment variable
3. Default: Server=localhost;Database=master;Integrated Security=True;TrustServerCertificate=True;

The connection string may be split across multiple args elements and/or wrapped in single quotes — ResolveConn re-joins them with spaces and strips both quote types, so a client can't accidentally quote it. Setting MSSQL_CONN keeps the secret out of the process command line.

# Windows Auth
dotnet run -- --conn "Server=localhost;Database=master;Integrated Security=True;TrustServerCertificate=True;"

# SQL Auth
dotnet run -- --conn "Server=localhost;Database=master;User Id=sa;Password=YourPassword;TrustServerCertificate=True;"

Note: the connection string is owned by the server and is never exposed to the LLM as a tool parameter.

Publish

Managed single-file (framework‑dependent)

cd MssqlMcp
# Publish a single executable that uses the .NET runtime installed on the machine.
# Do **not** set self‑contained; otherwise the optimizer aborts (NETSDK1102).
# This yields a small ~5 MB file.

dotnet publish -c Release -r win-x64 /p:PublishAot=false /p:PublishSingleFile=true --self-contained false -o .\bin\publish-single

Native AOT (fast startup, no runtime install)

cd MssqlMcp
# vswhere must be on PATH so the ILCompiler can find link.exe
$env:PATH = "C:\Program Files (x86)\Microsoft Visual Studio\Installer;" + $env:PATH
dotnet publish -c Release -r win-x64 -o .\bin\publish-aot

Output: MssqlMcp.exe (native) + Microsoft.Data.SqlClient.SNI.dll sidecar (cannot be embedded).

Troubleshooting

• NETSDK1102 (Optimizing assemblies for size is not supported): you combined single-file with --self-contained true (or left PublishAot=true). Use the framework-dependent command above, or switch to Native AOT.
• vswhere.exe is not recognized / link fails on AOT: add the VS Installer directory to PATH first (see the AOT command).
• Keyword not supported / index ... in the connection string: your MCP client is wrapping the value in quotes. Use args as two elements with no extra quotes (see below). A self-signed local SQL Server cert also needs TrustServerCertificate=True.

Connect

Register once in your MCP client as a stdio server. Prefer passing the connection string via the server's env so it never appears on the process command line:

{
  "mcpServers": {
    "mssql": {
      "command": "C:\\Development\\mssql-mcp\\MssqlMcp\\bin\\publish-single\\MssqlMcp.exe",
      "env": { "MSSQL_CONN": "Server=localhost;Database=master;User Id=sa;Password=123456;TrustServerCertificate=True" }
    }
  }
}

Alternatively, pass it as an arg -- but keep it to one clean array element, no surrounding quotes (a quoted or space-split value is tolerated by the server, but in the config it's a footgun).

The single-file build needs the .NET 10 runtime; the Native AOT build has no runtime dependency.

Run with dnx

You can run the published NuGet package directly with the .NET 10 dnx command. No local clone or permanent installation is required; dnx downloads the package from NuGet.org and starts the MCP server when your MCP client launches it.

The package is available at MssqlMcp.Dnx on NuGet.org.

Add this server to your MCP client configuration:

{
  "mcpServers": {
    "mssql": {
      "command": "dnx",
      "args": ["MssqlMcp.Dnx@1.0.4", "--yes"],
      "env": {
        "MSSQL_CONN": "Server=localhost;Database=master;User Id=sa;Password=YourPassword;TrustServerCertificate=True"
      }
    }
  }
}

Replace 1.0.4 with the release version you want. The MSSQL_CONN environment variable keeps database credentials out of the command line and is read by the server at startup. dnx is included with the .NET 10 SDK.

Tools

Security note

All tools execute against the connection string configured server-side at startup. The LLM can only pass query / filter parameters — it never sees database credentials.