csharp-sdk/samples/FileBasedMcpServer

File-Based MCP Server Sample

This sample demonstrates how to create a complete MCP (Model Context Protocol) server using .NET 10's file-based programs feature. Unlike traditional .NET projects that require a .csproj file, file-based programs allow you to write and run complete applications in a single .cs file.

Running the Sample

Simply run the Program.cs file directly:

./Program.cs

The server will start and listen for MCP messages on stdin/stdout (stdio transport).

Testing the Server

You can test the server by using @modelcontextprotocol/inspector, any stdio-compatible client, or sending JSON-RPC messages to stdin.

Using the Inspector

npx @modelcontextprotocol/inspector ./Program.cs

Using STDIN

Initialize the server

echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}' | ./Program.cs

List available tools

(
  echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}'
  sleep 0.5
  echo '{"jsonrpc":"2.0","id":2,"method":"tools/list","params":{}}'
  sleep 1
) | ./Program.cs 2>/dev/null | grep '^{' | jq .

Call the echo tool

(
  echo '{"jsonrpc":"2.0","id":1,"method":"initialize","params":{"protocolVersion":"2024-11-05","capabilities":{},"clientInfo":{"name":"test-client","version":"1.0"}}}'
  sleep 0.5
  echo '{"jsonrpc":"2.0","id":2,"method":"tools/call","params":{"name":"echo","arguments":{"message":"Hello, MCP!"}}}'
  sleep 1
) | ./Program.cs 2>/dev/null | grep '^{' | jq .

Reference

• File-Based Programs Tutorial
• C# Preprocessor Directives for File-Based Apps
• Model Context Protocol Specification