nl-mcp-stdio-ollama-time-demo

An end-to-end example demonstrating how to use Model Context Protocol (MCP) over STDIO in .NET to expose server-side tools and consume them from a client, then feed tool results into a local Ollama-hosted LLM for reasoning and response generation.

This project is intentionally simple and educational: a C# MCP server exposes a GetCurrentTime tool, and a C# MCP client discovers and calls that tool, then passes the result into an Ollama chat model.

Overview

What this project shows:

• How to build an MCP server in .NET using STDIO transport
• How to expose tools using [McpServerTool] attributes
• How to build an MCP client that:
  • Launches the server as a child process
  • Discovers available tools
  • Calls a tool with structured arguments
• How to integrate MCP tool output into an Ollama chat flow
• How to correctly handle STDOUT vs STDERR to avoid protocol corruption

Prerequisites

• .NET 9.0 SDK or later
  https://dotnet.microsoft.com/download/dotnet/9.0
• Ollama installed and running locally
  https://ollama.ai/
• Required Ollama model:

  ollama pull mistral:7b
  

Installation

1. Clone the repository:

   git clone https://github.com/your-username/mcp-stdio-ollama-time-demo.git
   cd mcp-stdio-ollama-time-demo
   

2. Restore NuGet packages:

   dotnet restore
   

Project Structure

.
├── MCPClient/
│   ├── Program.cs             # MCP client entry point
│   └── OllamaHttpChatClient.cs # Minimal Ollama HTTP chat client
│
└── MCPServer/
    ├── Program.cs             # MCP server host & configuration
    └── TimeTool.cs            # MCP tool definition

MCP Server

The MCP server:

• Uses STDIO as its transport
• Exposes tools via attributes
• Writes NO logs to STDOUT

Key Points

• STDOUT is reserved exclusively for MCP protocol messages
• ALL logs must go to STDERR
• Violating this will cause random client crashes or deserialization errors

Logging Configuration (Critical)

// CRITICAL FOR MCP OVER STDIO:
// MCP uses STDOUT as a strict protocol channel.
// Any log output written to STDOUT will corrupt the MCP message stream.
builder.Logging.ClearProviders();
builder.Logging.AddConsole(options =>
{
    options.LogToStandardErrorThreshold = LogLevel.Trace;
});

Example Tool

  [McpServerToolType]
public static class TimeTool
{
    [McpServerTool, Description("Get the current time for a city")]
    public static string GetCurrentTime(string city) =>
        $"It is {DateTime.Now:HH:mm} in {city}.";
}

MCP Client

The MCP client is responsible for launching the MCP server, discovering available tools, invoking them with structured arguments, and forwarding the tool output to a local Ollama-hosted language model for reasoning and response generation.

Responsibilities

The MCP client:

• Launches the MCP server executable as a child process using STDIO
• Establishes the MCP handshake and capability negotiation
• Discovers tools exposed by the server at runtime
• Invokes MCP tools with structured, named arguments
• Extracts and processes tool responses
• Passes tool output into an Ollama chat model for final response generation

Client Entry Point

Program.cs is the main entry point for the MCP client. It performs the following steps:

1. Configures logging for diagnostics
2. Starts the MCP server using the STDIO transport
3. Creates and initializes the MCP client
4. Discovers available MCP tools
5. Calls the GetCurrentTime tool
6. Forwards the tool result to Ollama
7. Prints the final AI-generated response

Logging Setup

Logging is enabled at Trace level to assist with debugging MCP protocol behavior.

using var loggerFactory = LoggerFactory.Create(builder =>
{
    builder.AddConsole();
    builder.SetMinimumLevel(LogLevel.Trace);
});

MCP Client

The MCP client:

• Launches the MCP server executable as a child process
• Discovers tools dynamically
• Calls tools with structured arguments
• Feeds tool output into an Ollama chat model

IMPORTANT: Server Executable Path

// IMPORTANT: Update the Command path to point to the MCP server executable
// on your own machine. This path is environment-specific.
Command = @"C:\Path\To\MCPServer\bin\Debug\net9.0\MCPServer.exe";

Each developer or deployment environment must update this path.

Ollama Integration

• Ollama is used after MCP tool execution
• MCP performs the action (tool call)
• Ollama performs the reasoning / explanation
• Model used: mistral:7b

Running the Project

1. Start Ollama

Make sure Ollama is running locally:

ollama serve

Verify Ollama

Make sure Ollama is running and responding correctly:

curl http://localhost:11434/api/tags

Build the MCP Server

cd MCPServer
dotnet build

Run the MCP Client

cd MCPClient
dotnet run

Client Behavior

The client will:

• Launch the MCP server via STDIO
• Discover available MCP tools
• Call GetCurrentTime
• Pass the result into Ollama
• Print the final AI response

Example Output

MCP tools discovered: GetCurrentTime — Get the current time for a city

MCP Tool Response: It is 14:32 in Illzach, France.

AI Response: The current time in Illzach, France is 14:32 CET.

Key Technologies

• .NET 9.0 (C# Console Apps)
• Model Context Protocol (MCP)
• STDIO Transport
• Ollama (local LLM runtime)
• Mistral 7B (chat model)
• Microsoft.Extensions.Logging

Why STDIO Matters

MCP over STDIO is extremely strict:

• ✅ STDOUT → MCP protocol messages ONLY
• ✅ STDERR → logs, diagnostics, exceptions
• ❌ Any accidental Console.WriteLine breaks everything

This repository intentionally highlights correct setup to avoid subtle bugs.

License

See the LICENSE file for details.

Contributing

Contributions are welcome.

If you want to extend this example:

• Async MCP tools
• Structured JSON tool outputs
• HTTP-based MCP transport
• Streaming responses
• Tool error handling

Open an issue or submit a Pull Request.