A Practical Approach with MCP and OpenAI

How the Flow Works (Short Version)

Program.cs (ASP.NET Core API – .NET 9)

using Microsoft.Extensions.AI; 
using ModelContextProtocol.Client; 
using OpenAI; 
using System.ClientModel; 
var builder = WebApplication.CreateBuilder(args); 
// Enable OpenAPI 
builder.Services.AddOpenApi(); 
// Load OpenAI API key from User Secrets 
var apiKey = builder.Configuration["OpenAI:ApiKey"]; 
var credential = new ApiKeyCredential(apiKey); 
// Create OpenAI chat client 
IChatClient chatClient = new OpenAIClient(credential) 
    .GetChatClient("gpt-4o-mini") 
    .AsIChatClient(); 
// Register as singleton 
builder.Services.AddSingleton(chatClient); 
var app = builder.Build(); 
// MCP client using stdio transport 
var mcpOptions = new StdioClientTransportOptions 
{ 
    Name = "TalkToDb MCP Server", 
    Command = "dotnet", 
    Arguments = 
    [ 
        "run", 
        "--project", 
        "../TalkToDb.MCPServer/TalkToDb.MCPServer.csproj" 
    ] 
}; 
var transport = new StdioClientTransport(mcpOptions); 
await using var mcpClient = await McpClient.CreateAsync(transport); 
if (app.Environment.IsDevelopment()) 
{ 
    app.MapOpenApi(); 
} 
app.UseHttpsRedirection(); 
// Simple test endpoint 
app.MapGet("/ask", async (IChatClient client, string query) => 
{ 
    var message = new ChatMessage(ChatRole.User, query); 
    var response = await client.GetResponseAsync(message); 
    return response.Text; 
}); 
app.Run(); 

Storing the OpenAI Secret Key (Correct Way)

{ 
  "OpenAI:ApiKey": "sk-proj-your-real-key" 
} 

One MCP Tool (Database Schema Example)

using Microsoft.Data.SqlClient; 
using ModelContextProtocol.Server; 
using System.ComponentModel; 
[McpServerToolType] 
public static class DatabaseSchemaTool 
{ 
    [McpServerTool(Name = "List-Database-Tables")] 
    [Description("Returns a list of database tables and columns")] 
    public static async Task<List<string>> ListTables( 
        IConfiguration configuration) 
    { 
        var result = new List<string>(); 
        var connectionString = 
            configuration.GetConnectionString("Default"); 
        using var connection = new SqlConnection(connectionString); 
        await connection.OpenAsync(); 
        var cmd = new SqlCommand( 
            "SELECT TABLE_NAME FROM INFORMATION_SCHEMA.TABLES WHERE TABLE_TYPE='BASE TABLE'", 
            connection); 
        using var reader = await cmd.ExecuteReaderAsync(); 
        while (await reader.ReadAsync()) 
        { 
            result.Add(reader.GetString(0)); 
        } 
        return result; 
    } 
} 

Why this is safe

Example Question → Answer Flow

Why This Design Works

Final Thoughts