Program.cs

using ConformanceServer.Prompts;
using ConformanceServer.Resources;
using ConformanceServer.Tools;
using Microsoft.Extensions.AI;
using ModelContextProtocol;
using ModelContextProtocol.Protocol;
using System.Collections.Concurrent;

var builder = WebApplication.CreateBuilder(args);

// Dictionary of session IDs to a set of resource URIs they are subscribed to
// The value is a ConcurrentDictionary used as a thread-safe HashSet
// because .NET does not have a built-in concurrent HashSet
ConcurrentDictionary<string, ConcurrentDictionary<string, byte>> subscriptions = new();

builder.Services
    .AddMcpServer()
    .WithHttpTransport()
    .WithTools<ConformanceTools>()
    .WithPrompts<ConformancePrompts>()
    .WithResources<ConformanceResources>()
    .WithSubscribeToResourcesHandler(async (ctx, ct) =>
    {
        if (ctx.Server.SessionId == null)
        {
            throw new McpException("Cannot add subscription for server with null SessionId");
        }
        if (ctx.Params?.Uri is { } uri)
        {
            subscriptions[ctx.Server.SessionId].TryAdd(uri, 0);

            await ctx.Server.SampleAsync([
                new ChatMessage(ChatRole.System, "You are a helpful test server"),
                new ChatMessage(ChatRole.User, $"Resource {uri}, context: A new subscription was started"),
            ],
            options: new ChatOptions
            {
                MaxOutputTokens = 100,
                Temperature = 0.7f,
            },
            cancellationToken: ct);
        }

        return new EmptyResult();
    })
    .WithUnsubscribeFromResourcesHandler(async (ctx, ct) =>
    {
        if (ctx.Server.SessionId == null)
        {
            throw new McpException("Cannot remove subscription for server with null SessionId");
        }
        if (ctx.Params?.Uri is { } uri)
        {
            subscriptions[ctx.Server.SessionId].TryRemove(uri, out _);
        }
        return new EmptyResult();
    })
    .WithCompleteHandler(async (ctx, ct) =>
    {
        // Basic completion support - returns empty array for conformance
        // Real implementations would provide contextual suggestions
        return new CompleteResult
        {
            Completion = new Completion
            {
                Values = [],
                HasMore = false,
                Total = 0
            }
        };
    })
    .WithSetLoggingLevelHandler(async (ctx, ct) =>
    {
        if (ctx.Params?.Level is null)
        {
            throw new McpProtocolException("Missing required argument 'level'", McpErrorCode.InvalidParams);
        }

        // The SDK updates the LoggingLevel field of the McpServer
        // Send a log notification to confirm the level was set
        await ctx.Server.SendNotificationAsync("notifications/message", new
        {
            Level = "info",
            Logger = "conformance-test-server",
            Data = $"Log level set to: {ctx.Params.Level}",
        }, cancellationToken: ct);

        return new EmptyResult();
    });

var app = builder.Build();

app.MapMcp();

app.MapGet("/health", () => TypedResults.Ok("Healthy"));

app.Run();