Decouple Handlers and Collections (e.g. ToolsHandler and ToolsCollection) from Capabilities by promoting them to the options types.

Also, group all handlers in container classes, for server, I decided to move McpServerHandlers down to Mcp.Core and move the NotificationHandlers there too.

Also, Fix ListResourceTemplatesHandler issue.

Author: jozkee

README.md

@@ -174,54 +174,50 @@ using System.Text.Json;
 McpServerOptions options = new()
 {
     ServerInfo = new Implementation { Name = "MyServer", Version = "1.0.0" },
-    Capabilities = new ServerCapabilities
+    Handlers = new McpServerHandlers()
     {
-        Tools = new ToolsCapability
+        ListToolsHandler = (request, cancellationToken) =>
+        ValueTask.FromResult(new ListToolsResult
         {
-            ListToolsHandler = (request, cancellationToken) =>
-                ValueTask.FromResult(new ListToolsResult
+            Tools =
+            [
+                new Tool
                 {
-                    Tools =
-                    [
-                        new Tool
+                    Name = "echo",
+                    Description = "Echoes the input back to the client.",
+                    InputSchema = JsonSerializer.Deserialize<JsonElement>("""
                         {
-                            Name = "echo",
-                            Description = "Echoes the input back to the client.",
-                            InputSchema = JsonSerializer.Deserialize<JsonElement>("""
-                                {
-                                    "type": "object",
-                                    "properties": {
-                                      "message": {
-                                        "type": "string",
-                                        "description": "The input to echo back"
-                                      }
-                                    },
-                                    "required": ["message"]
-                                }
-                                """),
+                            "type": "object",
+                            "properties": {
+                              "message": {
+                                "type": "string",
+                                "description": "The input to echo back"
+                              }
+                            },
+                            "required": ["message"]
                         }
-                    ]
-                }),
-
-            CallToolHandler = (request, cancellationToken) =>
+                        """),
+                }
+            ]
+        }),
+        CallToolHandler = (request, cancellationToken) =>
+        {
+            if (request.Params?.Name == "echo")
             {
-                if (request.Params?.Name == "echo")
+                if (request.Params.Arguments?.TryGetValue("message", out var message) is not true)
                 {
-                    if (request.Params.Arguments?.TryGetValue("message", out var message) is not true)
-                    {
-                        throw new McpException("Missing required argument 'message'");
-                    }
-
-                    return ValueTask.FromResult(new CallToolResult
-                    {
-                        Content = [new TextContentBlock { Text = $"Echo: {message}", Type = "text" }]
-                    });
+                    throw new McpException("Missing required argument 'message'");
                 }
 
-                throw new McpException($"Unknown tool: '{request.Params?.Name}'");
-            },
+                return ValueTask.FromResult(new CallToolResult
+                {
+                    Content = [new TextContentBlock { Text = $"Echo: {message}", Type = "text" }]
+                });
+            }
+
+            throw new McpException($"Unknown tool: '{request.Params?.Name}'");
         }
-    },
+    }
 };
 
 await using McpServer server = McpServer.Create(new StdioServerTransport("MyServer"), options);

docs/concepts/elicitation/samples/client/Program.cs

@@ -18,12 +18,9 @@
         Name = "ElicitationClient",
         Version = "1.0.0"
     },
-    Capabilities = new()
+    Handlers = new()
     {
-        Elicitation = new()
-        {
-            ElicitationHandler = HandleElicitationAsync
-        }
+        ElicitationHandler = HandleElicitationAsync
     }
 };
 

samples/AspNetCoreMcpPerSessionTools/Program.cs

@@ -24,7 +24,7 @@
             {
                 mcpOptions.Capabilities = new();
                 mcpOptions.Capabilities.Tools = new();
-                var toolCollection = mcpOptions.Capabilities.Tools.ToolCollection = new();
+                var toolCollection = mcpOptions.ToolCollection = new();
 
                 foreach (var tool in tools)
                 {

samples/ChatWithTools/Program.cs

@@ -41,7 +41,10 @@
     }),
     clientOptions: new()
     {
-        Capabilities = new() { Sampling = new() { SamplingHandler = samplingClient.CreateSamplingHandler() } },
+        Handlers = new()
+        {
+            SamplingHandler = samplingClient.CreateSamplingHandler()
+        }
     },
     loggerFactory: loggerFactory);
 

samples/InMemoryTransport/Program.cs

@@ -10,13 +10,7 @@
     new StreamServerTransport(clientToServerPipe.Reader.AsStream(), serverToClientPipe.Writer.AsStream()),
     new McpServerOptions()
     {
-        Capabilities = new()
-        {
-            Tools = new()
-            {
-                ToolCollection = [McpServerTool.Create((string arg) => $"Echo: {arg}", new() { Name = "Echo" })]
-            }
-        }
+        ToolCollection = [McpServerTool.Create((string arg) => $"Echo: {arg}", new() { Name = "Echo" })]
     });
 _ = server.RunAsync();
 

src/ModelContextProtocol.Core/Client/McpClient.Methods.cs

@@ -631,11 +631,11 @@ internal static CreateMessageResult ToCreateMessageResult(ChatResponse chatRespo
     }
 
     /// <summary>
-    /// Creates a sampling handler for use with <see cref="SamplingCapability.SamplingHandler"/> that will
+    /// Creates a sampling handler for use with <see cref="McpClientHandlers.SamplingHandler"/> that will
     /// satisfy sampling requests using the specified <see cref="IChatClient"/>.
     /// </summary>
     /// <param name="chatClient">The <see cref="IChatClient"/> with which to satisfy sampling requests.</param>
-    /// <returns>The created handler delegate that can be assigned to <see cref="SamplingCapability.SamplingHandler"/>.</returns>
+    /// <returns>The created handler delegate that can be assigned to <see cref="McpClientHandlers.SamplingHandler"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="chatClient"/> is <see langword="null"/>.</exception>
     public static Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, ValueTask<CreateMessageResult>> CreateSamplingHandler(
         IChatClient chatClient)

src/ModelContextProtocol.Core/Client/McpClientExtensions.cs

@@ -19,11 +19,11 @@ namespace ModelContextProtocol.Client;
 public static class McpClientExtensions
 {
     /// <summary>
-    /// Creates a sampling handler for use with <see cref="SamplingCapability.SamplingHandler"/> that will
+    /// Creates a sampling handler for use with <see cref="McpClientHandlers.SamplingHandler"/> that will
     /// satisfy sampling requests using the specified <see cref="IChatClient"/>.
     /// </summary>
     /// <param name="chatClient">The <see cref="IChatClient"/> with which to satisfy sampling requests.</param>
-    /// <returns>The created handler delegate that can be assigned to <see cref="SamplingCapability.SamplingHandler"/>.</returns>
+    /// <returns>The created handler delegate that can be assigned to <see cref="McpClientHandlers.SamplingHandler"/>.</returns>
     /// <remarks>
     /// <para>
     /// This method creates a function that converts MCP message requests into chat client calls, enabling

src/ModelContextProtocol.Core/Client/McpClientHandlers.cs

@@ -0,0 +1,89 @@
+using Microsoft.Extensions.AI;
+using ModelContextProtocol.Protocol;
+
+namespace ModelContextProtocol.Client;
+
+/// <summary>
+/// Provides a container for handlers used in the creation of an MCP client.
+/// </summary>
+/// <remarks>
+/// <para>
+/// This class provides a centralized collection of delegates that implement various capabilities of the Model Context Protocol.
+/// </para>
+/// <para>
+/// Each handler in this class corresponds to a specific client endpoint in the Model Context Protocol and
+/// is responsible for processing a particular type of message. The handlers are used to customize
+/// the behavior of the MCP server by providing implementations for the various protocol operations.
+/// </para>
+/// <para>
+/// When a server sends a message to the client, the appropriate handler is invoked to process it
+/// according to the protocol specification. Which handler is selected
+/// is done based on an ordinal, case-sensitive string comparison.
+/// </para>
+/// </remarks>
+public class McpClientHandlers
+{
+
+    /// <summary>Gets or sets notification handlers to register with the client.</summary>
+    /// <remarks>
+    /// <para>
+    /// When constructed, the client will enumerate these handlers once, which may contain multiple handlers per notification method key.
+    /// The client will not re-enumerate the sequence after initialization.
+    /// </para>
+    /// <para>
+    /// Notification handlers allow the client to respond to server-sent notifications for specific methods.
+    /// Each key in the collection is a notification method name, and each value is a callback that will be invoked
+    /// when a notification with that method is received.
+    /// </para>
+    /// <para>
+    /// Handlers provided via <see cref="NotificationHandlers"/> will be registered with the client for the lifetime of the client.
+    /// For transient handlers, <see cref="IMcpEndpoint.RegisterNotificationHandler"/> may be used to register a handler that can
+    /// then be unregistered by disposing of the <see cref="IAsyncDisposable"/> returned from the method.
+    /// </para>
+    /// </remarks>
+    public IEnumerable<KeyValuePair<string, Func<JsonRpcNotification, CancellationToken, ValueTask>>>? NotificationHandlers { get; set; }
+
+    /// <summary>
+    /// Gets or sets the handler for <see cref="RequestMethods.RootsList"/> requests.
+    /// </summary>
+    /// <remarks>
+    /// This handler is invoked when a client sends a <see cref="RequestMethods.RootsList"/> request to retrieve available roots.
+    /// The handler receives request parameters and should return a <see cref="ListRootsResult"/> containing the collection of available roots.
+    /// </remarks>
+    public Func<ListRootsRequestParams?, CancellationToken, ValueTask<ListRootsResult>>? RootsHandler { get; set; }
+
+    /// <summary>
+    /// Gets or sets the handler for processing <see cref="RequestMethods.ElicitationCreate"/> requests.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This handler function is called when an MCP server requests the client to provide additional
+    /// information during interactions. The client must set this property for the elicitation capability to work.
+    /// </para>
+    /// <para>
+    /// The handler receives message parameters and a cancellation token.
+    /// It should return a <see cref="ElicitResult"/> containing the response to the elicitation request.
+    /// </para>
+    /// </remarks>
+    public Func<ElicitRequestParams?, CancellationToken, ValueTask<ElicitResult>>? ElicitationHandler { get; set; }
+
+    /// <summary>
+    /// Gets or sets the handler for processing <see cref="RequestMethods.SamplingCreateMessage"/> requests.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This handler function is called when an MCP server requests the client to generate content
+    /// using an AI model. The client must set this property for the sampling capability to work.
+    /// </para>
+    /// <para>
+    /// The handler receives message parameters, a progress reporter for updates, and a 
+    /// cancellation token. It should return a <see cref="CreateMessageResult"/> containing the 
+    /// generated content.
+    /// </para>
+    /// <para>
+    /// You can create a handler using the <see cref="McpClientExtensions.CreateSamplingHandler"/> extension
+    /// method with any implementation of <see cref="IChatClient"/>.
+    /// </para>
+    /// </remarks>
+    public Func<CreateMessageRequestParams?, IProgress<ProgressNotificationValue>, CancellationToken, ValueTask<CreateMessageResult>>? SamplingHandler { get; set; }
+}

src/ModelContextProtocol.Core/Client/McpClientImpl.cs

@@ -49,28 +49,20 @@ internal McpClientImpl(ITransport transport, string endpointName, McpClientOptio
         var notificationHandlers = new NotificationHandlers();
         var requestHandlers = new RequestHandlers();
 
-        if (options.Capabilities is { } capabilities)
-        {
-            RegisterHandlers(capabilities, notificationHandlers, requestHandlers);
-        }
+        RegisterHandlers(options.Handlers, notificationHandlers, requestHandlers);
 
         _sessionHandler = new McpSessionHandler(isServer: false, transport, endpointName, requestHandlers, notificationHandlers, _logger);
     }
 
-    private void RegisterHandlers(ClientCapabilities capabilities, NotificationHandlers notificationHandlers, RequestHandlers requestHandlers)
+    private void RegisterHandlers(McpClientHandlers handlers, NotificationHandlers notificationHandlers, RequestHandlers requestHandlers)
     {
-        if (capabilities.NotificationHandlers is { } notificationHandlersFromCapabilities)
+        if (handlers.NotificationHandlers is { } notificationHandlersFromOptions)
         {
-            notificationHandlers.RegisterRange(notificationHandlersFromCapabilities);
+            notificationHandlers.RegisterRange(notificationHandlersFromOptions);
         }
 
-        if (capabilities.Sampling is { } samplingCapability)
+        if (handlers.SamplingHandler is { } samplingHandler)
         {
-            if (samplingCapability.SamplingHandler is not { } samplingHandler)
-            {
-                throw new InvalidOperationException("Sampling capability was set but it did not provide a handler.");
-            }
-
             requestHandlers.Set(
                 RequestMethods.SamplingCreateMessage,
                 (request, _, cancellationToken) => samplingHandler(
@@ -79,34 +71,33 @@ private void RegisterHandlers(ClientCapabilities capabilities, NotificationHandl
                     cancellationToken),
                 McpJsonUtilities.JsonContext.Default.CreateMessageRequestParams,
                 McpJsonUtilities.JsonContext.Default.CreateMessageResult);
+            
+            _options.Capabilities ??= new();
+            _options.Capabilities.Sampling ??= new();
         }
 
-        if (capabilities.Roots is { } rootsCapability)
+        if (handlers.RootsHandler is { } rootsHandler)
         {
-            if (rootsCapability.RootsHandler is not { } rootsHandler)
-            {
-                throw new InvalidOperationException("Roots capability was set but it did not provide a handler.");
-            }
-
             requestHandlers.Set(
                 RequestMethods.RootsList,
                 (request, _, cancellationToken) => rootsHandler(request, cancellationToken),
                 McpJsonUtilities.JsonContext.Default.ListRootsRequestParams,
                 McpJsonUtilities.JsonContext.Default.ListRootsResult);
+
+            _options.Capabilities ??= new();
+            _options.Capabilities.Roots ??= new();
         }
 
-        if (capabilities.Elicitation is { } elicitationCapability)
+        if (handlers.ElicitationHandler is { } elicitationHandler)
         {
-            if (elicitationCapability.ElicitationHandler is not { } elicitationHandler)
-            {
-                throw new InvalidOperationException("Elicitation capability was set but it did not provide a handler.");
-            }
-
             requestHandlers.Set(
                 RequestMethods.ElicitationCreate,
                 (request, _, cancellationToken) => elicitationHandler(request, cancellationToken),
                 McpJsonUtilities.JsonContext.Default.ElicitRequestParams,
                 McpJsonUtilities.JsonContext.Default.ElicitResult);
+
+            _options.Capabilities ??= new();
+            _options.Capabilities.Elicitation ??= new();
         }
     }
 

src/ModelContextProtocol.Core/Client/McpClientOptions.cs

@@ -11,6 +11,8 @@ namespace ModelContextProtocol.Client;
 /// </remarks>
 public sealed class McpClientOptions
 {
+    private McpClientHandlers? _handlers;
+
     /// <summary>
     /// Gets or sets information about this client implementation, including its name and version.
     /// </summary>
@@ -63,4 +65,17 @@ public sealed class McpClientOptions
     /// <para>The default value is 60 seconds.</para>
     /// </remarks>
     public TimeSpan InitializationTimeout { get; set; } = TimeSpan.FromSeconds(60);
+
+    /// <summary>
+    /// Gets or sets the container of handlers used by the client for processing protocol messages.
+    /// </summary>
+    public McpClientHandlers Handlers 
+    { 
+        get => _handlers ??= new();
+        set
+        {
+            Throw.IfNull(value);
+            _handlers = value;
+        }
+    }
 }