Add 3-arg RequestContext constructor and obsolete 2-arg to eliminate null-forgiving operator usage

docs/concepts/filters.md

@@ -317,7 +317,7 @@ Execution flow: `filter1 -> filter2 -> filter3 -> baseHandler -> filter3 -> filt
     {
         var logger = context.Services?.GetService<ILogger<Program>>();
 
-        logger?.LogInformation($"Processing request from {context.Params?.ProgressToken}");
+        logger?.LogInformation($"Processing request from {context.Params.ProgressToken}");
         var result = await next(context, cancellationToken);
         logger?.LogInformation($"Returning {result.Tools?.Count ?? 0} tools");
         return result;
@@ -339,7 +339,7 @@ Execution flow: `filter1 -> filter2 -> filter3 -> baseHandler -> filter3 -> filt
         catch (Exception ex)
         {
             var logger = context.Services?.GetService<ILogger<Program>>();
-            logger?.LogError(ex, "Error while processing CallTool request for {ProgressToken}", context.Params?.ProgressToken);
+            logger?.LogError(ex, "Error while processing CallTool request for {ProgressToken}", context.Params.ProgressToken);
 
             return new CallToolResult
             {

docs/concepts/logging/samples/server/Tools/LoggingTools.cs

@@ -13,7 +13,7 @@ public static async Task<string> LoggingTool(
         int duration = 10,
         int steps = 10)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
         var stepDuration = duration / steps;
 
         // <snippet_LoggingConfiguration >

docs/concepts/pagination/pagination.md

@@ -77,7 +77,7 @@ builder.Services.AddMcpServer()
         int startIndex = 0;
 
         // Parse cursor to determine starting position
-        if (ctx.Params?.Cursor is { } cursor)
+        if (ctx.Params.Cursor is { } cursor)
         {
             startIndex = int.Parse(cursor);
         }

docs/concepts/progress/samples/server/Tools/LongRunningTools.cs

@@ -15,7 +15,7 @@ public static async Task<string> LongRunningTool(
         int duration = 10,
         int steps = 5)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
         var stepDuration = duration / steps;
 
         for (int i = 1; i <= steps; i++)

docs/concepts/resources/resources.md

@@ -212,7 +212,7 @@ builder.Services.AddMcpServer()
     .WithResources<MyResources>()
     .WithSubscribeToResourcesHandler(async (ctx, ct) =>
     {
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             // Track the subscription (e.g., in a concurrent dictionary)
             subscriptions[ctx.Server.SessionId].TryAdd(uri, 0);
@@ -221,7 +221,7 @@ builder.Services.AddMcpServer()
     })
     .WithUnsubscribeFromResourcesHandler(async (ctx, ct) =>
     {
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             subscriptions[ctx.Server.SessionId].TryRemove(uri, out _);
         }

docs/list-of-diagnostics.md

@@ -36,3 +36,4 @@ When APIs are marked as obsolete, a diagnostic is emitted to warn users that the
 | :------------ | :----- | :---------- |
 | `MCP9001` | In place | The `EnumSchema` and `LegacyTitledEnumSchema` APIs are deprecated as of specification version 2025-11-25. Use the current schema APIs instead. |
 | `MCP9002` | Removed | The `AddXxxFilter` extension methods on `IMcpServerBuilder` (e.g., `AddListToolsFilter`, `AddCallToolFilter`, `AddIncomingMessageFilter`) were superseded by `WithRequestFilters()` and `WithMessageFilters()`. |
+| `MCP9003` | In place | The `RequestContext<TParams>(McpServer, JsonRpcRequest)` constructor is obsolete. Use the overload that accepts a `parameters` argument: `RequestContext<TParams>(McpServer, JsonRpcRequest, TParams)`. |

samples/EverythingServer/Program.cs

@@ -130,7 +130,7 @@
         {
             throw new McpException("Cannot add subscription for server with null SessionId");
         }
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             subscriptions[ctx.Server.SessionId].TryAdd(uri, 0);
 
@@ -154,7 +154,7 @@ await ctx.Server.SampleAsync([
         {
             throw new McpException("Cannot remove subscription for server with null SessionId");
         }
-        if (ctx.Params?.Uri is { } uri)
+        if (ctx.Params.Uri is { } uri)
         {
             subscriptions[ctx.Server.SessionId].TryRemove(uri, out _);
         }
@@ -212,11 +212,6 @@ await ctx.Server.SampleAsync([
     })
     .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 IMcpServer
 
         await ctx.Server.SendNotificationAsync("notifications/message", new

samples/EverythingServer/Resources/SimpleResourceType.cs

@@ -19,7 +19,7 @@ public static ResourceContents TemplateResource(RequestContext<ReadResourceReque
         int index = id - 1;
         if ((uint)index >= ResourceGenerator.Resources.Count)
         {
-            throw new NotSupportedException($"Unknown resource: {requestContext.Params?.Uri}");
+            throw new NotSupportedException($"Unknown resource: {requestContext.Params.Uri}");
         }
 
         var resource = ResourceGenerator.Resources[index];

samples/EverythingServer/Tools/LongRunningTool.cs

@@ -15,7 +15,7 @@ public static async Task<string> LongRunningOperation(
         int duration = 10,
         int steps = 5)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
         var stepDuration = duration / steps;
 
         for (int i = 1; i <= steps + 1; i++)

src/Common/Obsoletions.cs

@@ -25,4 +25,8 @@ internal static class Obsoletions
 
     // MCP9002 was used for the AddXxxFilter extension methods on IMcpServerBuilder that were superseded by
     // WithMessageFilters() and WithRequestFilters(). The APIs were removed; do not reuse this diagnostic ID.
+
+    public const string RequestContextParamsConstructor_DiagnosticId = "MCP9003";
+    public const string RequestContextParamsConstructor_Message = "Use the constructor overload that accepts a parameters argument.";
+    public const string RequestContextParamsConstructor_Url = "https://github.com/modelcontextprotocol/csharp-sdk/blob/main/docs/list-of-diagnostics.md#mcp9003";
 }

src/ModelContextProtocol.Core/RequestHandlers.cs

@@ -29,7 +29,7 @@ internal sealed class RequestHandlers : Dictionary<string, Func<JsonRpcRequest,
     /// </remarks>
     public void Set<TParams, TResult>(
         string method,
-        Func<TParams?, JsonRpcRequest, CancellationToken, ValueTask<TResult>> handler,
+        Func<TParams, JsonRpcRequest, CancellationToken, ValueTask<TResult>> handler,
         JsonTypeInfo<TParams> requestTypeInfo,
         JsonTypeInfo<TResult> responseTypeInfo)
     {
@@ -40,7 +40,7 @@ public void Set<TParams, TResult>(
 
         this[method] = async (request, cancellationToken) =>
         {
-            TParams? typedRequest = JsonSerializer.Deserialize(request.Params, requestTypeInfo);
+            TParams typedRequest = JsonSerializer.Deserialize(request.Params, requestTypeInfo)!;
             object? result = await handler(typedRequest, request, cancellationToken).ConfigureAwait(false);
             return JsonSerializer.SerializeToNode(result, responseTypeInfo);
         };

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerResource.cs

@@ -386,22 +386,22 @@ public override async ValueTask<ReadResourceResult> ReadAsync(
 
             TextContent tc => new()
             {
-                Contents = [new TextResourceContents { Uri = request.Params!.Uri, MimeType = ProtocolResourceTemplate.MimeType, Text = tc.Text }],
+                Contents = [new TextResourceContents { Uri = request.Params.Uri, MimeType = ProtocolResourceTemplate.MimeType, Text = tc.Text }],
             },
 
             DataContent dc => new()
             {
                 Contents = [new BlobResourceContents 
                 { 
-                    Uri = request.Params!.Uri, 
+                    Uri = request.Params.Uri, 
                     MimeType = dc.MediaType, 
                     Blob = EncodingUtilities.GetUtf8Bytes(dc.Base64Data.Span)
                 }],
             },
 
             string text => new()
             {
-                Contents = [new TextResourceContents { Uri = request.Params!.Uri, MimeType = ProtocolResourceTemplate.MimeType, Text = text }],
+                Contents = [new TextResourceContents { Uri = request.Params.Uri, MimeType = ProtocolResourceTemplate.MimeType, Text = text }],
             },
 
             IEnumerable<ResourceContents> contents => new()
@@ -416,14 +416,14 @@ public override async ValueTask<ReadResourceResult> ReadAsync(
                     {
                         TextContent tc => new TextResourceContents
                         {
-                            Uri = request.Params!.Uri,
+                            Uri = request.Params.Uri,
                             MimeType = ProtocolResourceTemplate.MimeType,
                             Text = tc.Text
                         },
 
                         DataContent dc => new BlobResourceContents
                         {
-                            Uri = request.Params!.Uri,
+                            Uri = request.Params.Uri,
                             MimeType = dc.MediaType,
                             Blob = EncodingUtilities.GetUtf8Bytes(dc.Base64Data.Span)
                         },
@@ -436,7 +436,7 @@ public override async ValueTask<ReadResourceResult> ReadAsync(
             {
                 Contents = strings.Select<string, ResourceContents>(text => new TextResourceContents
                 {
-                    Uri = request.Params!.Uri,
+                    Uri = request.Params.Uri,
                     MimeType = ProtocolResourceTemplate.MimeType,
                     Text = text
                 }).ToList(),

src/ModelContextProtocol.Core/Server/McpServerImpl.cs

@@ -954,7 +954,7 @@ private void ConfigureLogging(McpServerOptions options)
                 // If a handler was provided, now delegate to it.
                 if (setLoggingLevelHandler is not null)
                 {
-                    return InvokeHandlerAsync(setLoggingLevelHandler, request, jsonRpcRequest, cancellationToken);
+                    return InvokeHandlerAsync(setLoggingLevelHandler, request!, jsonRpcRequest, cancellationToken);
                 }
 
                 // Otherwise, consider it handled.
@@ -966,28 +966,27 @@ private void ConfigureLogging(McpServerOptions options)
 
     private ValueTask<TResult> InvokeHandlerAsync<TParams, TResult>(
         McpRequestHandler<TParams, TResult> handler,
-        TParams? args,
+        TParams args,
         JsonRpcRequest jsonRpcRequest,
         CancellationToken cancellationToken = default)
     {
         return _servicesScopePerRequest ?
             InvokeScopedAsync(handler, args, jsonRpcRequest, cancellationToken) :
-            handler(new(new DestinationBoundMcpServer(this, jsonRpcRequest.Context?.RelatedTransport), jsonRpcRequest) { Params = args }, cancellationToken);
+            handler(new(new DestinationBoundMcpServer(this, jsonRpcRequest.Context?.RelatedTransport), jsonRpcRequest, args), cancellationToken);
 
         async ValueTask<TResult> InvokeScopedAsync(
             McpRequestHandler<TParams, TResult> handler,
-            TParams? args,
+            TParams args,
             JsonRpcRequest jsonRpcRequest,
             CancellationToken cancellationToken)
         {
             var scope = Services?.GetService<IServiceScopeFactory>()?.CreateAsyncScope();
             try
             {
                 return await handler(
-                    new RequestContext<TParams>(new DestinationBoundMcpServer(this, jsonRpcRequest.Context?.RelatedTransport), jsonRpcRequest)
+                    new RequestContext<TParams>(new DestinationBoundMcpServer(this, jsonRpcRequest.Context?.RelatedTransport), jsonRpcRequest, args)
                     {
                         Services = scope?.ServiceProvider ?? Services,
-                        Params = args
                     },
                     cancellationToken).ConfigureAwait(false);
             }

src/ModelContextProtocol.Core/Server/RequestContext.cs

@@ -13,19 +13,34 @@ namespace ModelContextProtocol.Server;
 /// </remarks>
 public sealed class RequestContext<TParams> : MessageContext
 {
+    /// <summary>
+    /// Initializes a new instance of the <see cref="RequestContext{TParams}"/> class with the specified server, JSON-RPC request, and request parameters.
+    /// </summary>
+    /// <param name="server">The server with which this instance is associated.</param>
+    /// <param name="jsonRpcRequest">The JSON-RPC request associated with this context.</param>
+    /// <param name="parameters">The parameters associated with this request.</param>
+    /// <exception cref="ArgumentNullException"><paramref name="server"/> or <paramref name="jsonRpcRequest"/> is <see langword="null"/>.</exception>
+    public RequestContext(McpServer server, JsonRpcRequest jsonRpcRequest, TParams parameters)
+        : base(server, jsonRpcRequest)
+    {
+        Params = parameters;
+    }
+
     /// <summary>
     /// Initializes a new instance of the <see cref="RequestContext{TParams}"/> class with the specified server and JSON-RPC request.
     /// </summary>
     /// <param name="server">The server with which this instance is associated.</param>
     /// <param name="jsonRpcRequest">The JSON-RPC request associated with this context.</param>
     /// <exception cref="ArgumentNullException"><paramref name="server"/> or <paramref name="jsonRpcRequest"/> is <see langword="null"/>.</exception>
+    [Obsolete(Obsoletions.RequestContextParamsConstructor_Message, DiagnosticId = Obsoletions.RequestContextParamsConstructor_DiagnosticId, UrlFormat = Obsoletions.RequestContextParamsConstructor_Url)]
     public RequestContext(McpServer server, JsonRpcRequest jsonRpcRequest)
         : base(server, jsonRpcRequest)
     {
+        Params = default!;
     }
 
     /// <summary>Gets or sets the parameters associated with this request.</summary>
-    public TParams? Params { get; set; }
+    public TParams Params { get; set; }
 
     /// <summary>
     /// Gets or sets the primitive that matched the request.

tests/ModelContextProtocol.ConformanceServer/Program.cs

@@ -39,7 +39,7 @@ public static async Task MainAsync(string[] args, ILoggerProvider? loggerProvide
                 // For the test_reconnection tool, enable polling mode after the tool runs.
                 // This stores the result and closes the SSE stream, so the client
                 // must reconnect via GET with Last-Event-ID to retrieve the result.
-                if (request.Params?.Name == "test_reconnection")
+                if (request.Params.Name == "test_reconnection")
                 {
                     await request.EnablePollingAsync(TimeSpan.FromMilliseconds(500), cancellationToken);
                 }
@@ -54,7 +54,7 @@ public static async Task MainAsync(string[] args, ILoggerProvider? loggerProvide
                 {
                     throw new McpException("Cannot add subscription for server with null SessionId");
                 }
-                if (ctx.Params?.Uri is { } uri)
+                if (ctx.Params.Uri is { } uri)
                 {
                     var sessionSubscriptions = subscriptions.GetOrAdd(ctx.Server.SessionId, _ => new());
                     sessionSubscriptions.TryAdd(uri, 0);
@@ -68,7 +68,7 @@ public static async Task MainAsync(string[] args, ILoggerProvider? loggerProvide
                 {
                     throw new McpException("Cannot remove subscription for server with null SessionId");
                 }
-                if (ctx.Params?.Uri is { } uri)
+                if (ctx.Params.Uri is { } uri)
                 {
                     subscriptions[ctx.Server.SessionId].TryRemove(uri, out _);
                 }
@@ -91,11 +91,6 @@ public static async Task MainAsync(string[] args, ILoggerProvider? loggerProvide
             })
             .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 LoggingMessageNotificationParams

tests/ModelContextProtocol.ConformanceServer/Tools/ConformanceTools.cs

@@ -132,7 +132,7 @@ public static async Task<string> ToolWithProgress(
         RequestContext<CallToolRequestParams> context,
         CancellationToken cancellationToken)
     {
-        var progressToken = context.Params?.ProgressToken;
+        var progressToken = context.Params.ProgressToken;
 
         if (progressToken is not null)
         {