modelcontextprotocol · eiriktsarpalis · May 14, 2025 · May 13, 2025
diff --git a/Directory.Packages.props b/Directory.Packages.props
@@ -2,7 +2,7 @@
   <PropertyGroup>
     <ManagePackageVersionsCentrally>true</ManagePackageVersionsCentrally>
     <System10Version>10.0.0-preview.3.25171.5</System10Version>
-    <MicrosoftExtensionsAIVersion>9.4.4-preview.1.25259.16</MicrosoftExtensionsAIVersion>
+    <MicrosoftExtensionsAIVersion>9.5.0-preview.1.25262.9</MicrosoftExtensionsAIVersion>
   </PropertyGroup>
 
   <!-- Product dependencies netstandard -->
@@ -31,7 +31,7 @@
 
   <!-- Product dependencies shared -->
   <ItemGroup>
-    <PackageVersion Include="Microsoft.Extensions.AI.Abstractions" Version="9.4.4-preview.1.25259.16" />
+    <PackageVersion Include="Microsoft.Extensions.AI.Abstractions" Version="$(MicrosoftExtensionsAIVersion)" />
     <PackageVersion Include="Microsoft.Extensions.AI" Version="$(MicrosoftExtensionsAIVersion)" />
     <PackageVersion Include="System.Net.ServerSentEvents" Version="$(System10Version)" />
   </ItemGroup>

diff --git a/src/ModelContextProtocol/Configuration/McpServerBuilderExtensions.cs b/src/ModelContextProtocol/Configuration/McpServerBuilderExtensions.cs
@@ -48,7 +48,7 @@ public static partial class McpServerBuilderExtensions
             {
                 builder.Services.AddSingleton((Func<IServiceProvider, McpServerTool>)(toolMethod.IsStatic ?
                     services => McpServerTool.Create(toolMethod, options: new() { Services = services, SerializerOptions = serializerOptions }) :
-                    services => McpServerTool.Create(toolMethod, typeof(TToolType), new() { Services = services, SerializerOptions = serializerOptions })));
+                    services => McpServerTool.Create(toolMethod, static r => CreateTarget(r.Services, typeof(TToolType)), new() { Services = services, SerializerOptions = serializerOptions })));
             }
         }
 
@@ -105,7 +105,7 @@ public static IMcpServerBuilder WithTools(this IMcpServerBuilder builder, IEnume
                     {
                         builder.Services.AddSingleton((Func<IServiceProvider, McpServerTool>)(toolMethod.IsStatic ?
                             services => McpServerTool.Create(toolMethod, options: new() { Services = services , SerializerOptions = serializerOptions }) :
-                            services => McpServerTool.Create(toolMethod, toolType, new() { Services = services , SerializerOptions = serializerOptions })));
+                            services => McpServerTool.Create(toolMethod, r => CreateTarget(r.Services, toolType), new() { Services = services , SerializerOptions = serializerOptions })));
                     }
                 }
             }
@@ -188,7 +188,7 @@ where t.GetCustomAttribute<McpServerToolTypeAttribute>() is not null
             {
                 builder.Services.AddSingleton((Func<IServiceProvider, McpServerPrompt>)(promptMethod.IsStatic ?
                     services => McpServerPrompt.Create(promptMethod, options: new() { Services = services, SerializerOptions = serializerOptions }) :
-                    services => McpServerPrompt.Create(promptMethod, typeof(TPromptType), new() { Services = services, SerializerOptions = serializerOptions })));
+                    services => McpServerPrompt.Create(promptMethod, static r => CreateTarget(r.Services, typeof(TPromptType)), new() { Services = services, SerializerOptions = serializerOptions })));
             }
         }
 
@@ -245,7 +245,7 @@ public static IMcpServerBuilder WithPrompts(this IMcpServerBuilder builder, IEnu
                     {
                         builder.Services.AddSingleton((Func<IServiceProvider, McpServerPrompt>)(promptMethod.IsStatic ?
                             services => McpServerPrompt.Create(promptMethod, options: new() { Services = services, SerializerOptions = serializerOptions }) :
-                            services => McpServerPrompt.Create(promptMethod, promptType, new() { Services = services, SerializerOptions = serializerOptions })));
+                            services => McpServerPrompt.Create(promptMethod, r => CreateTarget(r.Services, promptType), new() { Services = services, SerializerOptions = serializerOptions })));
                     }
                 }
             }
@@ -325,7 +325,7 @@ where t.GetCustomAttribute<McpServerPromptTypeAttribute>() is not null
             {
                 builder.Services.AddSingleton((Func<IServiceProvider, McpServerResource>)(resourceTemplateMethod.IsStatic ?
                     services => McpServerResource.Create(resourceTemplateMethod, options: new() { Services = services }) :
-                    services => McpServerResource.Create(resourceTemplateMethod, typeof(TResourceType), new() { Services = services })));
+                    services => McpServerResource.Create(resourceTemplateMethod, static r => CreateTarget(r.Services, typeof(TResourceType)), new() { Services = services })));
             }
         }
 
@@ -381,7 +381,7 @@ public static IMcpServerBuilder WithResources(this IMcpServerBuilder builder, IE
                     {
                         builder.Services.AddSingleton((Func<IServiceProvider, McpServerResource>)(resourceTemplateMethod.IsStatic ?
                             services => McpServerResource.Create(resourceTemplateMethod, options: new() { Services = services }) :
-                            services => McpServerResource.Create(resourceTemplateMethod, resourceTemplateType, new() { Services = services })));
+                            services => McpServerResource.Create(resourceTemplateMethod, r => CreateTarget(r.Services, resourceTemplateType), new() { Services = services })));
                     }
                 }
             }
@@ -775,4 +775,13 @@ private static void AddSingleSessionServerDependencies(IServiceCollection servic
         });
     }
     #endregion
+
+    #region Helpers
+    /// <summary>Creates an instance of the target object.</summary>
+    private static object CreateTarget(
+        IServiceProvider? services,
+        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type type) =>
+        services is not null ? ActivatorUtilities.CreateInstance(services, type) :
+        Activator.CreateInstance(type)!;
+    #endregion
 }
diff --git a/src/ModelContextProtocol/Server/AIFunctionMcpServerPrompt.cs b/src/ModelContextProtocol/Server/AIFunctionMcpServerPrompt.cs
@@ -4,7 +4,6 @@
 using ModelContextProtocol.Utils;
 using ModelContextProtocol.Utils.Json;
 using System.ComponentModel;
-using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Text.Json;
 
@@ -49,15 +48,20 @@ internal sealed class AIFunctionMcpServerPrompt : McpServerPrompt
     /// </summary>
     public static new AIFunctionMcpServerPrompt Create(
         MethodInfo method,
-        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type targetType,
+        Func<RequestContext<GetPromptRequestParams>, object> createTargetFunc,
         McpServerPromptCreateOptions? options)
     {
         Throw.IfNull(method);
+        Throw.IfNull(createTargetFunc);
 
         options = DeriveOptions(method, options);
 
         return Create(
-            AIFunctionFactory.Create(method, targetType, CreateAIFunctionFactoryOptions(method, options)),
+            AIFunctionFactory.Create(method, args =>
+            {
+                var request = (RequestContext<GetPromptRequestParams>)args.Context![typeof(RequestContext<GetPromptRequestParams>)]!;
+                return createTargetFunc(request);
+            }, CreateAIFunctionFactoryOptions(method, options)),
             options);
     }
 
@@ -69,7 +73,6 @@ private static AIFunctionFactoryOptions CreateAIFunctionFactoryOptions(
             Description = options?.Description,
             MarshalResult = static (result, _, cancellationToken) => new ValueTask<object?>(result),
             SerializerOptions = options?.SerializerOptions ?? McpJsonUtilities.DefaultOptions,
-            CreateInstance = AIFunctionMcpServerTool.GetCreateInstanceFunc(),
             ConfigureParameterBinding = pi =>
             {
                 if (pi.ParameterType == typeof(RequestContext<GetPromptRequestParams>))

diff --git a/src/ModelContextProtocol/Server/AIFunctionMcpServerResource.cs b/src/ModelContextProtocol/Server/AIFunctionMcpServerResource.cs
@@ -5,7 +5,6 @@
 using ModelContextProtocol.Utils.Json;
 using System.Collections.Concurrent;
 using System.ComponentModel;
-using System.Diagnostics.CodeAnalysis;
 using System.Globalization;
 using System.Reflection;
 using System.Text;
@@ -56,15 +55,20 @@ internal sealed class AIFunctionMcpServerResource : McpServerResource
     /// </summary>
     public static new AIFunctionMcpServerResource Create(
         MethodInfo method,
-        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type targetType,
+        Func<RequestContext<ReadResourceRequestParams>, object> createTargetFunc,
         McpServerResourceCreateOptions? options)
     {
         Throw.IfNull(method);
+        Throw.IfNull(createTargetFunc);
 
         options = DeriveOptions(method, options);
 
         return Create(
-            AIFunctionFactory.Create(method, targetType, CreateAIFunctionFactoryOptions(method, options)),
+            AIFunctionFactory.Create(method, args =>
+            {
+                var request = (RequestContext<ReadResourceRequestParams>)args.Context![typeof(RequestContext<ReadResourceRequestParams>)]!;
+                return createTargetFunc(request);
+            }, CreateAIFunctionFactoryOptions(method, options)),
             options);
     }
 
@@ -76,7 +80,6 @@ private static AIFunctionFactoryOptions CreateAIFunctionFactoryOptions(
             Description = options?.Description,
             MarshalResult = static (result, _, cancellationToken) => new ValueTask<object?>(result),
             SerializerOptions = McpJsonUtilities.DefaultOptions,
-            CreateInstance = AIFunctionMcpServerTool.GetCreateInstanceFunc(),
             ConfigureParameterBinding = pi =>
             {
                 if (pi.ParameterType == typeof(RequestContext<ReadResourceRequestParams>))

diff --git a/src/ModelContextProtocol/Server/AIFunctionMcpServerTool.cs b/src/ModelContextProtocol/Server/AIFunctionMcpServerTool.cs
@@ -49,15 +49,20 @@ internal sealed class AIFunctionMcpServerTool : McpServerTool
     /// </summary>
     public static new AIFunctionMcpServerTool Create(
         MethodInfo method,
-        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type targetType,
+        Func<RequestContext<CallToolRequestParams>, object> createTargetFunc,
         McpServerToolCreateOptions? options)
     {
         Throw.IfNull(method);
+        Throw.IfNull(createTargetFunc);
 
         options = DeriveOptions(method, options);
 
         return Create(
-            AIFunctionFactory.Create(method, targetType, CreateAIFunctionFactoryOptions(method, options)),
+            AIFunctionFactory.Create(method, args =>
+            {
+                var request = (RequestContext<CallToolRequestParams>)args.Context![typeof(RequestContext<CallToolRequestParams>)]!;
+                return createTargetFunc(request);
+            }, CreateAIFunctionFactoryOptions(method, options)),
             options);
     }
 
@@ -77,7 +82,6 @@ private static AIFunctionFactoryOptions CreateAIFunctionFactoryOptions(
             Description = options?.Description,
             MarshalResult = static (result, _, cancellationToken) => new ValueTask<object?>(result),
             SerializerOptions = options?.SerializerOptions ?? McpJsonUtilities.DefaultOptions,
-            CreateInstance = GetCreateInstanceFunc(),
             ConfigureParameterBinding = pi =>
             {
                 if (pi.ParameterType == typeof(RequestContext<CallToolRequestParams>))

diff --git a/src/ModelContextProtocol/Server/McpServerPrompt.cs b/src/ModelContextProtocol/Server/McpServerPrompt.cs
@@ -3,7 +3,6 @@
 using ModelContextProtocol.Client;
 using ModelContextProtocol.Protocol.Messages;
 using ModelContextProtocol.Protocol.Types;
-using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Text.Json;
 
@@ -184,21 +183,19 @@ public static McpServerPrompt Create(
     /// instantiate each time the method is invoked.
     /// </summary>
     /// <param name="method">The instance method to be represented via the created <see cref="AIFunction"/>.</param>
-    /// <param name="targetType">
-    /// The <see cref="Type"/> to construct an instance of on which to invoke <paramref name="method"/> when
-    /// the resulting <see cref="AIFunction"/> is invoked. If services are provided,
-    /// ActivatorUtilities.CreateInstance will be used to construct the instance using those services; otherwise,
-    /// <see cref="Activator.CreateInstance(Type)"/> is used, utilizing the type's public parameterless constructor.
-    /// If an instance can't be constructed, an exception is thrown during the function's invocation.
+    /// <param name="createTargetFunc">
+    /// Callback used on each function invocation to create an instance of the type on which the instance method <paramref name="method"/>
+    /// will be invoked. If the returned instance is <see cref="IAsyncDisposable"/> or <see cref="IDisposable"/>, it will
+    /// be disposed of after method completes its invocation.
     /// </param>
     /// <param name="options">Optional options used in the creation of the <see cref="McpServerPrompt"/> to control its behavior.</param>
     /// <returns>The created <see cref="AIFunction"/> for invoking <paramref name="method"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="method"/> is <see langword="null"/>.</exception>
     public static McpServerPrompt Create(
         MethodInfo method,
-        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type targetType,
+        Func<RequestContext<GetPromptRequestParams>, object> createTargetFunc,
         McpServerPromptCreateOptions? options = null) =>
-        AIFunctionMcpServerPrompt.Create(method, targetType, options);
+        AIFunctionMcpServerPrompt.Create(method, createTargetFunc, options);
 
     /// <summary>Creates an <see cref="McpServerPrompt"/> that wraps the specified <see cref="AIFunction"/>.</summary>
     /// <param name="function">The function to wrap.</param>

diff --git a/src/ModelContextProtocol/Server/McpServerResource.cs b/src/ModelContextProtocol/Server/McpServerResource.cs
@@ -2,7 +2,6 @@
 using Microsoft.Extensions.DependencyInjection;
 using ModelContextProtocol.Protocol.Messages;
 using ModelContextProtocol.Protocol.Types;
-using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 
 namespace ModelContextProtocol.Server;
@@ -205,21 +204,19 @@ public static McpServerResource Create(
     /// instantiate each time the method is invoked.
     /// </summary>
     /// <param name="method">The instance method to be represented via the created <see cref="AIFunction"/>.</param>
-    /// <param name="targetType">
-    /// The <see cref="Type"/> to construct an instance of on which to invoke <paramref name="method"/> when
-    /// the resulting <see cref="AIFunction"/> is invoked. If services are provided,
-    /// ActivatorUtilities.CreateInstance will be used to construct the instance using those services; otherwise,
-    /// <see cref="Activator.CreateInstance(Type)"/> is used, utilizing the type's public parameterless constructor.
-    /// If an instance can't be constructed, an exception is thrown during the function's invocation.
+    /// <param name="createTargetFunc">
+    /// Callback used on each function invocation to create an instance of the type on which the instance method <paramref name="method"/>
+    /// will be invoked. If the returned instance is <see cref="IAsyncDisposable"/> or <see cref="IDisposable"/>, it will
+    /// be disposed of after method completes its invocation.
     /// </param>
     /// <param name="options">Optional options used in the creation of the <see cref="McpServerResource"/> to control its behavior.</param>
     /// <returns>The created <see cref="AIFunction"/> for invoking <paramref name="method"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="method"/> is <see langword="null"/>.</exception>
     public static McpServerResource Create(
         MethodInfo method,
-        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type targetType,
+        Func<RequestContext<ReadResourceRequestParams>, object> createTargetFunc,
         McpServerResourceCreateOptions? options = null) =>
-        AIFunctionMcpServerResource.Create(method, targetType, options);
+        AIFunctionMcpServerResource.Create(method, createTargetFunc, options);
 
     /// <summary>Creates an <see cref="McpServerResource"/> that wraps the specified <see cref="AIFunction"/>.</summary>
     /// <param name="function">The function to wrap.</param>

diff --git a/src/ModelContextProtocol/Server/McpServerTool.cs b/src/ModelContextProtocol/Server/McpServerTool.cs
@@ -4,7 +4,6 @@
 using ModelContextProtocol.Protocol.Messages;
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Utils.Json;
-using System.Diagnostics.CodeAnalysis;
 using System.Reflection;
 using System.Text.Json;
 
@@ -187,21 +186,19 @@ public static McpServerTool Create(
     /// instantiate each time the method is invoked.
     /// </summary>
     /// <param name="method">The instance method to be represented via the created <see cref="AIFunction"/>.</param>
-    /// <param name="targetType">
-    /// The <see cref="Type"/> to construct an instance of on which to invoke <paramref name="method"/> when
-    /// the resulting <see cref="AIFunction"/> is invoked. If services are provided,
-    /// ActivatorUtilities.CreateInstance will be used to construct the instance using those services; otherwise,
-    /// <see cref="Activator.CreateInstance(Type)"/> is used, utilizing the type's public parameterless constructor.
-    /// If an instance can't be constructed, an exception is thrown during the function's invocation.
+    /// <param name="createTargetFunc">
+    /// Callback used on each function invocation to create an instance of the type on which the instance method <paramref name="method"/>
+    /// will be invoked. If the returned instance is <see cref="IAsyncDisposable"/> or <see cref="IDisposable"/>, it will
+    /// be disposed of after method completes its invocation.
     /// </param>
     /// <param name="options">Optional options used in the creation of the <see cref="McpServerTool"/> to control its behavior.</param>
     /// <returns>The created <see cref="AIFunction"/> for invoking <paramref name="method"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="method"/> is <see langword="null"/>.</exception>
     public static McpServerTool Create(
         MethodInfo method,
-        [DynamicallyAccessedMembers(DynamicallyAccessedMemberTypes.PublicConstructors)] Type targetType,
+        Func<RequestContext<CallToolRequestParams>, object> createTargetFunc,
         McpServerToolCreateOptions? options = null) =>
-        AIFunctionMcpServerTool.Create(method, targetType, options);
+        AIFunctionMcpServerTool.Create(method, createTargetFunc, options);
 
     /// <summary>Creates an <see cref="McpServerTool"/> that wraps the specified <see cref="AIFunction"/>.</summary>
     /// <param name="function">The function to wrap.</param>

diff --git a/tests/ModelContextProtocol.Tests/Server/McpServerPromptTests.cs b/tests/ModelContextProtocol.Tests/Server/McpServerPromptTests.cs
@@ -15,8 +15,8 @@ public void Create_InvalidArgs_Throws()
     {
         Assert.Throws<ArgumentNullException>("function", () => McpServerPrompt.Create((AIFunction)null!));
         Assert.Throws<ArgumentNullException>("method", () => McpServerPrompt.Create((MethodInfo)null!));
-        Assert.Throws<ArgumentNullException>("method", () => McpServerPrompt.Create((MethodInfo)null!, typeof(object)));
-        Assert.Throws<ArgumentNullException>("targetType", () => McpServerPrompt.Create(typeof(McpServerPromptTests).GetMethod(nameof(Create_InvalidArgs_Throws))!, (Type)null!));
+        Assert.Throws<ArgumentNullException>("method", () => McpServerPrompt.Create((MethodInfo)null!, _ => new object()));
+        Assert.Throws<ArgumentNullException>("createTargetFunc", () => McpServerPrompt.Create(typeof(McpServerPromptTests).GetMethod(nameof(Create_InvalidArgs_Throws))!, null!));
         Assert.Throws<ArgumentNullException>("method", () => McpServerPrompt.Create((Delegate)null!));
     }
 
@@ -96,7 +96,7 @@ public async Task SupportsDisposingInstantiatedDisposableTargets()
     {
         McpServerPrompt prompt1 = McpServerPrompt.Create(
             typeof(DisposablePromptType).GetMethod(nameof(DisposablePromptType.InstanceMethod))!,
-            typeof(DisposablePromptType));
+            _ => new DisposablePromptType());
 
         var result = await prompt1.GetAsync(
             new RequestContext<GetPromptRequestParams>(new Mock<IMcpServer>().Object),
@@ -109,7 +109,7 @@ public async Task SupportsAsyncDisposingInstantiatedAsyncDisposableTargets()
     {
         McpServerPrompt prompt1 = McpServerPrompt.Create(
             typeof(AsyncDisposablePromptType).GetMethod(nameof(AsyncDisposablePromptType.InstanceMethod))!,
-            typeof(AsyncDisposablePromptType));
+            _ => new AsyncDisposablePromptType());
 
         var result = await prompt1.GetAsync(
             new RequestContext<GetPromptRequestParams>(new Mock<IMcpServer>().Object),
@@ -122,7 +122,7 @@ public async Task SupportsAsyncDisposingInstantiatedAsyncDisposableAndDisposable
     {
         McpServerPrompt prompt1 = McpServerPrompt.Create(
             typeof(AsyncDisposableAndDisposablePromptType).GetMethod(nameof(AsyncDisposableAndDisposablePromptType.InstanceMethod))!,
-            typeof(AsyncDisposableAndDisposablePromptType));
+            _ => new AsyncDisposableAndDisposablePromptType());
 
         var result = await prompt1.GetAsync(
             new RequestContext<GetPromptRequestParams>(new Mock<IMcpServer>().Object),

diff --git a/tests/ModelContextProtocol.Tests/Server/McpServerResourceTests.cs b/tests/ModelContextProtocol.Tests/Server/McpServerResourceTests.cs
@@ -109,8 +109,8 @@ public void Create_InvalidArgs_Throws()
     {
         Assert.Throws<ArgumentNullException>("function", () => McpServerResource.Create((AIFunction)null!, new() { UriTemplate = "test://hello" }));
         Assert.Throws<ArgumentNullException>("method", () => McpServerResource.Create((MethodInfo)null!));
-        Assert.Throws<ArgumentNullException>("method", () => McpServerResource.Create((MethodInfo)null!, typeof(object)));
-        Assert.Throws<ArgumentNullException>("targetType", () => McpServerResource.Create(typeof(McpServerResourceTests).GetMethod(nameof(Create_InvalidArgs_Throws))!, (Type)null!));
+        Assert.Throws<ArgumentNullException>("method", () => McpServerResource.Create((MethodInfo)null!, _ => new object()));
+        Assert.Throws<ArgumentNullException>("createTargetFunc", () => McpServerResource.Create(typeof(McpServerResourceTests).GetMethod(nameof(Create_InvalidArgs_Throws))!, null!));
         Assert.Throws<ArgumentNullException>("method", () => McpServerResource.Create((Delegate)null!));
 
         Assert.NotNull(McpServerResource.Create(typeof(DisposableResourceType).GetMethod(nameof(DisposableResourceType.InstanceMethod))!, new DisposableResourceType()));
@@ -415,7 +415,7 @@ public async Task SupportsDisposingInstantiatedDisposableTargets()
 
         McpServerResource resource1 = McpServerResource.Create(
             typeof(DisposableResourceType).GetMethod(nameof(DisposableResourceType.InstanceMethod))!,
-            typeof(DisposableResourceType));
+            _ => new DisposableResourceType());
 
         var result = await resource1.ReadAsync(
             new RequestContext<ReadResourceRequestParams>(new Mock<IMcpServer>().Object) { Params = new() { Uri = "test://static/resource/instanceMethod" } },

diff --git a/tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs b/tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs
@@ -18,7 +18,7 @@ public void Create_InvalidArgs_Throws()
         Assert.Throws<ArgumentNullException>("function", () => McpServerTool.Create((AIFunction)null!));
         Assert.Throws<ArgumentNullException>("method", () => McpServerTool.Create((MethodInfo)null!));
         Assert.Throws<ArgumentNullException>("method", () => McpServerTool.Create((MethodInfo)null!, typeof(object)));
-        Assert.Throws<ArgumentNullException>("targetType", () => McpServerTool.Create(typeof(McpServerToolTests).GetMethod(nameof(Create_InvalidArgs_Throws))!, (Type)null!));
+        Assert.Throws<ArgumentNullException>("createTargetFunc", () => McpServerTool.Create(typeof(McpServerToolTests).GetMethod(nameof(Create_InvalidArgs_Throws))!, null!));
         Assert.Throws<ArgumentNullException>("method", () => McpServerTool.Create((Delegate)null!));
 
         Assert.NotNull(McpServerTool.Create(typeof(DisposableToolType).GetMethod(nameof(DisposableToolType.InstanceMethod))!, new DisposableToolType()));
@@ -129,7 +129,7 @@ public async Task SupportsDisposingInstantiatedDisposableTargets()
         McpServerToolCreateOptions options = new() { SerializerOptions = JsonContext2.Default.Options };
         McpServerTool tool1 = McpServerTool.Create(
             typeof(DisposableToolType).GetMethod(nameof(DisposableToolType.InstanceMethod))!,
-            typeof(DisposableToolType),
+            _ => new DisposableToolType(),
             options);
 
         var result = await tool1.InvokeAsync(
@@ -144,7 +144,7 @@ public async Task SupportsAsyncDisposingInstantiatedAsyncDisposableTargets()
         McpServerToolCreateOptions options = new() { SerializerOptions = JsonContext2.Default.Options };
         McpServerTool tool1 = McpServerTool.Create(
             typeof(AsyncDisposableToolType).GetMethod(nameof(AsyncDisposableToolType.InstanceMethod))!,
-            typeof(AsyncDisposableToolType),
+            _ => new AsyncDisposableToolType(),
             options);
 
         var result = await tool1.InvokeAsync(
@@ -163,7 +163,7 @@ public async Task SupportsAsyncDisposingInstantiatedAsyncDisposableAndDisposable
         McpServerToolCreateOptions options = new() { SerializerOptions = JsonContext2.Default.Options };
         McpServerTool tool1 = McpServerTool.Create(
             typeof(AsyncDisposableAndDisposableToolType).GetMethod(nameof(AsyncDisposableAndDisposableToolType.InstanceMethod))!,
-            typeof(AsyncDisposableAndDisposableToolType),
+            static r => ActivatorUtilities.CreateInstance(r.Services!, typeof(AsyncDisposableAndDisposableToolType)),
             options);
 
         var result = await tool1.InvokeAsync(