Add optional JsonSerializerOptions parameter to ToContentBlock and ToJsonObject

- Added optional JsonSerializerOptions parameter to ToContentBlock method
- Added optional JsonSerializerOptions parameter to ToJsonObject helper method
- Updated all serialization calls within ToContentBlock to use provided options
- Updated XML documentation references in McpServerTool and McpServerToolAttribute
- Added test to verify custom JsonSerializerOptions are properly used
- Enables user-defined serialization options to be passed through for anonymous types and custom converters

Co-authored-by: eiriktsarpalis <2813363+eiriktsarpalis@users.noreply.github.com>

Author: Copilot

src/ModelContextProtocol.Core/AIContentExtensions.cs

@@ -138,8 +138,11 @@ public static class AIContentExtensions
     }
 
     /// <summary>Converts the specified dictionary to a <see cref="JsonObject"/>.</summary>
-    internal static JsonObject? ToJsonObject(this IReadOnlyDictionary<string, object?> properties) =>
-        JsonSerializer.SerializeToNode(properties, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(IReadOnlyDictionary<string, object?>))) as JsonObject;
+    internal static JsonObject? ToJsonObject(this IReadOnlyDictionary<string, object?> properties, JsonSerializerOptions? options = null)
+    {
+        options ??= McpJsonUtilities.DefaultOptions;
+        return JsonSerializer.SerializeToNode(properties, options.GetTypeInfo(typeof(IReadOnlyDictionary<string, object?>))) as JsonObject;
+    }
 
     internal static AdditionalPropertiesDictionary ToAdditionalProperties(this JsonObject obj)
     {
@@ -365,12 +368,15 @@ public static IList<AIContent> ToAIContents(this IEnumerable<ResourceContents> c
 
     /// <summary>Creates a new <see cref="ContentBlock"/> from the content of an <see cref="AIContent"/>.</summary>
     /// <param name="content">The <see cref="AIContent"/> to convert.</param>
+    /// <param name="options">The <see cref="JsonSerializerOptions"/> to use for serialization. If <see langword="null"/>, <see cref="McpJsonUtilities.DefaultOptions"/> is used.</param>
     /// <returns>The created <see cref="ContentBlock"/>.</returns>
     /// <exception cref="ArgumentNullException"><paramref name="content"/> is <see langword="null"/>.</exception>
-    public static ContentBlock ToContentBlock(this AIContent content)
+    public static ContentBlock ToContentBlock(this AIContent content, JsonSerializerOptions? options = null)
     {
         Throw.IfNull(content);
 
+        options ??= McpJsonUtilities.DefaultOptions;
+
         ContentBlock contentBlock = content switch
         {
             TextContent textContent => new TextContentBlock
@@ -404,27 +410,27 @@ public static ContentBlock ToContentBlock(this AIContent content)
             {
                 Id = callContent.CallId,
                 Name = callContent.Name,
-                Input = JsonSerializer.SerializeToElement(callContent.Arguments, McpJsonUtilities.DefaultOptions.GetTypeInfo<IDictionary<string, object?>>()!),
+                Input = JsonSerializer.SerializeToElement(callContent.Arguments, options.GetTypeInfo<IDictionary<string, object?>>()!),
             },
 
             FunctionResultContent resultContent => new ToolResultContentBlock()
             {
                 ToolUseId = resultContent.CallId,
                 IsError = resultContent.Exception is not null,
                 Content =
-                    resultContent.Result is AIContent c ? [c.ToContentBlock()] :
-                    resultContent.Result is IEnumerable<AIContent> ec ? [.. ec.Select(c => c.ToContentBlock())] :
-                    [new TextContentBlock { Text = JsonSerializer.Serialize(content, McpJsonUtilities.DefaultOptions.GetTypeInfo<object>()) }],
+                    resultContent.Result is AIContent c ? [c.ToContentBlock(options)] :
+                    resultContent.Result is IEnumerable<AIContent> ec ? [.. ec.Select(c => c.ToContentBlock(options))] :
+                    [new TextContentBlock { Text = JsonSerializer.Serialize(content, options.GetTypeInfo<object>()) }],
                 StructuredContent = resultContent.Result is JsonElement je ? je : null,
             },
 
             _ => new TextContentBlock
             {
-                Text = JsonSerializer.Serialize(content, McpJsonUtilities.DefaultOptions.GetTypeInfo(typeof(object))),
+                Text = JsonSerializer.Serialize(content, options.GetTypeInfo(typeof(object))),
             }
         };
 
-        contentBlock.Meta = content.AdditionalProperties?.ToJsonObject();
+        contentBlock.Meta = content.AdditionalProperties?.ToJsonObject(options);
 
         return contentBlock;
     }

src/ModelContextProtocol.Core/Server/McpServerTool.cs

@@ -99,7 +99,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="AIContent"/></term>
-///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="string"/></term>
@@ -111,7 +111,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{AIContent}"/> of <see cref="AIContent"/></term>
-///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{ContentBlock}"/> of <see cref="ContentBlock"/></term>

src/ModelContextProtocol.Core/Server/McpServerToolAttribute.cs

@@ -90,7 +90,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="AIContent"/></term>
-///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Converted to a single <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="string"/></term>
@@ -106,7 +106,7 @@ namespace ModelContextProtocol.Server;
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{AIContent}"/> of <see cref="AIContent"/></term>
-///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent)"/>.</description>
+///     <description>Each <see cref="AIContent"/> is converted to a <see cref="ContentBlock"/> object using <see cref="AIContentExtensions.ToContentBlock(AIContent, JsonSerializerOptions)"/>.</description>
 ///   </item>
 ///   <item>
 ///     <term><see cref="IEnumerable{Content}"/> of <see cref="ContentBlock"/></term>

tests/ModelContextProtocol.Tests/AIContentExtensionsTests.cs

@@ -305,4 +305,36 @@ public void DataContent_ToContentBlock_WithAnonymousTypeInAdditionalProperties_P
         Assert.NotNull(imageBlock.Meta);
         Assert.True(imageBlock.Meta.ContainsKey("dimensions"));
     }
+
+    [Fact]
+    public void ToContentBlock_WithCustomSerializerOptions_UsesProvidedOptions()
+    {
+        if (!JsonSerializer.IsReflectionEnabledByDefault)
+        {
+            return;
+        }
+
+        // Create custom options with specific settings
+        var customOptions = new JsonSerializerOptions(McpJsonUtilities.DefaultOptions)
+        {
+            PropertyNamingPolicy = JsonNamingPolicy.SnakeCaseLower
+        };
+
+        AIContent c = new()
+        {
+            AdditionalProperties = new()
+            {
+                ["TestData"] = new { MyProperty = "value" }
+            }
+        };
+
+        var contentBlock = c.ToContentBlock(customOptions);
+
+        Assert.NotNull(contentBlock);
+        Assert.NotNull(contentBlock.Meta);
+        
+        // Verify that the custom naming policy was applied
+        var json = contentBlock.Meta.ToString();
+        Assert.Contains("my_property", json.ToLowerInvariant());
+    }
 }