Add Meta property to options classes and update logic to merge with attributes

Co-authored-by: stephentoub <[email protected]>

Author: Copilot

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerPrompt.cs

@@ -138,10 +138,14 @@ private static AIFunctionFactoryOptions CreateAIFunctionFactoryOptions(
             Icons = options?.Icons,
         };
 
-        // Populate Meta from McpMetaAttribute instances if a MethodInfo is in the metadata
+        // Populate Meta from options and/or McpMetaAttribute instances if a MethodInfo is in the metadata
         if (options?.Metadata?.FirstOrDefault(m => m is MethodInfo) is MethodInfo method)
         {
-            prompt.Meta = AIFunctionMcpServerTool.CreateMetaFromAttributes(method);
+            prompt.Meta = AIFunctionMcpServerTool.CreateMetaFromAttributes(method, options.Meta);
+        }
+        else if (options?.Meta is not null)
+        {
+            prompt.Meta = options.Meta;
         }
 
         return new AIFunctionMcpServerPrompt(function, prompt, options?.Metadata ?? []);

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerResource.cs

@@ -211,11 +211,15 @@ private static AIFunctionFactoryOptions CreateAIFunctionFactoryOptions(
 
         string name = options?.Name ?? function.Name;
 
-        // Populate Meta from McpMetaAttribute instances if a MethodInfo is in the metadata
+        // Populate Meta from options and/or McpMetaAttribute instances if a MethodInfo is in the metadata
         JsonObject? meta = null;
         if (options?.Metadata?.FirstOrDefault(m => m is MethodInfo) is MethodInfo method)
         {
-            meta = AIFunctionMcpServerTool.CreateMetaFromAttributes(method);
+            meta = AIFunctionMcpServerTool.CreateMetaFromAttributes(method, options.Meta);
+        }
+        else if (options?.Meta is not null)
+        {
+            meta = options.Meta;
         }
 
         ResourceTemplate resource = new()

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs

@@ -144,10 +144,14 @@ options.OpenWorld is not null ||
                 };
             }
 
-            // Populate Meta from McpMetaAttribute instances if a MethodInfo is in the metadata
+            // Populate Meta from options and/or McpMetaAttribute instances if a MethodInfo is in the metadata
             if (options.Metadata?.FirstOrDefault(m => m is MethodInfo) is MethodInfo method)
             {
-                tool.Meta = CreateMetaFromAttributes(method);
+                tool.Meta = CreateMetaFromAttributes(method, options.Meta);
+            }
+            else if (options.Meta is not null)
+            {
+                tool.Meta = options.Meta;
             }
         }
 
@@ -358,16 +362,23 @@ internal static IReadOnlyList<object> CreateMetadata(MethodInfo method)
     }
 
     /// <summary>Creates a Meta JsonObject from McpMetaAttribute instances on the specified method.</summary>
-    internal static JsonObject? CreateMetaFromAttributes(MethodInfo method)
+    /// <param name="method">The method to extract McpMetaAttribute instances from.</param>
+    /// <param name="seedMeta">Optional JsonObject to seed the Meta with. Properties from this object take precedence over attributes.</param>
+    /// <returns>A JsonObject with metadata, or null if no metadata is present.</returns>
+    internal static JsonObject? CreateMetaFromAttributes(MethodInfo method, JsonObject? seedMeta = null)
     {
         // Get all McpMetaAttribute instances from the method
         var metaAttributes = method.GetCustomAttributes<McpMetaAttribute>();
 
-        JsonObject? meta = null;
+        JsonObject? meta = seedMeta;
         foreach (var attr in metaAttributes)
         {
             meta ??= new JsonObject();
-            meta[attr.Name] = attr.Value;
+            // Only add the attribute property if it doesn't already exist in the seed
+            if (!meta.ContainsKey(attr.Name))
+            {
+                meta[attr.Name] = attr.Value;
+            }
         }
 
         return meta;

src/ModelContextProtocol.Core/Server/McpServerPromptCreateOptions.cs

@@ -86,6 +86,21 @@ public sealed class McpServerPromptCreateOptions
     /// </remarks>
     public IList<Icon>? Icons { get; set; }
 
+    /// <summary>
+    /// Gets or sets metadata reserved by MCP for protocol-level metadata.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This JsonObject is used to seed the <see cref="Prompt.Meta"/> property. Any metadata from
+    /// <see cref="McpMetaAttribute"/> instances on the method will be added to this object, but
+    /// properties already present in this JsonObject will not be overwritten.
+    /// </para>
+    /// <para>
+    /// Implementations must not make assumptions about its contents.
+    /// </para>
+    /// </remarks>
+    public System.Text.Json.Nodes.JsonObject? Meta { get; set; }
+
     /// <summary>
     /// Creates a shallow clone of the current <see cref="McpServerPromptCreateOptions"/> instance.
     /// </summary>
@@ -100,5 +115,6 @@ internal McpServerPromptCreateOptions Clone() =>
             SchemaCreateOptions = SchemaCreateOptions,
             Metadata = Metadata,
             Icons = Icons,
+            Meta = Meta,
         };
 }

src/ModelContextProtocol.Core/Server/McpServerResourceCreateOptions.cs

@@ -101,6 +101,21 @@ public sealed class McpServerResourceCreateOptions
     /// </remarks>
     public IList<Icon>? Icons { get; set; }
 
+    /// <summary>
+    /// Gets or sets metadata reserved by MCP for protocol-level metadata.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This JsonObject is used to seed the <see cref="Resource.Meta"/> property. Any metadata from
+    /// <see cref="McpMetaAttribute"/> instances on the method will be added to this object, but
+    /// properties already present in this JsonObject will not be overwritten.
+    /// </para>
+    /// <para>
+    /// Implementations must not make assumptions about its contents.
+    /// </para>
+    /// </remarks>
+    public System.Text.Json.Nodes.JsonObject? Meta { get; set; }
+
     /// <summary>
     /// Creates a shallow clone of the current <see cref="McpServerResourceCreateOptions"/> instance.
     /// </summary>
@@ -117,5 +132,6 @@ internal McpServerResourceCreateOptions Clone() =>
             SchemaCreateOptions = SchemaCreateOptions,
             Metadata = Metadata,
             Icons = Icons,
+            Meta = Meta,
         };
 }

src/ModelContextProtocol.Core/Server/McpServerToolCreateOptions.cs

@@ -172,6 +172,21 @@ public sealed class McpServerToolCreateOptions
     /// </remarks>
     public IList<Icon>? Icons { get; set; }
 
+    /// <summary>
+    /// Gets or sets metadata reserved by MCP for protocol-level metadata.
+    /// </summary>
+    /// <remarks>
+    /// <para>
+    /// This JsonObject is used to seed the <see cref="Tool.Meta"/> property. Any metadata from
+    /// <see cref="McpMetaAttribute"/> instances on the method will be added to this object, but
+    /// properties already present in this JsonObject will not be overwritten.
+    /// </para>
+    /// <para>
+    /// Implementations must not make assumptions about its contents.
+    /// </para>
+    /// </remarks>
+    public System.Text.Json.Nodes.JsonObject? Meta { get; set; }
+
     /// <summary>
     /// Creates a shallow clone of the current <see cref="McpServerToolCreateOptions"/> instance.
     /// </summary>
@@ -191,5 +206,6 @@ internal McpServerToolCreateOptions Clone() =>
             SchemaCreateOptions = SchemaCreateOptions,
             Metadata = Metadata,
             Icons = Icons,
+            Meta = Meta,
         };
 }

tests/ModelContextProtocol.Tests/Server/McpMetaAttributeTests.cs

@@ -80,6 +80,101 @@ public void McpMetaAttribute_SingleAttribute_PopulatesMeta()
         Assert.Single(tool.ProtocolTool.Meta);
     }
 
+    [Fact]
+    public void McpMetaAttribute_OptionsMetaTakesPrecedence()
+    {
+        // Arrange
+        var method = typeof(TestToolClass).GetMethod(nameof(TestToolClass.ToolWithMeta))!;
+        var seedMeta = new JsonObject
+        {
+            ["model"] = "options-model",
+            ["extra"] = "options-extra"
+        };
+        var options = new McpServerToolCreateOptions { Meta = seedMeta };
+        
+        // Act
+        var tool = McpServerTool.Create(method, options);
+        
+        // Assert
+        Assert.NotNull(tool.ProtocolTool.Meta);
+        // Options Meta should win for "model"
+        Assert.Equal("options-model", tool.ProtocolTool.Meta["model"]?.ToString());
+        // Attribute should add "version" since it's not in options
+        Assert.Equal("1.0", tool.ProtocolTool.Meta["version"]?.ToString());
+        // Options Meta should include "extra"
+        Assert.Equal("options-extra", tool.ProtocolTool.Meta["extra"]?.ToString());
+    }
+
+    [Fact]
+    public void McpMetaAttribute_OptionsMetaOnly_NoAttributes()
+    {
+        // Arrange
+        var method = typeof(TestToolClass).GetMethod(nameof(TestToolClass.ToolWithoutMeta))!;
+        var seedMeta = new JsonObject
+        {
+            ["custom"] = "value"
+        };
+        var options = new McpServerToolCreateOptions { Meta = seedMeta };
+        
+        // Act
+        var tool = McpServerTool.Create(method, options);
+        
+        // Assert
+        Assert.NotNull(tool.ProtocolTool.Meta);
+        Assert.Equal("value", tool.ProtocolTool.Meta["custom"]?.ToString());
+        Assert.Single(tool.ProtocolTool.Meta);
+    }
+
+    [Fact]
+    public void McpMetaAttribute_PromptOptionsMetaTakesPrecedence()
+    {
+        // Arrange
+        var method = typeof(TestPromptClass).GetMethod(nameof(TestPromptClass.PromptWithMeta))!;
+        var seedMeta = new JsonObject
+        {
+            ["type"] = "options-type",
+            ["extra"] = "options-extra"
+        };
+        var options = new McpServerPromptCreateOptions { Meta = seedMeta };
+        
+        // Act
+        var prompt = McpServerPrompt.Create(method, options);
+        
+        // Assert
+        Assert.NotNull(prompt.ProtocolPrompt.Meta);
+        // Options Meta should win for "type"
+        Assert.Equal("options-type", prompt.ProtocolPrompt.Meta["type"]?.ToString());
+        // Attribute should add "model" since it's not in options
+        Assert.Equal("claude-3", prompt.ProtocolPrompt.Meta["model"]?.ToString());
+        // Options Meta should include "extra"
+        Assert.Equal("options-extra", prompt.ProtocolPrompt.Meta["extra"]?.ToString());
+    }
+
+    [Fact]
+    public void McpMetaAttribute_ResourceOptionsMetaTakesPrecedence()
+    {
+        // Arrange
+        var method = typeof(TestResourceClass).GetMethod(nameof(TestResourceClass.ResourceWithMeta))!;
+        var seedMeta = new JsonObject
+        {
+            ["encoding"] = "options-encoding",
+            ["extra"] = "options-extra"
+        };
+        var options = new McpServerResourceCreateOptions { Meta = seedMeta };
+        
+        // Act
+        var resource = McpServerResource.Create(method, options);
+        
+        // Assert
+        Assert.NotNull(resource.ProtocolResource.Meta);
+        // Options Meta should win for "encoding"
+        Assert.Equal("options-encoding", resource.ProtocolResource.Meta["encoding"]?.ToString());
+        // Attribute should add "caching" since it's not in options
+        Assert.Equal("cached", resource.ProtocolResource.Meta["caching"]?.ToString());
+        // Options Meta should include "extra"
+        Assert.Equal("options-extra", resource.ProtocolResource.Meta["extra"]?.ToString());
+    }
+
     private class TestToolClass
     {
         [McpServerTool]