Allow override of name and description of McpClientTool (#165)

Author: PederHP

src/ModelContextProtocol/Client/McpClientTool.cs

@@ -1,5 +1,6 @@
 using ModelContextProtocol.Protocol.Types;
 using ModelContextProtocol.Utils.Json;
+using ModelContextProtocol.Utils;
 using Microsoft.Extensions.AI;
 using System.Text.Json;
 
@@ -9,22 +10,51 @@ namespace ModelContextProtocol.Client;
 public sealed class McpClientTool : AIFunction
 {
     private readonly IMcpClient _client;
+    private readonly string _name;
+    private readonly string _description;
 
-    internal McpClientTool(IMcpClient client, Tool tool, JsonSerializerOptions serializerOptions)
+    internal McpClientTool(IMcpClient client, Tool tool, JsonSerializerOptions serializerOptions, string? name = null, string? description = null)
     {
         _client = client;
         ProtocolTool = tool;
         JsonSerializerOptions = serializerOptions;
+        _name = name ?? tool.Name;
+        _description = description ?? tool.Description ?? string.Empty;
+    }
+
+    /// <summary>
+    /// Creates a new instance of the tool with the specified name.
+    /// This is useful for optimizing the tool name for specific models or for prefixing the tool name with a (usually server-derived) namespace to avoid conflicts.
+    /// The server will still be called with the original tool name, so no mapping is required.
+    /// </summary>
+    /// <param name="name">The model-facing name to give the tool.</param>
+    /// <returns>Copy of this McpClientTool with the provided name</returns>
+    public McpClientTool WithName(string name)
+    {
+        return new McpClientTool(_client, ProtocolTool, JsonSerializerOptions, name, _description);
+    }
+
+    /// <summary>
+    /// Creates a new instance of the tool with the specified description.
+    /// This can be used to provide modified or additional (e.g. examples) context to the model about the tool.
+    /// This will in general require a hard-coded mapping in the client. 
+    /// It is not recommended to use this without running evaluations to ensure the model actually benefits from the custom description.
+    /// </summary>
+    /// <param name="description">The description to give the tool.</param>
+    /// <returns>Copy of this McpClientTool with the provided description</returns>
+    public McpClientTool WithDescription(string description)
+    {
+        return new McpClientTool(_client, ProtocolTool, JsonSerializerOptions, _name, description);
     }
 
     /// <summary>Gets the protocol <see cref="Tool"/> type for this instance.</summary>
     public Tool ProtocolTool { get; }
 
     /// <inheritdoc/>
-    public override string Name => ProtocolTool.Name;
+    public override string Name => _name;
 
     /// <inheritdoc/>
-    public override string Description => ProtocolTool.Description ?? string.Empty;
+    public override string Description => _description;
 
     /// <inheritdoc/>
     public override JsonElement JsonSchema => ProtocolTool.InputSchema;

tests/ModelContextProtocol.Tests/Client/McpClientExtensionsTests.cs

@@ -171,4 +171,32 @@ public async Task GetPromptsAsync_HonorsJsonSerializerOptions()
 
         await Assert.ThrowsAsync<NotSupportedException>(() => client.GetPromptAsync("Prompt", new Dictionary<string, object?> { ["i"] = 42 }, emptyOptions, cancellationToken: TestContext.Current.CancellationToken));
     }
+
+    [Fact]
+    public async Task WithName_ChangesToolName()
+    {
+        JsonSerializerOptions options = new(JsonSerializerOptions.Default);
+        IMcpClient client = await CreateMcpClientForServer();
+
+        var tool = (await client.ListToolsAsync(options, TestContext.Current.CancellationToken)).First();
+        var originalName = tool.Name;
+        var renamedTool = tool.WithName("RenamedTool");
+
+        Assert.NotNull(renamedTool);
+        Assert.Equal("RenamedTool", renamedTool.Name);
+        Assert.Equal(originalName, tool?.Name);
+    }
+
+    [Fact]
+    public async Task WithDescription_ChangesToolDescription()
+    {
+        JsonSerializerOptions options = new(JsonSerializerOptions.Default);
+        IMcpClient client = await CreateMcpClientForServer();
+        var tool = (await client.ListToolsAsync(options, TestContext.Current.CancellationToken)).FirstOrDefault();
+        var originalDescription = tool?.Description;
+        var redescribedTool = tool?.WithDescription("ToolWithNewDescription");
+        Assert.NotNull(redescribedTool);
+        Assert.Equal("ToolWithNewDescription", redescribedTool.Description);
+        Assert.Equal(originalDescription, tool?.Description);
+    }
 }