Add DebuggerDisplay attributes to Protocol types (#1068)

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: stephentoub <2642209+stephentoub@users.noreply.github.com>
Co-authored-by: Stephen Halter <halter73@gmail.com>

src/ModelContextProtocol.Core/Protocol/BlobResourceContents.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol;
@@ -20,6 +21,7 @@ namespace ModelContextProtocol.Protocol;
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for more details.
 /// </para>
 /// </remarks>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class BlobResourceContents : ResourceContents
 {
     /// <summary>
@@ -27,4 +29,15 @@ public sealed class BlobResourceContents : ResourceContents
     /// </summary>
     [JsonPropertyName("blob")]
     public required string Blob { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            string lengthDisplay = DebuggerDisplayHelper.GetBase64LengthDisplay(Blob);
+            string mimeInfo = MimeType is not null ? $", MimeType = {MimeType}" : "";
+            return $"Uri = \"{Uri}\"{mimeInfo}, Length = {lengthDisplay}";
+        }
+    }
 }

src/ModelContextProtocol.Core/Protocol/ContentBlock.cs

@@ -356,6 +356,7 @@ public abstract class ContentBlock
 }
 
 /// <summary>Represents text provided to or from an LLM.</summary>
+[DebuggerDisplay("Text = \"{Text}\"")]
 public sealed class TextContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -366,9 +367,13 @@ public sealed class TextContentBlock : ContentBlock
     /// </summary>
     [JsonPropertyName("text")]
     public required string Text { get; set; }
+
+    /// <inheritdoc/>
+    public override string ToString() => Text ?? "";
 }
 
 /// <summary>Represents an image provided to or from an LLM.</summary>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class ImageContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -388,9 +393,13 @@ public sealed class ImageContentBlock : ContentBlock
     /// </remarks>
     [JsonPropertyName("mimeType")]
     public required string MimeType { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay => $"MimeType = {MimeType}, Length = {DebuggerDisplayHelper.GetBase64LengthDisplay(Data)}";
 }
 
 /// <summary>Represents audio provided to or from an LLM.</summary>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class AudioContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -410,12 +419,16 @@ public sealed class AudioContentBlock : ContentBlock
     /// </remarks>
     [JsonPropertyName("mimeType")]
     public required string MimeType { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay => $"MimeType = {MimeType}, Length = {DebuggerDisplayHelper.GetBase64LengthDisplay(Data)}";
 }
 
 /// <summary>Represents the contents of a resource, embedded into a prompt or tool call result.</summary>
 /// <remarks>
 /// It is up to the client how best to render embedded resources for the benefit of the LLM and/or the user.
 /// </remarks>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class EmbeddedResourceBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -433,12 +446,16 @@ public sealed class EmbeddedResourceBlock : ContentBlock
     /// </remarks>
     [JsonPropertyName("resource")]
     public required ResourceContents Resource { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay => $"Uri = \"{Resource.Uri}\"";
 }
 
 /// <summary>Represents a resource that the server is capable of reading, included in a prompt or tool call result.</summary>
 /// <remarks>
 /// Resource links returned by tools are not guaranteed to appear in the results of `resources/list` requests.
 /// </remarks>
+[DebuggerDisplay("Name = {Name}, Uri = \"{Uri}\"")]
 public sealed class ResourceLinkBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -503,6 +520,7 @@ public sealed class ResourceLinkBlock : ContentBlock
 }
 
 /// <summary>Represents a request from the assistant to call a tool.</summary>
+[DebuggerDisplay("Name = {Name}, Id = {Id}")]
 public sealed class ToolUseContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -531,6 +549,7 @@ public sealed class ToolUseContentBlock : ContentBlock
 }
 
 /// <summary>Represents the result of a tool use, provided by the user back to the assistant.</summary>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class ToolResultContentBlock : ContentBlock
 {
     /// <inheritdoc/>
@@ -575,4 +594,37 @@ public sealed class ToolResultContentBlock : ContentBlock
     /// </remarks>
     [JsonPropertyName("isError")]
     public bool? IsError { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            if (IsError == true)
+            {
+                return $"ToolUseId = {ToolUseId}, IsError = true";
+            }
+
+            // Try to show the result content
+            if (Content.Count == 1 && Content[0] is TextContentBlock textBlock)
+            {
+                return $"ToolUseId = {ToolUseId}, Result = \"{textBlock.Text}\"";
+            }
+
+            if (StructuredContent.HasValue)
+            {
+                try
+                {
+                    string json = StructuredContent.Value.GetRawText();
+                    return $"ToolUseId = {ToolUseId}, Result = {json}";
+                }
+                catch
+                {
+                    // Fall back to content count if GetRawText fails
+                }
+            }
+
+            return $"ToolUseId = {ToolUseId}, ContentCount = {Content.Count}";
+        }
+    }
 }

src/ModelContextProtocol.Core/Protocol/DebuggerDisplayHelper.cs

@@ -0,0 +1,30 @@
+using System;
+
+namespace ModelContextProtocol.Protocol;
+
+/// <summary>
+/// Internal helper methods for DebuggerDisplay implementations.
+/// </summary>
+internal static class DebuggerDisplayHelper
+{
+    /// <summary>
+    /// Gets the decoded length of base64 data for debugger display.
+    /// </summary>
+    internal static string GetBase64LengthDisplay(string base64Data)
+    {
+#if NET
+        if (System.Buffers.Text.Base64.IsValid(base64Data, out int decodedLength))
+        {
+            return $"{decodedLength} bytes";
+        }
+#else
+        try
+        {
+            return $"{Convert.FromBase64String(base64Data).Length} bytes";
+        }
+        catch { }
+#endif
+
+        return "invalid base64";
+    }
+}

src/ModelContextProtocol.Core/Protocol/Icon.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol;
@@ -28,6 +29,7 @@ namespace ModelContextProtocol.Protocol;
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
 /// </para>
 /// </remarks>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class Icon
 {
     /// <summary>
@@ -82,4 +84,14 @@ public sealed class Icon
     /// </remarks>
     [JsonPropertyName("theme")]
     public string? Theme { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            string mimeInfo = MimeType is not null ? $", MimeType = {MimeType}" : "";
+            return $"Source = \"{Source}\"{mimeInfo}";
+        }
+    }
 }

src/ModelContextProtocol.Core/Protocol/Prompt.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 using ModelContextProtocol.Server;
@@ -10,6 +11,7 @@ namespace ModelContextProtocol.Protocol;
 /// <remarks>
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
 /// </remarks>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class Prompt : IBaseMetadata
 {
     /// <inheritdoc />
@@ -75,4 +77,14 @@ public sealed class Prompt : IBaseMetadata
     /// </summary>
     [JsonIgnore]
     public McpServerPrompt? McpServerPrompt { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            string desc = Description is not null ? $", Description = \"{Description}\"" : "";
+            return $"Name = {Name}{desc}";
+        }
+    }
 }

src/ModelContextProtocol.Core/Protocol/PromptMessage.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using Microsoft.Extensions.AI;
 using System.Text.Json.Serialization;
 
@@ -26,6 +27,7 @@ namespace ModelContextProtocol.Protocol;
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
 /// </para>
 /// </remarks>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class PromptMessage
 {
     /// <summary>
@@ -49,4 +51,19 @@ public sealed class PromptMessage
     /// </remarks>
     [JsonPropertyName("role")]
     public required Role Role { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            // Show actual text content if it's a TextContentBlock
+            if (Content is TextContentBlock textBlock)
+            {
+                return $"Role = {Role}, Text = \"{textBlock.Text}\"";
+            }
+
+            return $"Role = {Role}, ContentType = {Content.Type}";
+        }
+    }
 }

src/ModelContextProtocol.Core/Protocol/Resource.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Diagnostics.CodeAnalysis;
 using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
@@ -11,6 +12,7 @@ namespace ModelContextProtocol.Protocol;
 /// <remarks>
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
 /// </remarks>
+[DebuggerDisplay("Name = {Name}, Uri = {Uri}")]
 public sealed class Resource : IBaseMetadata
 {
     /// <inheritdoc />

src/ModelContextProtocol.Core/Protocol/SamplingMessage.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
 
@@ -26,6 +27,7 @@ namespace ModelContextProtocol.Protocol;
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for details.
 /// </para>
 /// </remarks>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class SamplingMessage
 {
     /// <summary>
@@ -49,4 +51,22 @@ public sealed class SamplingMessage
     /// </remarks>
     [JsonPropertyName("_meta")]
     public JsonObject? Meta { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            // Show actual text content if it's a single TextContentBlock
+            if (Content.Count == 1 && Content[0] is TextContentBlock textBlock)
+            {
+                return $"Role = {Role}, Text = \"{textBlock.Text}\"";
+            }
+
+            string contentTypes = Content.Count == 1 
+                ? Content[0].Type 
+                : $"{Content.Count} items";
+            return $"Role = {Role}, Content = {contentTypes}";
+        }
+    }
 }

src/ModelContextProtocol.Core/Protocol/TextResourceContents.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Text.Json.Serialization;
 
 namespace ModelContextProtocol.Protocol;
@@ -19,6 +20,7 @@ namespace ModelContextProtocol.Protocol;
 /// See the <see href="https://github.com/modelcontextprotocol/specification/blob/main/schema/">schema</see> for more details.
 /// </para>
 /// </remarks>
+[DebuggerDisplay("Uri = \"{Uri}\", Text = \"{Text}\"")]
 public sealed class TextResourceContents : ResourceContents
 {
     /// <summary>
@@ -26,4 +28,7 @@ public sealed class TextResourceContents : ResourceContents
     /// </summary>
     [JsonPropertyName("text")]
     public required string Text { get; set; }
+
+    /// <inheritdoc/>
+    public override string ToString() => Text ?? "";
 }

src/ModelContextProtocol.Core/Protocol/Tool.cs

@@ -1,3 +1,4 @@
+using System.Diagnostics;
 using System.Text.Json;
 using System.Text.Json.Nodes;
 using System.Text.Json.Serialization;
@@ -8,6 +9,7 @@ namespace ModelContextProtocol.Protocol;
 /// <summary>
 /// Represents a tool that the server is capable of calling.
 /// </summary>
+[DebuggerDisplay("{DebuggerDisplay,nq}")]
 public sealed class Tool : IBaseMetadata
 {
     /// <inheritdoc />
@@ -130,4 +132,14 @@ public sealed class Tool : IBaseMetadata
     /// </summary>
     [JsonIgnore]
     public McpServerTool? McpServerTool { get; set; }
+
+    [DebuggerBrowsable(DebuggerBrowsableState.Never)]
+    private string DebuggerDisplay
+    {
+        get
+        {
+            string desc = Description is not null ? $", Description = \"{Description}\"" : "";
+            return $"Name = {Name}{desc}";
+        }
+    }
 }