Address review feedback: use newline separator, IsNullOrWhiteSpace, and 'is not' pattern

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

Author: Copilot

src/ModelContextProtocol.Core/Server/AIFunctionMcpServerTool.cs

@@ -427,18 +427,18 @@ private static void ValidateToolName(string name)
         // When structured content is disabled, try to extract the return description from ReturnJsonSchema
         // and append it to the tool description so the information is available to consumers
         string? returnDescription = GetReturnDescription(function.ReturnJsonSchema);
-        if (returnDescription is null)
+        if (string.IsNullOrWhiteSpace(returnDescription))
         {
             return description;
         }
 
         // Synthesize a combined description
-        if (string.IsNullOrEmpty(description))
+        if (string.IsNullOrWhiteSpace(description))
         {
             return $"Returns: {returnDescription}";
         }
 
-        return $"{description} Returns: {returnDescription}";
+        return $"{description}\nReturns: {returnDescription}";
     }
 
     /// <summary>
@@ -447,9 +447,9 @@ private static void ValidateToolName(string name)
     private static string? GetReturnDescription(JsonElement? returnJsonSchema)
     {
         if (returnJsonSchema is not JsonElement schema ||
-            schema.ValueKind != JsonValueKind.Object ||
+            schema.ValueKind is not JsonValueKind.Object ||
             !schema.TryGetProperty("description", out JsonElement descriptionElement) ||
-            descriptionElement.ValueKind != JsonValueKind.String)
+            descriptionElement.ValueKind is not JsonValueKind.String)
         {
             return null;
         }

tests/ModelContextProtocol.Tests/Server/McpServerToolTests.cs

@@ -750,7 +750,7 @@ public void ReturnDescription_StructuredOutputDisabled_IncludedInToolDescription
         // When UseStructuredContent is false (default), return description should be appended to tool description
         McpServerTool tool = McpServerTool.Create(ToolWithReturnDescription);
 
-        Assert.Equal("Tool that returns data. Returns: The computed result", tool.ProtocolTool.Description);
+        Assert.Equal("Tool that returns data.\nReturns: The computed result", tool.ProtocolTool.Description);
         Assert.Null(tool.ProtocolTool.OutputSchema);
     }
 
@@ -786,7 +786,7 @@ public void ReturnDescription_ExplicitDescriptionOption_SynthesizesWithReturnDes
         // the return description should be appended since UseStructuredContent is false
         McpServerTool tool = McpServerTool.Create(ToolWithReturnDescription, new() { Description = "Custom description" });
 
-        Assert.Equal("Custom description Returns: The computed result", tool.ProtocolTool.Description);
+        Assert.Equal("Custom description\nReturns: The computed result", tool.ProtocolTool.Description);
         Assert.Null(tool.ProtocolTool.OutputSchema);
     }