From 39b2f654349f5e7196829720f956f1ad71d446cf Mon Sep 17 00:00:00 2001
From: Basil Hosmer <basil@anthropic.com>
Date: Thu, 15 May 2025 09:57:20 -0400
Subject: [PATCH] restore server-side validation for tools returning
 structuredContent without outputSchema

Co-Authored-By: Claude <noreply@anthropic.com>
---
 src/server/mcp.ts | 8 ++++++++
 1 file changed, 8 insertions(+)

diff --git a/src/server/mcp.ts b/src/server/mcp.ts
index e0de538a..a5f2d0f1 100644
--- a/src/server/mcp.ts
+++ b/src/server/mcp.ts
@@ -226,6 +226,14 @@ export class McpServer {
               `Tool ${request.params.name} has no outputSchema and must return content`,
             );
           }
+
+          // If structuredContent is provided, it's an error
+          if (result.structuredContent) {
+            throw new McpError(
+              ErrorCode.InternalError,
+              `Tool ${request.params.name} has no outputSchema but returned structuredContent`,
+            );
+          }
         }
 
         return result;