small fixes

src/server/mcp.test.ts

@@ -1203,72 +1203,68 @@ describe("tool()", () => {
       }),
     ).rejects.toThrow(/Tool test has an output schema but no structured content was provided/);
   });
-
-    /***
+  /***
    * Test: Tool with Output Schema Must Provide Structured Content
    */
-    test("should not throw error when tool with outputSchema returns no structuredContent and isError is true", async () => {
-      const mcpServer = new McpServer({
-        name: "test server",
-        version: "1.0",
-      });
-  
-      const client = new Client({
-        name: "test client",
-        version: "1.0",
-      });
-  
-      // Register a tool with outputSchema that returns only content without structuredContent
-      mcpServer.registerTool(
-        "test",
-        {
-          description: "Test tool with output schema but missing structured content",
-          inputSchema: {
-            input: z.string(),
-          },
-          outputSchema: {
-            processedInput: z.string(),
-            resultType: z.string(),
-          },
+  test("should skip outputSchema validation when isError is true", async () => {
+    const mcpServer = new McpServer({
+      name: "test server",
+      version: "1.0",
+    });
+
+    const client = new Client({
+      name: "test client",
+      version: "1.0",
+    });
+
+    mcpServer.registerTool(
+      "test",
+      {
+        description: "Test tool with output schema but missing structured content",
+        inputSchema: {
+          input: z.string(),
         },
-        async ({ input }) => ({
-          // Only return content without structuredContent
-          content: [
-            {
-              type: "text",
-              text: `Processed: ${input}`,
-            },
-          ],
-          isError: true,
-        })
-      );
-  
-      const [clientTransport, serverTransport] =
-        InMemoryTransport.createLinkedPair();
-  
-      await Promise.all([
-        client.connect(clientTransport),
-        mcpServer.server.connect(serverTransport),
-      ]);
-  
-      // Call the tool and expect it to not throw an error
-      await expect(
-        client.callTool({
-          name: "test",
-          arguments: {
-            input: "hello",
-          },
-        }),
-      ).resolves.toStrictEqual({
+        outputSchema: {
+          processedInput: z.string(),
+          resultType: z.string(),
+        },
+      },
+      async ({ input }) => ({
         content: [
           {
             type: "text",
-            text: `Processed: hello`,
+            text: `Processed: ${input}`,
           },
         ],
         isError: true,
-      });
+      })
+    );
+
+    const [clientTransport, serverTransport] =
+      InMemoryTransport.createLinkedPair();
+
+    await Promise.all([
+      client.connect(clientTransport),
+      mcpServer.server.connect(serverTransport),
+    ]);
+
+    await expect(
+      client.callTool({
+        name: "test",
+        arguments: {
+          input: "hello",
+        },
+      }),
+    ).resolves.toStrictEqual({
+      content: [
+        {
+          type: "text",
+          text: `Processed: hello`,
+        },
+      ],
+      isError: true,
     });
+  });
 
   /***
    * Test: Schema Validation Failure for Invalid Structured Content

src/server/mcp.ts

@@ -200,7 +200,7 @@ export class McpServer {
           }
         }
 
-        if (tool.outputSchema && (result.isError !== true)) {
+        if (tool.outputSchema && !result.isError) {
           if (!result.structuredContent) {
             throw new McpError(
               ErrorCode.InvalidParams,