diff --git a/src/Schema/Result/CallToolResult.php b/src/Schema/Result/CallToolResult.php
index 8a01bbb2..da3be4f6 100644
--- a/src/Schema/Result/CallToolResult.php
+++ b/src/Schema/Result/CallToolResult.php
@@ -38,12 +38,14 @@ class CallToolResult implements ResultInterface
     /**
      * Create a new CallToolResult.
      *
-     * @param Content[] $content The content of the tool result
-     * @param bool      $isError Whether the tool execution resulted in an error.  If not set, this is assumed to be false (the call was successful).
+     * @param Content[] $content           The content of the tool result
+     * @param bool      $isError           Whether the tool execution resulted in an error.  If not set, this is assumed to be false (the call was successful).
+     * @param mixed[]   $structuredContent JSON content for `structuredContent`
      */
     public function __construct(
         public readonly array $content,
         public readonly bool $isError = false,
+        public readonly ?array $structuredContent = null,
     ) {
         foreach ($this->content as $item) {
             if (!$item instanceof Content) {
@@ -107,9 +109,15 @@ public static function fromArray(array $data): self
      */
     public function jsonSerialize(): array
     {
-        return [
+        $result = [
             'content' => $this->content,
             'isError' => $this->isError,
         ];
+
+        if ($this->structuredContent) {
+            $result['structuredContent'] = $this->structuredContent;
+        }
+
+        return $result;
     }
 }
diff --git a/src/Server/Handler/Request/CallToolHandler.php b/src/Server/Handler/Request/CallToolHandler.php
index dea2725b..c1f10b9d 100644
--- a/src/Server/Handler/Request/CallToolHandler.php
+++ b/src/Server/Handler/Request/CallToolHandler.php
@@ -59,14 +59,17 @@ public function handle(Request $request, SessionInterface $session): Response|Er
             }
 
             $result = $this->referenceHandler->handle($reference, $arguments);
-            $formatted = $reference->formatResult($result);
+
+            if (!$result instanceof CallToolResult) {
+                $result = new CallToolResult($reference->formatResult($result));
+            }
 
             $this->logger->debug('Tool executed successfully', [
                 'name' => $toolName,
                 'result_type' => \gettype($result),
             ]);
 
-            return new Response($request->getId(), new CallToolResult($formatted));
+            return new Response($request->getId(), $result);
         } catch (ToolNotFoundException $e) {
             $this->logger->error('Tool not found', ['name' => $toolName]);
 
diff --git a/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php b/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
index 4423cbd6..11b799bf 100644
--- a/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
+++ b/tests/Unit/Server/Handler/Request/CallToolHandlerTest.php
@@ -342,6 +342,64 @@ public function testHandleWithSpecialCharactersInArguments(): void
         $this->assertEquals($expectedResult, $response->result);
     }
 
+    public function testHandleReturnsStructuredContentResult(): void
+    {
+        $request = $this->createCallToolRequest('structured_tool', ['query' => 'php']);
+        $toolReference = $this->createMock(ToolReference::class);
+        $structuredResult = new CallToolResult([new TextContent('Rendered results')], false, ['result' => 'Rendered results']);
+
+        $this->referenceProvider
+            ->expects($this->once())
+            ->method('getTool')
+            ->with('structured_tool')
+            ->willReturn($toolReference);
+
+        $this->referenceHandler
+            ->expects($this->once())
+            ->method('handle')
+            ->with($toolReference, ['query' => 'php'])
+            ->willReturn($structuredResult);
+
+        $toolReference
+            ->expects($this->never())
+            ->method('formatResult');
+
+        $response = $this->handler->handle($request, $this->session);
+
+        $this->assertInstanceOf(Response::class, $response);
+        $this->assertSame($structuredResult, $response->result);
+        $this->assertEquals(['result' => 'Rendered results'], $response->result->jsonSerialize()['structuredContent'] ?? []);
+    }
+
+    public function testHandleReturnsCallToolResult(): void
+    {
+        $request = $this->createCallToolRequest('result_tool', ['query' => 'php']);
+        $toolReference = $this->createMock(ToolReference::class);
+        $callToolResult = new CallToolResult([new TextContent('Error result')], true);
+
+        $this->referenceProvider
+            ->expects($this->once())
+            ->method('getTool')
+            ->with('result_tool')
+            ->willReturn($toolReference);
+
+        $this->referenceHandler
+            ->expects($this->once())
+            ->method('handle')
+            ->with($toolReference, ['query' => 'php'])
+            ->willReturn($callToolResult);
+
+        $toolReference
+            ->expects($this->never())
+            ->method('formatResult');
+
+        $response = $this->handler->handle($request, $this->session);
+
+        $this->assertInstanceOf(Response::class, $response);
+        $this->assertSame($callToolResult, $response->result);
+        $this->assertArrayNotHasKey('structuredContent', $response->result->jsonSerialize());
+    }
+
     /**
      * @param array<string, mixed> $arguments
      */