fix: Propagate MCP tools output schema to FunctionDeclaration

PiperOrigin-RevId: 825380145

src/google/adk/tools/mcp_tool/mcp_tool.py

@@ -119,10 +119,15 @@ class McpTool(BaseAuthenticatedTool):
     Returns:
         FunctionDeclaration: The Gemini function declaration for the tool.
     """
-    schema_dict = self._mcp_tool.inputSchema
-    parameters = _to_gemini_schema(schema_dict)
+    input_schema = self._mcp_tool.inputSchema
+    parameters = _to_gemini_schema(input_schema)
+    output_schema = self._mcp_tool.outputSchema
+    response = _to_gemini_schema(output_schema)
     function_decl = FunctionDeclaration(
-        name=self.name, description=self.description, parameters=parameters
+        name=self.name,
+        description=self.description,
+        parameters=parameters,
+        response=response,
     )
     return function_decl
 

tests/unittests/tools/mcp_tool/test_mcp_tool.py

@@ -36,6 +36,7 @@ try:
   from google.adk.tools.mcp_tool.mcp_tool import MCPTool
   from google.adk.tools.tool_context import ToolContext
   from google.genai.types import FunctionDeclaration
+  from google.genai.types import Type
   from mcp.types import CallToolResult
   from mcp.types import TextContent
 except ImportError as e:
@@ -49,6 +50,7 @@ except ImportError as e:
     MCPTool = DummyClass
     ToolContext = DummyClass
     FunctionDeclaration = DummyClass
+    Type = DummyClass
     CallToolResult = DummyClass
     TextContent = DummyClass
   else:
@@ -70,6 +72,7 @@ class MockMCPTool:
         },
         "required": ["param1"],
     }
+    self.outputSchema = None
 
 
 class TestMCPTool:
@@ -145,6 +148,49 @@ class TestMCPTool:
     assert declaration.name == "test_tool"
     assert declaration.description == "Test tool description"
     assert declaration.parameters is not None
+    assert declaration.response is None
+
+  def test_get_declaration_with_output_schema(self):
+    """Test function declaration generation with an output schema."""
+    self.mock_mcp_tool.outputSchema = {
+        "type": "object",
+        "properties": {
+            "status": {
+                "type": "string",
+                "description": "The status of the operation",
+            },
+        },
+    }
+    tool = MCPTool(
+        mcp_tool=self.mock_mcp_tool,
+        mcp_session_manager=self.mock_session_manager,
+    )
+
+    declaration = tool._get_declaration()
+
+    assert isinstance(declaration, FunctionDeclaration)
+    assert declaration.response is not None
+    assert declaration.response.type == Type.OBJECT
+    assert "status" in declaration.response.properties
+    assert declaration.response.properties["status"].type == Type.STRING
+    assert (
+        declaration.response.properties["status"].description
+        == "The status of the operation"
+    )
+
+  def test_get_declaration_with_empty_output_schema(self):
+    """Test function declaration with an empty output schema."""
+    self.mock_mcp_tool.outputSchema = {}
+    tool = MCPTool(
+        mcp_tool=self.mock_mcp_tool,
+        mcp_session_manager=self.mock_session_manager,
+    )
+
+    declaration = tool._get_declaration()
+
+    assert declaration.response is not None
+    assert declaration.response.type == Type.OBJECT
+    assert declaration.response.properties is None
 
   @pytest.mark.asyncio
   async def test_run_async_impl_no_auth(self):