Python: Normalize OpenAI tool-call argument envelopes on parse

python/packages/core/agent_framework/_types.py

@@ -70,6 +70,21 @@ def _parse_content_list(contents_data: Sequence[Any]) -> list[Content]:
     return contents
 
 
+def normalize_function_call_arguments(
+    arguments: str | Mapping[str, Any] | None,
+) -> str | dict[str, Any] | None:
+    """Normalize provider tool-call arguments to a mapping when possible."""
+    if not isinstance(arguments, str):
+        return dict(arguments) if isinstance(arguments, Mapping) else arguments
+
+    try:
+        loaded = json.loads(arguments)
+    except (json.JSONDecodeError, TypeError):
+        return arguments
+
+    return loaded if isinstance(loaded, dict) else arguments
+
+
 # region Internal Helper functions for unified Content
 
 

python/packages/core/agent_framework/openai/_chat_client.py

@@ -49,6 +49,7 @@
     Message,
     ResponseStream,
     UsageDetails,
+    normalize_function_call_arguments,
 )
 from ..exceptions import (
     ChatClientException,
@@ -556,7 +557,7 @@ def _parse_tool_calls_from_openai(self, choice: Choice | ChunkChoice) -> list[Co
                     fcc = Content.from_function_call(
                         call_id=tool.id if tool.id else "",
                         name=tool.function.name if tool.function.name else "",
-                        arguments=tool.function.arguments if tool.function.arguments else "",
+                        arguments=normalize_function_call_arguments(tool.function.arguments if tool.function.arguments else ""),
                         raw_representation=tool.function,
                     )
                     resp.append(fcc)

python/packages/core/agent_framework/openai/_responses_client.py

@@ -73,6 +73,7 @@
     TextSpanRegion,
     UsageDetails,
     detect_media_type_from_base64,
+    normalize_function_call_arguments,
     prepend_instructions_to_messages,
     validate_tool_mode,
 )
@@ -1523,7 +1524,7 @@ def _parse_response_from_openai(
                         Content.from_function_call(
                             call_id=item.call_id,
                             name=item.name,
-                            arguments=item.arguments,
+                            arguments=normalize_function_call_arguments(item.arguments),
                             additional_properties={"fc_id": item.id, "status": item.status},
                             raw_representation=item,
                         )
@@ -1535,7 +1536,7 @@ def _parse_response_from_openai(
                             function_call=Content.from_function_call(
                                 call_id=item.id,
                                 name=item.name,
-                                arguments=item.arguments,
+                                arguments=normalize_function_call_arguments(item.arguments),
                                 additional_properties={"server_label": item.server_label},
                                 raw_representation=item,
                             ),
@@ -1915,7 +1916,7 @@ def _parse_chunk_from_openai(
                                 function_call=Content.from_function_call(
                                     call_id=event_item.id,
                                     name=event_item.name,
-                                    arguments=event_item.arguments,
+                                    arguments=normalize_function_call_arguments(event_item.arguments),
                                     additional_properties={"server_label": event_item.server_label},
                                     raw_representation=event_item,
                                 ),

python/packages/core/tests/openai/test_openai_chat_client.py

@@ -862,6 +862,32 @@ def test_function_approval_content_is_skipped_in_preparation(
     assert prepared_mixed[0]["content"] == "I need approval for this action."
 
 
+def test_parse_tool_calls_from_openai_normalizes_json_object_arguments(
+    openai_unit_test_env: dict[str, str],
+) -> None:
+    client = OpenAIChatClient()
+
+    mock_tool_function = MagicMock()
+    mock_tool_function.name = "get_weather"
+    mock_tool_function.arguments = '{"city": "Seattle"}'
+
+    mock_tool = MagicMock()
+    mock_tool.id = "call_123"
+    mock_tool.function = mock_tool_function
+
+    mock_message = MagicMock()
+    mock_message.tool_calls = [mock_tool]
+
+    mock_choice = MagicMock()
+    mock_choice.delta = mock_message
+
+    contents = client._parse_tool_calls_from_openai(mock_choice)
+
+    assert len(contents) == 1
+    assert contents[0].type == "function_call"
+    assert contents[0].arguments == {"city": "Seattle"}
+
+
 def test_usage_content_in_streaming_response(
     openai_unit_test_env: dict[str, str],
 ) -> None:

python/packages/core/tests/openai/test_openai_responses_client.py

@@ -1037,7 +1037,7 @@ def test_response_content_creation_with_function_call() -> None:
     function_call = response.messages[0].contents[0]
     assert function_call.call_id == "call_123"
     assert function_call.name == "get_weather"
-    assert function_call.arguments == '{"location": "Seattle"}'
+    assert function_call.arguments == {"location": "Seattle"}
 
 
 def test_prepare_content_for_opentool_approval_response() -> None:
@@ -3581,7 +3581,7 @@ def test_parse_response_from_openai_function_call_includes_status() -> None:
     assert function_call.type == "function_call"
     assert function_call.call_id == "call_123"
     assert function_call.name == "get_weather"
-    assert function_call.arguments == '{"location": "Seattle"}'
+    assert function_call.arguments == {"location": "Seattle"}
     # Verify status is included in additional_properties
     assert function_call.additional_properties is not None
     assert function_call.additional_properties.get("status") == "completed"