diff --git a/aisuite/utils/tools.py b/aisuite/utils/tools.py
index 11b4bd57..ff6e5d18 100644
--- a/aisuite/utils/tools.py
+++ b/aisuite/utils/tools.py
@@ -1,3 +1,5 @@
+import dataclasses
+import datetime
 from typing import Callable, Dict, Any, Type, Optional
 from pydantic import BaseModel, create_model, Field, ValidationError
 import inspect
@@ -275,7 +277,7 @@ def execute_tool(self, tool_calls) -> tuple[list, list]:
                     {
                         "role": "tool",
                         "name": tool_name,
-                        "content": json.dumps(result),
+                        "content": json.dumps(result, cls=DefaultJSONEncoder),
                         "tool_call_id": tool_call_id,
                     }
                 )
@@ -283,3 +285,30 @@ def execute_tool(self, tool_calls) -> tuple[list, list]:
                 raise ValueError(f"Error in tool '{tool_name}' parameters: {e}")
 
         return results, messages
+
+
+class DefaultJSONEncoder(json.JSONEncoder):
+    """
+    Based on Flask https://flask.palletsprojects.com/en/stable/api/#flask.json.provider.DefaultJSONProvider
+    Provide JSON operations using Python’s built-in json library. Serializes the following additional data types:
+
+    dataclasses: by calling `asdict`
+    datetime.dateime: by calling `datetime.datetime.isoformat()`
+    Markup and other objects: by checking for a __html__ method to return a str.
+    """
+
+    def default(self, obj: Any) -> Any:
+        # Handle dataclasses by converting them to dictionaries
+        if dataclasses.is_dataclass(obj):
+            return dataclasses.asdict(obj)
+
+        # Handle datetime objects by using isoformat
+        if isinstance(obj, datetime.datetime):
+            return obj.isoformat()
+
+        # Check for __html__ method which is used by Markupsafe a ton of other libraries and call it
+        if hasattr(obj, "__html__") and callable(getattr(obj, "__html__")):
+            return obj.__html__()
+
+        # Let the base class handle anything else
+        return super().default(obj)
diff --git a/tests/utils/test_tool_manager.py b/tests/utils/test_tool_manager.py
index c78e6999..abb3a975 100644
--- a/tests/utils/test_tool_manager.py
+++ b/tests/utils/test_tool_manager.py
@@ -3,6 +3,9 @@
 from typing import Dict
 from aisuite.utils.tools import Tools  # Import your ToolManager class
 from enum import Enum
+import dataclasses
+from datetime import datetime
+from markupsafe import Markup
 
 
 # Define a sample tool function and Pydantic model for testing
@@ -21,6 +24,19 @@ class TemperatureParams(BaseModel):
     unit: str = "Celsius"
 
 
+@dataclasses.dataclass
+class WeatherReport:
+    temperature: int
+    temperature_unit: TemperatureUnit = TemperatureUnit.CELSIUS
+    last_forecast_datetime: datetime = datetime(2024, 1, 1, 11, 5, 5)
+    forecast: Markup = Markup(
+        """
+    <h1>Weather Report for Today</h1>
+    <section>It's looking really good.</section>
+    """
+    )
+
+
 def get_current_temperature(location: str, unit: str = "Celsius") -> Dict[str, str]:
     """Gets the current temperature for a specific location and unit."""
     return {"location": location, "unit": unit, "temperature": "72"}
@@ -38,6 +54,18 @@ def get_current_temperature_v2(
     return {"location": location, "unit": unit, "temperature": "72"}
 
 
+class WeatherReportParams(BaseModel):
+    location: str
+
+
+def get_weather_report_complex_type(location: str) -> WeatherReport:
+    """Gets a detailed weather report for a location"""
+    return WeatherReport(
+        20,
+        TemperatureUnit.CELSIUS,
+    )
+
+
 class TestToolManager(unittest.TestCase):
     def setUp(self):
         self.tool_manager = Tools()
@@ -195,6 +223,35 @@ def test_add_tool_with_enum(self):
             tools == expected_tool_spec
         ), f"Expected {expected_tool_spec}, but got {tools}"
 
+    def test_execute_tool_with_complex_type(self):
+        """Test executing a registered tool with valid parameters."""
+        self.tool_manager._add_tool(
+            get_weather_report_complex_type, WeatherReportParams
+        )
+        tool_call = {
+            "id": "call_1",
+            "function": {
+                "name": "get_weather_report_complex_type",
+                "arguments": {"location": "San Francisco"},
+            },
+        }
+        result, result_message = self.tool_manager.execute_tool(tool_call)
+
+        # Assuming result is returned as a list with a single dictionary
+        result_obj = result[0] if isinstance(result, list) else result
+        self.assertIsInstance(result_obj, WeatherReport)
+
+        # Check that the result matches expected output
+        self.assertEqual(
+            result_obj.forecast,
+            Markup(
+                "\n    <h1>Weather Report for Today</h1>\n    <section>It's looking really good.</section>\n    "
+            ),
+        )
+        self.assertEqual(
+            result_obj.last_forecast_datetime, datetime(2024, 1, 1, 11, 5, 5)
+        )
+
 
 if __name__ == "__main__":
     unittest.main()