diff --git a/src/pyr/ai/client.py b/src/pyr/ai/client.py
index 1757e69..1a261a3 100644
--- a/src/pyr/ai/client.py
+++ b/src/pyr/ai/client.py
@@ -15,12 +15,14 @@ logger = logging.getLogger(__name__)
 class Message(BaseModel):
     role: str
     content: str
+    tool_calls: Optional[List[Dict[str, Any]]] = None  # Added for OpenAI tool calls
+    tool_call_id: Optional[str] = None  # Added for tool responses
 
 
 class ToolCall(BaseModel):
     id: str
     type: str
-    function: Dict[str, Any]
+    function: Dict[str, Any] = None
 
 
 class AIResponse(BaseModel):
@@ -47,13 +49,15 @@ class BaseAIClient(ABC):
     async def add_user_message(self, content: str) -> None:
         self.messages.append(Message(role="user", content=content))
     
-    async def add_assistant_message(self, content: str) -> None:
-        self.messages.append(Message(role="assistant", content=content))
+    async def add_assistant_message(self, content: str, tool_calls: Optional[List[Dict[str, Any]]] = None) -> None:
+        self.messages.append(Message(role="assistant", content=content, tool_calls=tool_calls))
     
     async def add_tool_result(self, tool_call_id: str, result: str) -> None:
+        # OpenAI expects tool results in a specific format
         self.messages.append(Message(
             role="tool",
-            content=json.dumps({"tool_call_id": tool_call_id, "result": result})
+            content=result,
+            tool_call_id=tool_call_id
         ))
     
     @abstractmethod
@@ -78,13 +82,27 @@ class OpenAIClient(BaseAIClient):
         self.base_url = config.get_completions_url()
         self.headers = config.get_auth_headers()
     
+    def _prepare_message_for_api(self, msg: Message) -> Dict[str, Any]:
+        """Convert internal Message to OpenAI API format"""
+        api_msg = {"role": msg.role, "content": msg.content}
+        
+        # Add tool_calls if present (for assistant messages)
+        if msg.tool_calls:
+            api_msg["tool_calls"] = msg.tool_calls
+        
+        # Add tool_call_id if present (for tool messages)
+        if msg.tool_call_id:
+            api_msg["tool_call_id"] = msg.tool_call_id
+        
+        return api_msg
+    
     async def chat(self, role: str, message: str) -> str:
         if message:
             await self.add_user_message(message)
         
         payload = {
             "model": self.config.model,
-            "messages": [msg.dict() for msg in self.messages],
+            "messages": [self._prepare_message_for_api(msg) for msg in self.messages],
             "temperature": self.config.temperature,
         }
         
@@ -110,21 +128,27 @@ class OpenAIClient(BaseAIClient):
             raise
     
     async def chat_with_tools(self, role: str, message: str, tools: List[Dict[str, Any]]) -> AIResponse:
+        # Add message only if it's not empty
         if message:
             await self.add_user_message(message)
         
+        # If no messages, return empty response
+        if not self.messages:
+            return AIResponse(content="", tool_calls=None, usage=None)
+
         payload = {
             "model": self.config.model,
-            "messages": [msg.dict() for msg in self.messages],
+            "messages": [self._prepare_message_for_api(msg) for msg in self.messages],
             "temperature": self.config.temperature,
         }
-        
+
         if tools:
             payload["tools"] = tools
-        
+            payload["tool_choice"] = "auto"  # Let the model decide when to use tools
+
         if self.config.max_tokens:
             payload["max_tokens"] = self.config.max_tokens
-        
+
         try:
             response = await self.client.post(
                 self.base_url,
@@ -132,32 +156,35 @@ class OpenAIClient(BaseAIClient):
                 json=payload
             )
             response.raise_for_status()
-            
+
             data = response.json()
             choice = data["choices"][0]
             message_data = choice["message"]
-            
+
             tool_calls = None
+            tool_calls_raw = None
             if "tool_calls" in message_data and message_data["tool_calls"]:
+                tool_calls_raw = message_data["tool_calls"]
                 tool_calls = [
                     ToolCall(
                         id=tc["id"],
                         type=tc["type"],
                         function=tc["function"]
-                    ) for tc in message_data["tool_calls"]
+                    ) for tc in tool_calls_raw
                 ]
+
+            # Content can be None when only tool calls are returned
+            content = message_data.get("content") or ""
             
-            content = message_data.get("content", "")
-            
-            if content:
-                await self.add_assistant_message(content)
-            
+            # Add the assistant's response to history, including tool calls if present
+            await self.add_assistant_message(content, tool_calls_raw)
+
             return AIResponse(
                 content=content,
                 tool_calls=tool_calls,
                 usage=data.get("usage")
             )
-            
+
         except Exception as e:
             logger.error(f"OpenAI API error: {e}")
             raise
@@ -168,7 +195,7 @@ class OpenAIClient(BaseAIClient):
         
         payload = {
             "model": self.config.model,
-            "messages": [msg.dict() for msg in self.messages],
+            "messages": [self._prepare_message_for_api(msg) for msg in self.messages],
             "temperature": self.config.temperature,
             "stream": True,
         }
diff --git a/src/pyr/core/app.py b/src/pyr/core/app.py
index 422df76..b0493ef 100644
--- a/src/pyr/core/app.py
+++ b/src/pyr/core/app.py
@@ -277,8 +277,8 @@ class PyrApp:
             for tool_call in response.tool_calls:
                 try:
                     result = await self.tool_registry.execute_tool(
-                        tool_call.function.name,
-                        tool_call.function.arguments
+                        tool_call.function['name'],
+                        tool_call.function['arguments']
                     )
                     # Send tool result back to AI
                     await self.ai_client.add_tool_result(tool_call.id, result)