Fix Agent.kickoff() to pass custom system_template and prompt_template to LiteAgent

- Add system_template and prompt_template fields to LiteAgent class
- Update LiteAgent._get_default_system_prompt() to use custom templates when provided
- Pass template parameters from Agent.kickoff() and Agent.kickoff_async() to LiteAgent
- Add comprehensive tests to verify custom templates are passed and used correctly
- Maintain backward compatibility with default behavior when no templates provided

Fixes #3261

Co-Authored-By: João <joao@crewai.com>

src/crewai/agent.py

@@ -817,6 +817,8 @@ class Agent(BaseAgent):
             original_agent=self,
             guardrail=self.guardrail,
             guardrail_max_retries=self.guardrail_max_retries,
+            system_template=self.system_template,
+            prompt_template=self.prompt_template,
         )
 
         return lite_agent.kickoff(messages)
@@ -853,6 +855,8 @@ class Agent(BaseAgent):
             response_format=response_format,
             i18n=self.i18n,
             original_agent=self,
+            system_template=self.system_template,
+            prompt_template=self.prompt_template,
         )
 
         return await lite_agent.kickoff_async(messages)

src/crewai/lite_agent.py

@@ -174,6 +174,14 @@ class LiteAgent(FlowTrackable, BaseModel):
         default=[], description="Callbacks to be used for the agent"
     )
 
+    # Template Properties
+    system_template: Optional[str] = Field(
+        default=None, description="Custom system template for the agent"
+    )
+    prompt_template: Optional[str] = Field(
+        default=None, description="Custom prompt template for the agent"
+    )
+
     # Guardrail Properties
     guardrail: Optional[Union[Callable[[LiteAgentOutput], Tuple[bool, Any]], str]] = (
         Field(
@@ -446,6 +454,26 @@ class LiteAgent(FlowTrackable, BaseModel):
 
     def _get_default_system_prompt(self) -> str:
         """Get the default system prompt for the agent."""
+        if self.system_template and self.prompt_template:
+            system_components = ["role_playing"]
+            if self._parsed_tools:
+                system_components.append("tools")
+            else:
+                system_components.append("no_tools")
+            
+            system_parts = [self.i18n.slice(component) for component in system_components]
+            system_content = "".join(system_parts)
+            
+            system_prompt = self.system_template.replace("{{ .System }}", system_content)
+            
+            system_prompt = (
+                system_prompt.replace("{goal}", self.goal)
+                .replace("{role}", self.role)
+                .replace("{backstory}", self.backstory)
+            )
+            
+            return system_prompt
+        
         base_prompt = ""
         if self._parsed_tools:
             # Use the prompt template for agents with tools
@@ -622,4 +650,4 @@ class LiteAgent(FlowTrackable, BaseModel):
 
     def _append_message(self, text: str, role: str = "assistant") -> None:
         """Append a message to the message list with the given role."""
-        self._messages.append(format_message_for_llm(text, role=role))
+        self._messages.append(format_message_for_llm(text, role=role))

tests/test_lite_agent.py

@@ -118,6 +118,8 @@ def test_lite_agent_created_with_correct_parameters(monkeypatch, verbose):
     assert created_lite_agent["max_iterations"] == max_iter
     assert created_lite_agent["max_execution_time"] == max_execution_time
     assert created_lite_agent["verbose"] == verbose
+    assert created_lite_agent["system_template"] is None
+    assert created_lite_agent["prompt_template"] is None
     assert created_lite_agent["response_format"] is None
 
     # Test with a response_format
@@ -492,4 +494,129 @@ def test_lite_agent_with_invalid_llm():
                 backstory="Test backstory",
                 llm="invalid-model"
             )
-        assert "Expected LLM instance of type BaseLLM" in str(exc_info.value)
+        assert "Expected LLM instance of type BaseLLM" in str(exc_info.value)
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])
+def test_agent_kickoff_with_custom_templates(monkeypatch):
+    """Test that Agent.kickoff() passes custom templates to LiteAgent and they are used correctly."""
+    custom_system_template = """<|start_header_id|>system<|end_header_id|>
+
+{{ .System }}<|eot_id|>"""
+    
+    custom_prompt_template = """<|start_header_id|>user<|end_header_id|>
+
+{{ .Prompt }}<|eot_id|>"""
+    
+    agent = Agent(
+        role="Test Agent",
+        goal="Test Goal", 
+        backstory="Test Backstory",
+        system_template=custom_system_template,
+        prompt_template=custom_prompt_template,
+        llm=LLM(model="gpt-4o-mini"),
+    )
+    
+    created_lite_agent = None
+    original_lite_agent = LiteAgent
+    
+    class MockLiteAgent(original_lite_agent):
+        def __init__(self, **kwargs):
+            nonlocal created_lite_agent
+            created_lite_agent = kwargs
+            super().__init__(**kwargs)
+            
+        def kickoff(self, messages):
+            return LiteAgentOutput(
+                raw="Test response",
+                agent_role=self.role
+            )
+    
+    monkeypatch.setattr("crewai.agent.LiteAgent", MockLiteAgent)
+    
+    result = agent.kickoff("Test query")
+    
+    assert created_lite_agent is not None
+    assert created_lite_agent["system_template"] == custom_system_template
+    assert created_lite_agent["prompt_template"] == custom_prompt_template
+    
+    assert isinstance(result, LiteAgentOutput)
+    assert result.raw == "Test response"
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])  
+def test_agent_kickoff_without_custom_templates(monkeypatch):
+    """Test that Agent.kickoff() works normally when no custom templates are provided."""
+    agent = Agent(
+        role="Test Agent",
+        goal="Test Goal",
+        backstory="Test Backstory", 
+        llm=LLM(model="gpt-4o-mini"),
+    )
+    
+    created_lite_agent = None
+    original_lite_agent = LiteAgent
+    
+    class MockLiteAgent(original_lite_agent):
+        def __init__(self, **kwargs):
+            nonlocal created_lite_agent
+            created_lite_agent = kwargs
+            super().__init__(**kwargs)
+            
+        def kickoff(self, messages):
+            return LiteAgentOutput(
+                raw="Test response",
+                agent_role=self.role
+            )
+    
+    monkeypatch.setattr("crewai.agent.LiteAgent", MockLiteAgent)
+    
+    result = agent.kickoff("Test query")
+    
+    assert created_lite_agent is not None
+    assert created_lite_agent["system_template"] is None
+    assert created_lite_agent["prompt_template"] is None
+    
+    assert isinstance(result, LiteAgentOutput)
+    assert result.raw == "Test response"
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])
+def test_lite_agent_uses_custom_templates_in_system_prompt():
+    """Test that LiteAgent actually uses custom templates when building system prompts."""
+    custom_system_template = "CUSTOM SYSTEM: {{ .System }}"
+    custom_prompt_template = "CUSTOM PROMPT: {{ .Prompt }}"
+    
+    lite_agent = LiteAgent(
+        role="Research Assistant",
+        goal="Help users find accurate information",
+        backstory="You are a helpful research assistant",
+        system_template=custom_system_template,
+        prompt_template=custom_prompt_template,
+        llm=LLM(model="gpt-4o-mini"),
+    )
+    
+    system_prompt = lite_agent._get_default_system_prompt()
+    
+    assert "CUSTOM SYSTEM:" in system_prompt
+    assert "Research Assistant" in system_prompt
+    assert "Help users find accurate information" in system_prompt
+    assert "You are a helpful research assistant" in system_prompt
+
+
+@pytest.mark.vcr(filter_headers=["authorization"])
+def test_lite_agent_falls_back_to_default_without_templates():
+    """Test that LiteAgent falls back to default behavior when no custom templates are provided."""
+    lite_agent = LiteAgent(
+        role="Research Assistant",
+        goal="Help users find accurate information",
+        backstory="You are a helpful research assistant",
+        llm=LLM(model="gpt-4o-mini"),
+    )
+    
+    system_prompt = lite_agent._get_default_system_prompt()
+    
+    assert "CUSTOM SYSTEM:" not in system_prompt
+    assert "Research Assistant" in system_prompt
+    assert "Help users find accurate information" in system_prompt
+    assert "You are a helpful research assistant" in system_prompt