Update docstring and warning message

Author: sjrl

haystack/components/agents/agent.py

@@ -30,6 +30,9 @@ class Agent:
     The component processes messages and executes tools until a exit_condition condition is met.
     The exit_condition can be triggered either by a direct text response or by invoking a specific designated tool.
 
+    When you call an Agent without any tools it acts like a ChatGenerator. It will exit after generating a text
+    response.
+
     ### Usage example
     ```python
     from haystack.components.agents import Agent
@@ -132,7 +135,10 @@ def __init__(
         if self.tools:
             self._tool_invoker = ToolInvoker(tools=self.tools, raise_on_failure=self.raise_on_tool_invocation_failure)
         else:
-            logger.warning("No tools provided to the Agent. It will only return text responses.")
+            logger.warning(
+                "No tools provided to the Agent. The Agent will behave like a ChatGenerator and only return text "
+                "responses. To enable tool usage, pass tools directly to the Agent, not to the chat_generator."
+            )
             self._tool_invoker = None
         self._is_warmed_up = False
 
@@ -304,8 +310,8 @@ async def run_async(
 
             state.set("messages", llm_messages)
 
-            # 2. Check if any of the LLM responses contain a tool call
-            if not any(msg.tool_call for msg in llm_messages):
+            # 2. Check if any of the LLM responses contain a tool call or if the LLM is not using tools
+            if not any(msg.tool_call for msg in llm_messages) or self._tool_invoker is None:
                 return {**state.data}
 
             # 3. Call the ToolInvoker

test/components/agents/test_agent.py

@@ -491,15 +491,17 @@ def test_exit_conditions_checked_across_all_llm_messages(self, monkeypatch, weat
             == "{'weather': 'mostly sunny', 'temperature': 7, 'unit': 'celsius'}"
         )
 
-    def test_agent_with_no_tools(self, monkeypatch):
+    def test_agent_with_no_tools(self, monkeypatch, caplog):
         monkeypatch.setenv("OPENAI_API_KEY", "fake-key")
         generator = OpenAIChatGenerator()
 
         # Mock messages where the exit condition appears in the second message
         mock_messages = [ChatMessage.from_assistant("Berlin")]
 
-        agent = Agent(chat_generator=generator, tools=[], max_agent_steps=3)
-        agent.warm_up()
+        with caplog.at_level("WARNING"):
+            agent = Agent(chat_generator=generator, tools=[], max_agent_steps=3)
+            agent.warm_up()
+            assert "No tools provided to the Agent." in caplog.text
 
         # Patch agent.chat_generator.run to return mock_messages
         agent.chat_generator.run = MagicMock(return_value={"replies": mock_messages})