Improving the text of the invalid tool to list the available tools. (#8767)

Description: When using a ReAct Agent with tools and no tool is found,
the InvalidTool gets called. Previously it just asked for a different
action, but I've found that if you list the available actions it
improves the chances of getting a valid action in the next round. I've
added a UnitTest for it also.

@hinthornw

libs/langchain/langchain/agents/agent.py

@@ -897,7 +897,10 @@ s
             else:
                 tool_run_kwargs = self.agent.tool_run_logging_kwargs()
                 observation = InvalidTool().run(
-                    agent_action.tool,
+                    {
+                        "requested_tool_name": agent_action.tool,
+                        "available_tool_names": list(name_to_tool_map.keys()),
+                    },
                     verbose=self.verbose,
                     color=None,
                     callbacks=run_manager.get_child() if run_manager else None,
@@ -992,7 +995,10 @@ s
             else:
                 tool_run_kwargs = self.agent.tool_run_logging_kwargs()
                 observation = await InvalidTool().arun(
-                    agent_action.tool,
+                    {
+                        "requested_tool_name": agent_action.tool,
+                        "available_tool_names": list(name_to_tool_map.keys()),
+                    },
                     verbose=self.verbose,
                     color=None,
                     callbacks=run_manager.get_child() if run_manager else None,

libs/langchain/langchain/agents/tools.py

@@ -1,5 +1,5 @@
 """Interface for tools."""
-from typing import Optional
+from typing import List, Optional
 
 from langchain.callbacks.manager import (
     AsyncCallbackManagerForToolRun,
@@ -12,23 +12,33 @@ class InvalidTool(BaseTool):
     """Tool that is run when invalid tool name is encountered by agent."""
 
     name = "invalid_tool"
-    """Name of the tool."""
-    description = "Called when tool name is invalid."
-    """Description of the tool."""
+    description = "Called when tool name is invalid. Suggests valid tool names."
 
     def _run(
-        self, tool_name: str, run_manager: Optional[CallbackManagerForToolRun] = None
+        self,
+        requested_tool_name: str,
+        available_tool_names: List[str],
+        run_manager: Optional[CallbackManagerForToolRun] = None,
     ) -> str:
         """Use the tool."""
-        return f"{tool_name} is not a valid tool, try another one."
+        available_tool_names_str = ", ".join([tool for tool in available_tool_names])
+        return (
+            f"{requested_tool_name} is not a valid tool, "
+            f"try one of [{available_tool_names_str}]."
+        )
 
     async def _arun(
         self,
-        tool_name: str,
+        requested_tool_name: str,
+        available_tool_names: List[str],
         run_manager: Optional[AsyncCallbackManagerForToolRun] = None,
     ) -> str:
         """Use the tool asynchronously."""
-        return f"{tool_name} is not a valid tool, try another one."
+        available_tool_names_str = ", ".join([tool for tool in available_tool_names])
+        return (
+            f"{requested_tool_name} is not a valid tool, "
+            f"try one of [{available_tool_names_str}]."
+        )
 
 
 __all__ = ["InvalidTool", "BaseTool", "tool", "Tool"]

libs/langchain/tests/unit_tests/agents/test_agent.py

@@ -257,3 +257,26 @@ def test_agent_lookup_tool() -> None:
     )
 
     assert agent.lookup_tool("Search") == tools[0]
+
+
+def test_agent_invalid_tool() -> None:
+    """Test agent invalid tool and correct suggestions."""
+    fake_llm = FakeListLLM(responses=["FooBarBaz\nAction: Foo\nAction Input: Bar"])
+    tools = [
+        Tool(
+            name="Search",
+            func=lambda x: x,
+            description="Useful for searching",
+            return_direct=True,
+        ),
+    ]
+    agent = initialize_agent(
+        tools=tools,
+        llm=fake_llm,
+        agent=AgentType.ZERO_SHOT_REACT_DESCRIPTION,
+        return_intermediate_steps=True,
+        max_iterations=1,
+    )
+
+    resp = agent("when was langchain made")
+    resp["intermediate_steps"][0][1] == "Foo is not a valid tool, try one of [Search]."