core[major]: only use function description (#21622)

Do not prefix function signature

---

* Reason for this is that information is already present with tool
calling models.
* This will save on tokens for those models, and makes it more obvious
what the description is!
* The @tool can get more parameters to allow a user to re-introduce the
the signature if we want

libs/core/langchain_core/tools.py

@@ -837,8 +837,7 @@ class StructuredTool(BaseTool):
 
         # Description example:
         # search_api(query: str) - Searches the API for the query.
-        sig = signature(source_function)
-        description_ = f"{name}{sig} - {description_.strip()}"
+        description_ = f"{description_.strip()}"
         _args_schema = args_schema
         if _args_schema is None and infer_schema:
             # schema name is appended within function
@@ -1057,7 +1056,16 @@ def render_text_description(tools: List[BaseTool]) -> str:
         search: This tool is used for search
         calculator: This tool is used for math
     """
-    return "\n".join([f"{tool.name}: {tool.description}" for tool in tools])
+    descriptions = []
+    for tool in tools:
+        if hasattr(tool, "func") and tool.func:
+            sig = signature(tool.func)
+            description = f"{tool.name}{sig} - {tool.description}"
+        else:
+            description = f"{tool.name} - {tool.description}"
+
+        descriptions.append(description)
+    return "\n".join(descriptions)
 
 
 def render_text_description_and_args(tools: List[BaseTool]) -> str:
@@ -1074,7 +1082,12 @@ args: {"expression": {"type": "string"}}
     tool_strings = []
     for tool in tools:
         args_schema = str(tool.args)
-        tool_strings.append(f"{tool.name}: {tool.description}, args: {args_schema}")
+        if hasattr(tool, "func") and tool.func:
+            sig = signature(tool.func)
+            description = f"{tool.name}{sig} - {tool.description}"
+        else:
+            description = f"{tool.name} - {tool.description}"
+        tool_strings.append(f"{description}, args: {args_schema}")
     return "\n".join(tool_strings)
 
 

libs/core/tests/unit_tests/test_tools.py

@@ -332,9 +332,8 @@ def test_structured_tool_from_function_docstring() -> None:
         "required": ["bar", "baz"],
     }
 
-    prefix = "foo(bar: int, baz: str) -> str - "
     assert foo.__doc__ is not None
-    assert structured_tool.description == prefix + textwrap.dedent(foo.__doc__.strip())
+    assert structured_tool.description == textwrap.dedent(foo.__doc__.strip())
 
 
 def test_structured_tool_from_function_docstring_complex_args() -> None:
@@ -365,9 +364,8 @@ def test_structured_tool_from_function_docstring_complex_args() -> None:
         "required": ["bar", "baz"],
     }
 
-    prefix = "foo(bar: int, baz: List[str]) -> str - "
     assert foo.__doc__ is not None
-    assert structured_tool.description == prefix + textwrap.dedent(foo.__doc__).strip()
+    assert structured_tool.description == textwrap.dedent(foo.__doc__).strip()
 
 
 def test_structured_tool_lambda_multi_args_schema() -> None:
@@ -700,9 +698,8 @@ def test_structured_tool_from_function() -> None:
         "required": ["bar", "baz"],
     }
 
-    prefix = "foo(bar: int, baz: str) -> str - "
     assert foo.__doc__ is not None
-    assert structured_tool.description == prefix + textwrap.dedent(foo.__doc__.strip())
+    assert structured_tool.description == textwrap.dedent(foo.__doc__.strip())
 
 
 def test_validation_error_handling_bool() -> None:
@@ -906,3 +903,15 @@ async def test_async_tool_pass_context() -> None:
     assert (
         await foo.ainvoke({"bar": "baz"}, {"configurable": {"foo": "not-bar"}}) == "baz"  # type: ignore
     )
+
+
+def test_tool_description() -> None:
+    def foo(bar: str) -> str:
+        """The foo."""
+        return bar
+
+    foo1 = tool(foo)
+    assert foo1.description == "The foo."  # type: ignore
+
+    foo2 = StructuredTool.from_function(foo)
+    assert foo2.description == "The foo."