diff --git a/src/google/adk/tools/function_tool.py b/src/google/adk/tools/function_tool.py
index b1cd8e4..069108c 100644
--- a/src/google/adk/tools/function_tool.py
+++ b/src/google/adk/tools/function_tool.py
@@ -34,15 +34,27 @@ class FunctionTool(BaseTool):
 
   def __init__(self, func: Callable[..., Any]):
     """Extract metadata from a callable object."""
-    if inspect.isfunction(func) or inspect.ismethod(func):
-      # Handle regular functions and methods
+    name = ''
+    doc = ''
+    # Handle different types of callables
+    if hasattr(func, '__name__'):
+      # Regular functions, unbound methods, etc.
       name = func.__name__
-      doc = func.__doc__ or ''
-    else:
-      # Handle objects with __call__ method
-      call_method = func.__call__
+    elif hasattr(func, '__class__'):
+      # Callable objects, bound methods, etc.
       name = func.__class__.__name__
-      doc = call_method.__doc__ or func.__doc__ or ''
+
+    # Get documentation (prioritize direct __doc__ if available)
+    if hasattr(func, '__doc__') and func.__doc__:
+      doc = func.__doc__
+    elif (
+        hasattr(func, '__call__')
+        and hasattr(func.__call__, '__doc__')
+        and func.__call__.__doc__
+    ):
+      # For callable objects, try to get docstring from __call__ method
+      doc = func.__call__.__doc__
+
     super().__init__(name=name, description=doc)
     self.func = func
 
diff --git a/tests/unittests/tools/test_function_tool.py b/tests/unittests/tools/test_function_tool.py
index 950e388..ece1f53 100644
--- a/tests/unittests/tools/test_function_tool.py
+++ b/tests/unittests/tools/test_function_tool.py
@@ -41,6 +41,10 @@ async def async_function_for_testing_with_2_arg_and_no_tool_context(arg1, arg2):
 
 class AsyncCallableWith2ArgsAndNoToolContext:
 
+  def __init__(self):
+    self.__name__ = "Async callable name"
+    self.__doc__ = "Async callable doc"
+
   async def __call__(self, arg1, arg2):
     assert arg1
     assert arg2
@@ -57,6 +61,7 @@ def function_for_testing_with_1_arg_and_tool_context(arg1, tool_context):
 class AsyncCallableWith1ArgAndToolContext:
 
   async def __call__(self, arg1, tool_context):
+    """Async call doc"""
     assert arg1
     assert tool_context
     return arg1
@@ -107,6 +112,8 @@ async def test_run_async_with_tool_context_async_callable():
   args = {"arg1": "test_value_1"}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == "test_value_1"
+  assert tool.name == "AsyncCallableWith1ArgAndToolContext"
+  assert tool.description == "Async call doc"
 
 
 @pytest.mark.asyncio
@@ -125,6 +132,8 @@ async def test_run_async_without_tool_context_async_callable():
   args = {"arg1": "test_value_1", "arg2": "test_value_2"}
   result = await tool.run_async(args=args, tool_context=MagicMock())
   assert result == "test_value_1"
+  assert tool.name == "Async callable name"
+  assert tool.description == "Async callable doc"
 
 
 @pytest.mark.asyncio