diff --git a/homeassistant/helpers/llm.py b/homeassistant/helpers/llm.py
index bf89e693870..a8a598c79f8 100644
--- a/homeassistant/helpers/llm.py
+++ b/homeassistant/helpers/llm.py
@@ -331,7 +331,7 @@ class NamespacedTool(Tool):
     def __init__(self, namespace: str, tool: Tool) -> None:
         """Init the class."""
         self.namespace = namespace
-        self.name = f"{namespace}.{tool.name}"
+        self.name = f"{namespace}__{tool.name}"
         self.description = tool.description
         self.parameters = tool.parameters
         self.tool = tool
@@ -915,7 +915,7 @@ class ActionTool(Tool):
         """Init the class."""
         self._domain = domain
         self._action = action
-        self.name = f"{domain}.{action}"
+        self.name = f"{domain}__{action}"
         # Note: _get_cached_action_parameters only works for services which
         # add their description directly to the service description cache.
         # This is not the case for most services, but it is for scripts.
diff --git a/tests/helpers/test_llm.py b/tests/helpers/test_llm.py
index b978559130c..78ff675f0b6 100644
--- a/tests/helpers/test_llm.py
+++ b/tests/helpers/test_llm.py
@@ -1542,18 +1542,18 @@ This is prompt 2
 """
     )
     assert [(tool.name, tool.description) for tool in instance.tools] == [
-        ("api-1.Tool_1", "Description 1"),
-        ("api-2.Tool_2", "Description 2"),
+        ("api-1__Tool_1", "Description 1"),
+        ("api-2__Tool_2", "Description 2"),
     ]
 
     # The test tool returns back the provided arguments so we can verify
     # the original tool is invoked with the correct tool name and args.
     result = await instance.async_call_tool(
-        llm.ToolInput(tool_name="api-1.Tool_1", tool_args={"arg1": "value1"})
+        llm.ToolInput(tool_name="api-1__Tool_1", tool_args={"arg1": "value1"})
     )
     assert result == {"result": {"Tool_1": {"arg1": "value1"}}}
 
     result = await instance.async_call_tool(
-        llm.ToolInput(tool_name="api-2.Tool_2", tool_args={"arg2": "value2"})
+        llm.ToolInput(tool_name="api-2__Tool_2", tool_args={"arg2": "value2"})
     )
     assert result == {"result": {"Tool_2": {"arg2": "value2"}}}