diff --git a/fastapi/types.py b/fastapi/types.py
index 1fb86e13b1..9bab3ffd2a 100644
--- a/fastapi/types.py
+++ b/fastapi/types.py
@@ -1,3 +1,11 @@
+"""
+Internal type aliases for FastAPI.
+
+Provides shared type definitions used throughout the framework, including
+the decorated callable type variable, union type compatibility shim, and
+Pydantic model name mapping types.
+"""
+
 import types
 from collections.abc import Callable
 from enum import Enum