diff --git a/src/gmdkit/utils/obj_field.py b/src/gmdkit/utils/obj_field.py
new file mode 100644
index 0000000..648c1fe
--- /dev/null
+++ b/src/gmdkit/utils/obj_field.py
@@ -0,0 +1,20 @@
+
+from typing import Any, TypeVar, Generic, overload
+
+T = TypeVar("T")
+
+class ObjField(Generic[T]):
+    def __init__(self, key: Any) -> None:
+        self.key = key
+
+    @overload
+    def __get__(self, instance: None, owner: type[Any]) -> "ObjField[T]": ...
+    @overload
+    def __get__(self, instance: object, owner: type[Any] | None = None) -> T: ...
+    def __get__(self, instance: object | None, owner: type[Any] | None = None) -> T | "ObjField[T]":
+        if instance is None:
+            return self
+        return instance.obj[self.key] # type: ignore[attr-defined]
+
+    def __set__(self, instance: Any, value: T) -> None:
+        instance.obj[self.key] = value
\ No newline at end of file