diff --git a/pyaml/common/deprecation.py b/pyaml/common/deprecation.py
new file mode 100644
index 00000000..47961c01
--- /dev/null
+++ b/pyaml/common/deprecation.py
@@ -0,0 +1,20 @@
+"""
+PyAML deprecation helper.
+
+Thin re-export of :func:`typing_extensions.deprecated` (PEP 702), used to
+mark functions, methods and classes that are being phased out.
+
+The standard tool is used instead of a hand-rolled decorator because it
+preserves descriptor binding when composed with ``@classmethod``,
+``@staticmethod`` and ``@property``, warns on subclass creation as well as
+instantiation, sets the ``__deprecated__`` attribute, and lets static type
+checkers (mypy/pyright) flag call sites.
+
+``typing_extensions`` is used rather than ``typing`` so the helper is also
+available on Python < 3.13; the project therefore declares a direct
+dependency on ``typing_extensions >= 4.5``.
+"""
+
+from typing_extensions import deprecated
+
+__all__ = ["deprecated"]
diff --git a/pyproject.toml b/pyproject.toml
index 51ebb354..7994adca 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -30,7 +30,8 @@ dependencies = [
     "pydantic>=2.11.7",
     "accelerator-commissioning==1.5.3", #pySC
     "h5py",
-    "matplotlib"
+    "matplotlib",
+    "typing_extensions>=4.5"
 ]
 
 [project.optional-dependencies]
diff --git a/tests/common/test_deprecation.py b/tests/common/test_deprecation.py
new file mode 100644
index 00000000..ae9e5b6c
--- /dev/null
+++ b/tests/common/test_deprecation.py
@@ -0,0 +1,140 @@
+import warnings
+
+import pytest
+
+from pyaml.common.deprecation import deprecated
+
+
+def test_function_warns_and_returns_value():
+    @deprecated("old_func is deprecated")
+    def old_func(x):
+        return x * 2
+
+    with pytest.warns(DeprecationWarning, match=r"^old_func is deprecated$"):
+        assert old_func(3) == 6
+
+
+def test_custom_message_is_included():
+    @deprecated("use new_func instead")
+    def old_func():
+        return 1
+
+    with pytest.warns(DeprecationWarning, match=r"^use new_func instead$"):
+        old_func()
+
+
+def test_method_warns_with_given_message():
+    class Thing:
+        @deprecated("Thing.old is deprecated: use other()")
+        def old(self):
+            return "ok"
+
+    with pytest.warns(DeprecationWarning, match=r"^Thing\.old is deprecated: use other\(\)$"):
+        assert Thing().old() == "ok"
+
+
+def test_class_warns_on_instantiation_and_subclassing():
+    @deprecated("OldThing is deprecated: use NewThing")
+    class OldThing:
+        def __init__(self, value):
+            self.value = value
+
+    with pytest.warns(DeprecationWarning, match=r"^OldThing is deprecated: use NewThing$"):
+        obj = OldThing(5)
+    assert obj.value == 5
+
+    with pytest.warns(DeprecationWarning, match=r"^OldThing is deprecated: use NewThing$"):
+
+        class SubThing(OldThing):
+            pass
+
+
+def test_warning_points_at_caller():
+    @deprecated("old_func is deprecated")
+    def old_func():
+        return None
+
+    with warnings.catch_warnings(record=True) as record:
+        warnings.simplefilter("always")
+        old_func()
+    assert record[0].filename == __file__
+
+
+def test_wrapped_function_keeps_metadata():
+    @deprecated("documented is deprecated")
+    def documented():
+        """Docstring kept."""
+
+    assert documented.__name__ == "documented"
+    assert documented.__doc__ == "Docstring kept."
+    assert documented.__deprecated__ == "documented is deprecated"  # noqa: B009
+
+
+def test_classmethod_over_deprecated_binds_and_warns():
+    class Thing:
+        @classmethod
+        @deprecated("Thing.create is deprecated")
+        def create(cls):
+            return cls.__name__
+
+    with pytest.warns(DeprecationWarning, match=r"^Thing\.create is deprecated$"):
+        assert Thing.create() == "Thing"
+
+
+def test_deprecated_over_classmethod_fails_at_definition():
+    # typing_extensions.deprecated accepts classes and callables only; a
+    # classmethod descriptor object is neither, so this stacking order is
+    # rejected at class-definition time instead of silently losing binding.
+    with pytest.raises(TypeError, match="must be applied to a class or callable"):
+
+        class Thing:
+            @deprecated("Thing.create is deprecated")
+            @classmethod
+            def create(cls):
+                return cls.__name__
+
+
+def test_staticmethod_composes_in_both_orders():
+    class Thing:
+        @staticmethod
+        @deprecated("Thing.old_a is deprecated")
+        def old_a():
+            return "a"
+
+        @deprecated("Thing.old_b is deprecated")
+        @staticmethod
+        def old_b():
+            return "b"
+
+    with pytest.warns(DeprecationWarning, match=r"^Thing\.old_a is deprecated$"):
+        assert Thing.old_a() == "a"
+
+    with pytest.warns(DeprecationWarning, match=r"^Thing\.old_b is deprecated$"):
+        assert Thing.old_b() == "b"
+
+
+def test_property_over_deprecated_warns_on_access():
+    class Thing:
+        def __init__(self):
+            self._value = 7
+
+        @property
+        @deprecated("Thing.value is deprecated")
+        def value(self):
+            return self._value
+
+    thing = Thing()
+    with pytest.warns(DeprecationWarning, match=r"^Thing\.value is deprecated$"):
+        assert thing.value == 7
+
+
+def test_deprecated_over_property_fails_at_definition():
+    # A property object is not callable, so stacking @deprecated on top of
+    # @property is rejected at class-definition time; put @property on top.
+    with pytest.raises(TypeError, match="must be applied to a class or callable"):
+
+        class Thing:
+            @deprecated("Thing.value is deprecated")
+            @property
+            def value(self):
+                return 7