diff --git a/docs/CHANGELOG.md b/docs/CHANGELOG.md
index 713a508..761548a 100644
--- a/docs/CHANGELOG.md
+++ b/docs/CHANGELOG.md
@@ -5,4 +5,5 @@
 ### Added
 
 - Add class for existing directories
-- Add function to format a list human-readable
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+- Add function to format a list human-readable
+- Add function to assert that an object is an instance of a specific type
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diff --git a/src/jcloud_docsgen/utils.py b/src/jcloud_docsgen/utils.py
index 3e91789..a9ad557 100644
--- a/src/jcloud_docsgen/utils.py
+++ b/src/jcloud_docsgen/utils.py
@@ -82,4 +82,37 @@ def human_readable_list(ls: list, final_separator: str = 'and', quotation_mark:
             _quote(str(obj), quotation_mark) # quote the string representation of the object
             for obj in ls[:-1] # do not include the last element of the list
         ]
-    ) + ' ' + final_separator + ' ' + _quote(str(ls[-1]), quotation_mark)
\ No newline at end of file
+    ) + ' ' + final_separator + ' ' + _quote(str(ls[-1]), quotation_mark)
+
+def _list_type_names(types: list[type]) -> list[str]:
+    '''
+    Converts a list of types into a list of their names (``__name__``
+    attribute)
+
+    :param types: The list of types
+    :type types: list[type]
+
+    :return: The list of the names of the types
+    :rtype: list[str]
+    '''
+
+    return [tp.__name__ for tp in types]
+
+def assert_that_is_instance(obj: object, class_or_tuple: Union[type, types.UnionType, tuple[type, ...]]) -> None:
+    if not isinstance(class_or_tuple, Union[type, types.UnionType, tuple]):
+        raise TypeError(f'class_or_tuple: expected \'Union[type, types.UnionType, tuple[type, ...]]\', \'got {type(class_or_tuple).__name__}\'')
+    if not isinstance(obj, class_or_tuple):
+        if isinstance(class_or_tuple, (tuple, types.UnionType)):
+            print('MORE')
+            if isinstance(class_or_tuple, types.UnionType):
+                class_or_tuple = class_or_tuple.__args__
+                print('LIST:', _list_type_names(class_or_tuple))
+            if len(class_or_tuple) > 1:
+                exception_message_expected = 'either '
+            else:
+                exception_message_expected = ''
+            exception_message_expected += human_readable_list(_list_type_names(class_or_tuple), 'or', '\'')
+        else:
+            print('SINGLE')
+            exception_message_expected = '\'' + class_or_tuple.__name__ + '\''
+        raise TypeError(f'expected {exception_message_expected}, got \'{type(obj).__name__}\'')
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diff --git a/tests/unit/_utils/test_assert_that_is_instance.py b/tests/unit/_utils/test_assert_that_is_instance.py
new file mode 100644
index 0000000..580e121
--- /dev/null
+++ b/tests/unit/_utils/test_assert_that_is_instance.py
@@ -0,0 +1,29 @@
+from src.jcloud_docsgen.utils import assert_that_is_instance
+import pytest
+import types
+
+class TestType: ...
+TestType.__name__ = 'NOT TestType'
+
+@pytest.mark.parametrize('obj,class_or_tuple', [
+    (1, int),
+    (1, (int,)),
+    (1, str | int),
+    (1, int | str | list),
+    (TestType(), TestType),
+    (None, types.NoneType),
+])
+def test_assert_that_is_instance(obj, class_or_tuple):
+    assert_that_is_instance(obj, class_or_tuple)
+
+@pytest.mark.parametrize('obj,class_or_tuple,expected_exception_msg', [
+    (1, str, 'expected \'str\', got \'int\''),
+    (1, (str,), 'expected \'str\', got \'int\''),
+    (1, str | float, 'expected either \'str\' or \'float\', got \'int\''),
+    (1, str | float | list, 'expected either \'str\', \'float\' or \'list\', got \'int\''),
+    (1, TestType, 'expected \'NOT TestType\', got \'int\''),
+])
+def test_assert_that_is_instance_exceptions(obj, class_or_tuple, expected_exception_msg):
+    with pytest.raises(TypeError) as exc_info:
+        assert_that_is_instance(obj, class_or_tuple)
+    assert str(exc_info.value) == expected_exception_msg
\ No newline at end of file