diff --git a/sdk/basyx/aas/backend/local_file.py b/sdk/basyx/aas/backend/local_file.py
index 4008497a..72d5605a 100644
--- a/sdk/basyx/aas/backend/local_file.py
+++ b/sdk/basyx/aas/backend/local_file.py
@@ -150,7 +150,7 @@ def __len__(self) -> int:
         :return: The number of objects (determined from the number of documents)
         """
         logger.debug("Fetching number of documents from database ...")
-        return len(os.listdir(self.directory_path))
+        return sum(1 for f in os.listdir(self.directory_path) if f.lower().endswith(".json"))
 
     def __iter__(self) -> Iterator[model.Identifiable]:
         """
@@ -161,7 +161,8 @@ def __iter__(self) -> Iterator[model.Identifiable]:
         """
         logger.debug("Iterating over objects in database ...")
         for name in os.listdir(self.directory_path):
-            yield self.get_identifiable_by_hash(name.rstrip(".json"))
+            if name.lower().endswith(".json"):
+                yield self.get_identifiable_by_hash(name[:-5])
 
     @staticmethod
     def _transform_id(identifier: model.Identifier) -> str:
diff --git a/sdk/test/backend/test_local_file.py b/sdk/test/backend/test_local_file.py
index adcbfcc7..f1080240 100644
--- a/sdk/test/backend/test_local_file.py
+++ b/sdk/test/backend/test_local_file.py
@@ -107,6 +107,33 @@ def test_key_errors(self) -> None:
         self.assertEqual("'No AAS object with id https://example.org/Test_Submodel exists in "
                          "local file database'", str(cm.exception))
 
+    def test_add_and_len_consistent(self) -> None:
+        # Each add() must increment len() by exactly 1
+        example_data = list(create_full_example())
+        for i, item in enumerate(example_data):
+            self.identifiable_store.add(item)
+            self.assertEqual(i + 1, len(self.identifiable_store))
+
+        # Stray non-json file must not be counted
+        stray = os.path.join(store_path, ".DS_Store")
+        with open(stray, "w") as f:
+            f.write("stray")
+        self.assertEqual(len(example_data), len(self.identifiable_store))
+        os.remove(stray)
+
+    def test_iter_ignores_non_json_files(self) -> None:
+        example_data = create_full_example()
+        for item in example_data:
+            self.identifiable_store.add(item)
+
+        # Stray files must not crash the iterator or be yielded
+        stray = os.path.join(store_path, ".DS_Store")
+        with open(stray, "w") as f:
+            f.write("stray")
+        items = list(self.identifiable_store)
+        self.assertEqual(5, len(items))
+        os.remove(stray)
+
     def test_reload_discard(self) -> None:
         # Load example submodel
         example_submodel = create_example_submodel()