diff --git a/src/pynxtools/dataconverter/helpers.py b/src/pynxtools/dataconverter/helpers.py
index 2f6d56cdb..50c2f6e56 100644
--- a/src/pynxtools/dataconverter/helpers.py
+++ b/src/pynxtools/dataconverter/helpers.py
@@ -884,6 +884,12 @@ def update_and_warn(key: str, value: str, overwrite=False):
         get_nexus_version(),
         overwrite=False,
     )
+    update_and_warn(
+        f"/ENTRY[{entry_name}]/definition/@URL",
+        "https://github.com/FAIRmat-NFDI/nexus_definitions/"
+        f"blob/{get_nexus_version_hash()}",
+        overwrite=False,
+    )
 
 
 def extract_atom_types(formula, mode="hill"):
diff --git a/src/pynxtools/dataconverter/validation.py b/src/pynxtools/dataconverter/validation.py
index ccf41abfb..63a715f6a 100644
--- a/src/pynxtools/dataconverter/validation.py
+++ b/src/pynxtools/dataconverter/validation.py
@@ -25,7 +25,6 @@
 import h5py
 import lxml.etree as ET
 import numpy as np
-from anytree import Resolver
 
 from pynxtools.dataconverter.helpers import (
     Collector,