diff --git a/.gitignore b/.gitignore
index bd139eea0..109f11c48 100644
--- a/.gitignore
+++ b/.gitignore
@@ -202,6 +202,8 @@ cython_debug/
 !dev-requirements.txt
 !mkdocs-requirements.txt
 !src/pynxtools/nexus-version.txt
+!src/pynxtools/dataconverter/units/constants_en.txt
+!src/pynxtools/dataconverter/units/default_en.txt
 build/
 nexusparser.egg-info/PKG-INFO
 .python-version
diff --git a/MANIFEST.in b/MANIFEST.in
index 7b8255ac3..69c36fbb7 100644
--- a/MANIFEST.in
+++ b/MANIFEST.in
@@ -9,5 +9,6 @@ recursive-include src/pynxtools/definitions/applications/ *.xml
 recursive-include src/pynxtools/definitions/contributed_definitions/ *.xml
 include src/pynxtools/definitions/*.xsd
 include src/pynxtools/nexus-version.txt
+include src/pynxtools/dataconverter/units *.txt
 include src/pynxtools/definitions/NXDL_VERSION
 
diff --git a/dev-requirements.txt b/dev-requirements.txt
index 27205fe2c..637c54026 100644
--- a/dev-requirements.txt
+++ b/dev-requirements.txt
@@ -2,10 +2,14 @@
 #    uv pip compile --extra=dev --extra=docs --output-file=dev-requirements.txt pyproject.toml
 anytree==2.12.1
     # via pynxtools (pyproject.toml)
+appdirs==1.4.4
+    # via pint
 ase==3.23.0
     # via pynxtools (pyproject.toml)
 babel==2.15.0
     # via mkdocs-material
+cachetools==5.4.0
+    # via pynxtools (pyproject.toml)
 certifi==2024.7.4
     # via requests
 cfgv==3.4.0
@@ -34,6 +38,10 @@ exceptiongroup==1.2.1
     # via pytest
 filelock==3.15.4
     # via virtualenv
+flexcache==0.3
+    # via pint
+flexparser==0.3.1
+    # via pint
 fonttools==4.53.1
     # via matplotlib
 ghp-import==2.1.0
@@ -123,6 +131,8 @@ pathspec==0.12.1
     # via mkdocs
 pillow==10.4.0
     # via matplotlib
+pint==0.24.3
+    # via pynxtools (pyproject.toml)
 platformdirs==4.2.2
     # via
     #   mkdocs-get-deps
@@ -169,7 +179,7 @@ regex==2024.5.15
     # via mkdocs-material
 requests==2.32.3
     # via mkdocs-material
-ruff==0.4.8
+ruff==0.5.5
     # via pynxtools (pyproject.toml)
 scipy==1.14.0
     # via ase
@@ -193,7 +203,11 @@ types-pyyaml==6.0.12.20240311
 types-requests==2.32.0.20240622
     # via pynxtools (pyproject.toml)
 typing-extensions==4.12.2
-    # via mypy
+    # via
+    #   flexcache
+    #   flexparser
+    #   mypy
+    #   pint
 tzdata==2024.1
     # via pandas
 urllib3==2.2.2
diff --git a/pyproject.toml b/pyproject.toml
index 307fb5918..85478ab23 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -35,6 +35,8 @@ dependencies = [
     "importlib-metadata",
     "lxml>=4.9.1",
     "anytree",
+    "cachetools",
+    "pint>=0.17",
 ]
 
 [project.urls]
@@ -98,9 +100,11 @@ nexus_data_converter = "pynxtools.nomad.entrypoints:nexus_data_converter"
 read_nexus = "pynxtools.nexus.nexus:main"
 dataconverter = "pynxtools.dataconverter.convert:main_cli"
 generate_eln = "pynxtools.eln_mapper.eln_mapper:get_eln"
+verify_nexus = "pynxtools.dataconverter.verify:verify"
 
 [tool.setuptools.package-data]
 pynxtools = ["definitions/**/*.xml", "definitions/**/*.xsd"]
+"pynxtools.dataconverter.units" = ["*.txt"]
 "pynxtools.dataconverter.readers.hall" = ["enum_map.json"]
 "pynxtools.dataconverter.readers.rii_database.formula_parser" = ["dispersion_function_grammar.lark"]
 
diff --git a/src/pynxtools/dataconverter/helpers.py b/src/pynxtools/dataconverter/helpers.py
index 27f051e22..b0bbd9103 100644
--- a/src/pynxtools/dataconverter/helpers.py
+++ b/src/pynxtools/dataconverter/helpers.py
@@ -31,7 +31,14 @@
 import numpy as np
 from ase.data import chemical_symbols
 
+if np.lib.NumpyVersion(np.__version__) < "2.0.0":
+    from numpy import chararray
+else:
+    from numpy.char import chararray
+from pint import UndefinedUnitError
+
 from pynxtools import get_nexus_version, get_nexus_version_hash
+from pynxtools.dataconverter.units import ureg
 from pynxtools.definitions.dev_tools.utils.nxdl_utils import (
     get_enums,
     get_inherited_nodes,
@@ -91,10 +98,7 @@ def _log(self, path: str, log_type: ValidationProblem, value: Optional[Any], *ar
         elif log_type == ValidationProblem.MissingRequiredGroup:
             logger.warning(f"The required group, {path}, hasn't been supplied.")
         elif log_type == ValidationProblem.MissingRequiredField:
-            logger.warning(
-                f"The data entry corresponding to {path} is required "
-                "and hasn't been supplied by the reader.",
-            )
+            logger.warning(f"Missing field: {path}")
         elif log_type == ValidationProblem.InvalidType:
             logger.warning(
                 f"The value at {path} should be one of: {value}"
@@ -299,24 +303,35 @@ def get_nxdl_root_and_path(nxdl: str):
     special_names = {
         "NXtest": os.path.join(data_path, "NXtest.nxdl.xml"),
         "NXtest_extended": os.path.join(data_path, "NXtest_extended.nxdl.xml"),
+        "NXhdf5_validator_1": os.path.join(data_path, "NXhdf5_validator_1.nxdl.xml"),
+        "NXhdf5_validator_2": os.path.join(data_path, "NXhdf5_validator_2.nxdl.xml"),
     }
 
+    probable_file_paths = [
+        os.path.join(definitions_path, "contributed_definitions", f"{nxdl}.nxdl.xml"),
+        os.path.join(definitions_path, "applications", f"{nxdl}.nxdl.xml"),
+        os.path.join(definitions_path, "base_classes", f"{nxdl}.nxdl.xml"),
+        os.path.join(
+            definitions_path, "dev_tools/tests/test_nxdls", f"{nxdl}.nxdl.xml"
+        ),
+    ]
     if nxdl in special_names:
         nxdl_f_path = special_names[nxdl]
     else:
-        nxdl_f_path = os.path.join(
-            definitions_path, "contributed_definitions", f"{nxdl}.nxdl.xml"
-        )
-        if not os.path.exists(nxdl_f_path):
-            nxdl_f_path = os.path.join(
-                definitions_path, "applications", f"{nxdl}.nxdl.xml"
-            )
-        if not os.path.exists(nxdl_f_path):
-            nxdl_f_path = os.path.join(
-                definitions_path, "base_classes", f"{nxdl}.nxdl.xml"
-            )
-        if not os.path.exists(nxdl_f_path):
-            raise FileNotFoundError(f"The nxdl file, {nxdl}, was not found.")
+        nxdl_f_path = next(x for x in probable_file_paths if os.path.exists(x))
+        # nxdl_f_path = os.path.join(
+        #     definitions_path, "contributed_definitions", f"{nxdl}.nxdl.xml"
+        # )
+        # if not os.path.exists(nxdl_f_path):
+        #     nxdl_f_path = os.path.join(
+        #         definitions_path, "applications", f"{nxdl}.nxdl.xml"
+        #     )
+        # if not os.path.exists(nxdl_f_path):
+        #     nxdl_f_path = os.path.join(
+        #         definitions_path, "base_classes", f"{nxdl}.nxdl.xml"
+        #     )
+        # if not os.path.exists(nxdl_f_path):
+        #     raise FileNotFoundError(f"The nxdl file, {nxdl}, was not found.")
 
     return ET.parse(nxdl_f_path).getroot(), nxdl_f_path
 
@@ -582,7 +597,7 @@ def is_value_valid_element_of_enum(value, elist) -> Tuple[bool, list]:
     "ISO8601": (str,),
     "NX_BINARY": (bytes, bytearray, np.byte, np.ubyte, np.ndarray),
     "NX_BOOLEAN": (bool, np.ndarray, np.bool_),
-    "NX_CHAR": (str, np.ndarray, np.chararray),
+    "NX_CHAR": (str, np.ndarray, chararray),
     "NX_DATE_TIME": (str,),
     "NX_FLOAT": (float, np.ndarray, np.floating),
     "NX_INT": (int, np.ndarray, np.signedinteger),
@@ -647,6 +662,63 @@ def convert_str_to_bool_safe(value):
     return None
 
 
+def clean_str_attr(
+    attr: Optional[Union[str, bytes]], encoding="utf-8"
+) -> Optional[str]:
+    """
+    Cleans the string attribute which means it will decode bytes to str if necessary.
+    If `attr` is not str, bytes or None it raises a TypeError.
+    """
+    if attr is None:
+        return attr
+    if isinstance(attr, bytes):
+        return attr.decode(encoding)
+    if isinstance(attr, str):
+        return attr
+
+    raise TypeError(
+        "Invalid type {type} for attribute. Should be either None, bytes or str."
+    )
+
+
+def is_valid_unit(
+    unit: str, nx_category: str, transformation_type: Optional[str]
+) -> bool:
+    """
+    The provided unit belongs to the provided nexus unit category.
+    Args:
+        unit (str): The unit to check. Should be according to pint.
+        nx_category (str): A nexus unit category, e.g. `NX_LENGTH`,
+            or derived unit category, e.g., `NX_LENGTH ** 2`.
+        transformation_type (Optional[str]):
+            The transformation type of an NX_TRANSFORMATION.
+            This parameter is ignored if the `nx_category` is not `NX_TRANSFORMATION`.
+            If `transformation_type` is not present this should be set to None.
+    Returns:
+        bool: The unit belongs to the provided category
+    """
+    unit = clean_str_attr(unit)
+    try:
+        if nx_category in ("NX_ANY"):
+            ureg(unit)  # Check if unit is generally valid
+            return True
+        nx_category = re.sub(r"(NX_[A-Z]+)", r"[\1]", nx_category)
+        if nx_category == "[NX_TRANSFORMATION]":
+            # NX_TRANSFORMATIONS is a pseudo unit
+            # and can be either an angle, a length or unitless
+            # depending on the transformation type.
+            if transformation_type is None:
+                return ureg(unit).check("[NX_UNITLESS]")
+            if transformation_type == "translation":
+                return ureg(unit).check("[NX_LENGTH]")
+            if transformation_type == "rotation":
+                return ureg(unit).check("[NX_ANGLE]")
+            return False
+        return ureg(unit).check(f"{nx_category}")
+    except UndefinedUnitError:
+        return False
+
+
 def is_valid_data_field(value, nxdl_type, path) -> bool:
     """Checks whether a given value is valid according to what is defined in the NXDL.
 
diff --git a/src/pynxtools/dataconverter/nexus_tree.py b/src/pynxtools/dataconverter/nexus_tree.py
index bbba22c09..24cb91753 100644
--- a/src/pynxtools/dataconverter/nexus_tree.py
+++ b/src/pynxtools/dataconverter/nexus_tree.py
@@ -29,7 +29,7 @@
 """
 
 from functools import reduce
-from typing import Any, List, Literal, Optional, Set, Tuple, Union
+from typing import Any, List, Literal, Optional, Set, Tuple
 
 import lxml.etree as ET
 from anytree.node.nodemixin import NodeMixin
@@ -142,18 +142,24 @@ class NexusNode(NodeMixin):
             The inverse of the above `is_a`. In the example case
             `DATA` `parent_of` `my_data`.
     """
-
+    # TODO rename type to nx_type in every place
     name: str
     type: Literal["group", "field", "attribute", "choice"]
     optionality: Literal["required", "recommended", "optional"] = "required"
+    name_type: Literal["any", "partial"]
     variadic: bool = False
     inheritance: List[ET._Element]
     is_a: List["NexusNode"]
     parent_of: List["NexusNode"]
+    occurrence_limits: Tuple[
+        # TODO: Use Annotated[int, Field(strict=True, ge=0)] for py>3.8
+        Optional[int],
+        Optional[int],
+    ] = (None, None)
 
     def _set_optionality(self):
         """
-        Sets the optionality of the current node
+        Sets the optionality of the current node based on the inheritance chain.
         if `recommended`, `required` or `optional` is set.
         Also sets the field to optional if `maxOccurs == 0` or to required
         if `maxOccurs > 0`.
@@ -179,6 +185,7 @@ def __init__(
         type: Literal["group", "field", "attribute", "choice"],
         optionality: Literal["required", "recommended", "optional"] = "required",
         variadic: Optional[bool] = None,
+        name_type: Optional[Literal["any", "partial"]] = None,
         parent: Optional["NexusNode"] = None,
         inheritance: Optional[List[Any]] = None,
     ) -> None:
@@ -187,6 +194,7 @@ def __init__(
         self.type = type
         self.optionality = optionality
         self.variadic = contains_uppercase(self.name)
+        self.name_type = name_type
         if variadic is not None:
             self.variadic = variadic
         if inheritance is not None:
@@ -222,6 +230,9 @@ def get_path(self) -> str:
         while current_node.parent is not None:
             names.insert(0, current_node.name)
             current_node = current_node.parent
+
+        if self.type == "attribute" and names:
+            names[-1] = f"@{names[-1]}"
         return "/" + "/".join(names)
 
     def search_add_child_for_multiple(
@@ -793,10 +804,10 @@ def _set_items(self):
         if not self.dtype == "NX_CHAR":
             return
         for elem in self.inheritance:
-            enum = elem.find(f"nx:enumeration", namespaces=namespaces)
+            enum = elem.find("nx:enumeration", namespaces=namespaces)
             if enum is not None:
                 self.items = []
-                for items in enum.findall(f"nx:item", namespaces=namespaces):
+                for items in enum.findall("nx:item", namespaces=namespaces):
                     self.items.append(items.attrib["value"])
                 return
 
@@ -806,7 +817,7 @@ def _set_shape(self):
         The first vale found is used.
         """
         for elem in self.inheritance:
-            dimension = elem.find(f"nx:dimensions", namespaces=namespaces)
+            dimension = elem.find("nx:dimensions", namespaces=namespaces)
             if dimension is not None:
                 break
         if not self.inheritance or dimension is None:
diff --git a/src/pynxtools/dataconverter/readers/example/reader.py b/src/pynxtools/dataconverter/readers/example/reader.py
index 34d0aae1c..3e3fd09af 100644
--- a/src/pynxtools/dataconverter/readers/example/reader.py
+++ b/src/pynxtools/dataconverter/readers/example/reader.py
@@ -15,7 +15,6 @@
 # See the License for the specific language governing permissions and
 # limitations under the License.
 
-#
 """An example reader implementation for the DataConverter."""
 
 import json
diff --git a/src/pynxtools/dataconverter/units/__init__.py b/src/pynxtools/dataconverter/units/__init__.py
new file mode 100644
index 000000000..90230a882
--- /dev/null
+++ b/src/pynxtools/dataconverter/units/__init__.py
@@ -0,0 +1,24 @@
+#
+# Copyright The NOMAD Authors.
+#
+# This file is part of NOMAD. See https://nomad-lab.eu for further info.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""A unit registry for nexus units"""
+
+import os
+
+from pint import UnitRegistry
+
+ureg = UnitRegistry(os.path.join(os.path.dirname(__file__), "default_en.txt"))
diff --git a/src/pynxtools/dataconverter/units/constants_en.txt b/src/pynxtools/dataconverter/units/constants_en.txt
new file mode 100644
index 000000000..6ec8d2dbc
--- /dev/null
+++ b/src/pynxtools/dataconverter/units/constants_en.txt
@@ -0,0 +1,72 @@
+# Default Pint constants definition file
+# Based on the International System of Units
+# Language: english
+# Source: https://physics.nist.gov/cuu/Constants/
+#         https://physics.nist.gov/PhysRefData/XrayTrans/Html/search.html
+# :copyright: 2013,2019 by Pint Authors, see AUTHORS for more details.
+
+#### MATHEMATICAL CONSTANTS ####
+# As computed by Maxima with fpprec:50
+
+pi     = 3.1415926535897932384626433832795028841971693993751 = π  # pi
+tansec = 4.8481368111333441675396429478852851658848753880815e-6   # tangent of 1 arc-second ~ arc_second/radian
+ln10   = 2.3025850929940456840179914546843642076011014886288      # natural logarithm of 10
+wien_x = 4.9651142317442763036987591313228939440555849867973      # solution to (x-5)*exp(x)+5 = 0 => x = W(5/exp(5))+5
+wien_u = 2.8214393721220788934031913302944851953458817440731      # solution to (u-3)*exp(u)+3 = 0 => u = W(3/exp(3))+3
+
+#### DEFINED EXACT CONSTANTS ####
+
+speed_of_light = 299792458 m/s = c = c_0                      # since 1983
+planck_constant = 6.62607015e-34 J s = h                      # since May 2019
+elementary_charge = 1.602176634e-19 C = e                     # since May 2019
+avogadro_number = 6.02214076e23                               # since May 2019
+boltzmann_constant = 1.380649e-23 J K^-1 = k = k_B            # since May 2019
+standard_gravity = 9.80665 m/s^2 = g_0 = g0 = g_n = gravity   # since 1901
+standard_atmosphere = 1.01325e5 Pa = atm = atmosphere         # since 1954
+conventional_josephson_constant = 4.835979e14 Hz / V = K_J90  # since Jan 1990
+conventional_von_klitzing_constant = 2.5812807e4 ohm = R_K90  # since Jan 1990
+
+#### DERIVED EXACT CONSTANTS ####
+# Floating-point conversion may introduce inaccuracies
+
+zeta = c / (cm/s) = ζ
+dirac_constant = h / (2 * π) = ħ = h_bar = atomic_unit_of_action = a_u_action
+avogadro_constant = avogadro_number * mol^-1 = N_A
+molar_gas_constant = k * N_A = R
+faraday_constant = e * N_A
+conductance_quantum = 2 * e ** 2 / h = G_0
+magnetic_flux_quantum = h / (2 * e) = Φ_0 = Phi_0
+josephson_constant = 2 * e / h = K_J
+von_klitzing_constant = h / e ** 2 = R_K
+stefan_boltzmann_constant = 2 / 15 * π ** 5 * k ** 4 / (h ** 3 * c ** 2) = σ = sigma
+first_radiation_constant = 2 * π * h * c ** 2 = c_1
+second_radiation_constant = h * c / k = c_2
+wien_wavelength_displacement_law_constant = h * c / (k * wien_x)
+wien_frequency_displacement_law_constant = wien_u * k / h
+
+#### MEASURED CONSTANTS ####
+# Recommended CODATA-2018 values
+# To some extent, what is measured and what is derived is a bit arbitrary.
+# The choice of measured constants is based on convenience and on available uncertainty.
+# The uncertainty in the last significant digits is given in parentheses as a comment.
+
+newtonian_constant_of_gravitation = 6.67430e-11 m^3/(kg s^2) = _ = gravitational_constant  # (15)
+rydberg_constant = 1.0973731568160e7 * m^-1 = R_∞ = R_inf                                  # (21)
+electron_g_factor = -2.00231930436256 = g_e                                                # (35)
+atomic_mass_constant = 1.66053906660e-27 kg = m_u                                          # (50)
+electron_mass = 9.1093837015e-31 kg = m_e = atomic_unit_of_mass = a_u_mass                 # (28)
+proton_mass = 1.67262192369e-27 kg = m_p                                                   # (51)
+neutron_mass = 1.67492749804e-27 kg = m_n                                                  # (95)
+K_alpha_Cu_d_220 = 0.80232719                                                              # (22)
+K_alpha_Mo_d_220 = 0.36940604                                                              # (19)
+K_alpha_W_d_220 = 0.108852175                                                              # (98)
+
+#### DERIVED CONSTANTS ####
+
+fine_structure_constant = (2 * h * R_inf / (m_e * c)) ** 0.5 = α = alpha
+vacuum_permeability = 2 * α * h / (e ** 2 * c) = µ_0 = mu_0 = mu0 = magnetic_constant
+vacuum_permittivity = e ** 2 / (2 * α * h * c) = ε_0 = epsilon_0 = eps_0 = eps0 = electric_constant
+impedance_of_free_space = 2 * α * h / e ** 2 = Z_0 = characteristic_impedance_of_vacuum
+coulomb_constant = α * h_bar * c / e ** 2 = k_C
+classical_electron_radius = α * h_bar / (m_e * c) = r_e
+thomson_cross_section = 8 / 3 * π * r_e ** 2 = σ_e = sigma_e
diff --git a/src/pynxtools/dataconverter/units/default_en.txt b/src/pynxtools/dataconverter/units/default_en.txt
new file mode 100644
index 000000000..dc9c58685
--- /dev/null
+++ b/src/pynxtools/dataconverter/units/default_en.txt
@@ -0,0 +1,634 @@
+# Default Pint units definition file
+# Based on the International System of Units
+# Language: english
+# :copyright: 2013,2019 by Pint Authors, see AUTHORS for more details.
+
+# Syntax
+# ======
+# Units
+# -----
+# <canonical name> = <relation to another unit or dimension> [= <symbol>] [= <alias>] [ = <alias> ] [...]
+#
+# The canonical name and aliases should be expressed in singular form.
+# Pint automatically deals with plurals built by adding 's' to the singular form; plural
+# forms that don't follow this rule should be instead explicitly listed as aliases.
+#
+# If a unit has no symbol and one wants to define aliases, then the symbol should be
+# conventionally set to _.
+#
+# Example:
+#     millennium = 1e3 * year = _ = millennia
+#
+#
+# Prefixes
+# --------
+# <prefix>- = <amount> [= <symbol>] [= <alias>] [ = <alias> ] [...]
+#
+# Example:
+#     deca- =  1e+1  = da- = deka-
+#
+#
+# Derived dimensions
+# ------------------
+# [dimension name] = <relation to other dimensions>
+#
+# Example:
+#     [density] = [mass] / [volume]
+#
+# Note that primary dimensions don't need to be declared; they can be
+# defined for the first time in a unit definition.
+# E.g. see below `meter = [length]`
+#
+#
+# Additional aliases
+# ------------------
+# @alias <canonical name or previous alias> = <alias> [ = <alias> ] [...]
+#
+# Used to add aliases to already existing unit definitions.
+# Particularly useful when one wants to enrich definitions
+# from defaults_en.txt with custom aliases.
+#
+# Example:
+#     @alias meter = my_meter
+
+# See also: https://pint.readthedocs.io/en/latest/defining.html
+
+@defaults
+    group = international
+    system = mks
+@end
+
+
+#### PREFIXES ####
+
+# decimal prefixes
+yocto- = 1e-24 = y-
+zepto- = 1e-21 = z-
+atto- =  1e-18 = a-
+femto- = 1e-15 = f-
+pico- =  1e-12 = p-
+nano- =  1e-9  = n-
+micro- = 1e-6  = µ- = u-
+milli- = 1e-3  = m-
+centi- = 1e-2  = c-
+deci- =  1e-1  = d-
+deca- =  1e+1  = da- = deka-
+hecto- = 1e2   = h-
+kilo- =  1e3   = k-
+mega- =  1e6   = M-
+giga- =  1e9   = G-
+tera- =  1e12  = T-
+peta- =  1e15  = P-
+exa- =   1e18  = E-
+zetta- = 1e21  = Z-
+yotta- = 1e24  = Y-
+
+# binary_prefixes
+kibi- = 2**10 = Ki-
+mebi- = 2**20 = Mi-
+gibi- = 2**30 = Gi-
+tebi- = 2**40 = Ti-
+pebi- = 2**50 = Pi-
+exbi- = 2**60 = Ei-
+zebi- = 2**70 = Zi-
+yobi- = 2**80 = Yi-
+
+#### BASE UNITS ####
+
+meter = [length] =  m = metre
+second = [time] = s = sec
+ampere = [current] = A = amp
+candela = [luminosity] = cd = candle
+gram = [mass] = g
+mole = [substance] = mol
+kelvin = [temperature]; offset: 0 = K = degK = °K = degree_Kelvin = degreeK  # older names supported for compatibility
+radian = [angle] = rad
+bit = [information]
+pixel = [digital_image_resolution] = px = pel
+
+#### NEXUS UNIT CATEGORIES ####
+[NX_ANGLE] = [angle]
+[NX_ANY] = []
+[NX_AREA] = [area]
+[NX_CHARGE] = [charge]
+[NX_COUNT] = []
+[NX_CROSS_SECTION] = [area]
+[NX_CURRENT] = [current]
+[NX_DIMENSIONLESS] = []
+[NX_EMITTANCE] = [length] * [angle]
+[NX_ENERGY] = [energy]
+[NX_FLUX] = 1 / [time] / [length] ** 2
+[NX_FREQUENCY] = [frequency]
+[NX_LENGTH] = [length]
+[NX_MASS] = [mass]
+[NX_MASS_DENSITY] = [mass] / [length] ** 3
+[NX_MOLECULAR_WEIGHT] = [mass] / [substance]
+[NX_PERIOD] = [time]
+[NX_PER_AREA] = 1 / [length] ** 2
+[NX_PER_LENGTH] = 1 / [length]
+[NX_POWER] = [power]
+[NX_PRESSURE] = [pressure]
+[NX_PULSES] = []
+[NX_SCATTERING_LENGTH_DENSITY] = 1 / [length] ** 2
+[NX_SOLID_ANGLE] = [angle] ** 2
+[NX_TEMPERATURE] = [temperature]
+[NX_TIME] = [time]
+[NX_TIME_OF_FLIGHT] = [time]
+[NX_UNITLESS] = []
+[NX_VOLTAGE] = [electric_potential]
+[NX_VOLUME] = [length] ** 3
+[NX_WAVELENGTH] = [length]
+[NX_WAVENUMBER] = [wavenumber]
+
+
+#### CONSTANTS ####
+
+@import constants_en.txt
+
+
+#### UNITS ####
+# Common and less common, grouped by quantity.
+# Conversion factors are exact (except when noted),
+# although floating-point conversion may introduce inaccuracies
+
+# Unitless
+counts = []
+
+# Angle
+degree = π / 180 * radian = ° = deg = arcdeg = arcdegree = angular_degree
+arcminute = degree / 60 = arcmin = arc_minute = angular_minute
+arcsecond = arcminute / 60 = arcsec = arc_second = angular_second
+milliarcsecond = 1e-3 * arcsecond = mas
+grade = π / 200 * radian = grad = gon
+mil = π / 32000 * radian
+
+# Solid angle
+steradian = radian ** 2 = sr
+square_degree = (π / 180) ** 2 * sr = sq_deg = sqdeg
+
+# Information
+byte = 8 * bit = B = octet
+baud = bit / second = Bd = bps
+
+# Length
+angstrom = 1e-10 * meter = Å = ångström = Å
+micron = micrometer = µ
+fermi = femtometer
+atomic_unit_of_length = h_bar / (alpha * m_e * c) = bohr = a_0 = a0 = bohr_radius = a_u_length
+planck_length = (h_bar * gravitational_constant / c ** 3) ** 0.5
+
+# Mass
+metric_ton = 1e3 * kilogram = tonne
+unified_atomic_mass_unit = atomic_mass_constant = u = amu
+dalton = atomic_mass_constant = Da
+grain = 64.79891 * milligram = gr
+gamma_mass = microgram
+carat = 200 * milligram = ct = karat
+planck_mass = (h_bar * c / gravitational_constant) ** 0.5
+
+# Time
+minute = 60 * second
+hour = 60 * minute = hr
+atomic_unit_of_time = h_bar / E_h = a_u_time
+planck_time = (h_bar * gravitational_constant / c ** 5) ** 0.5
+
+# Temperature
+degree_Celsius = kelvin; offset: 273.15 = °C = celsius = degC = degreeC
+degree_Rankine = 5 / 9 * kelvin; offset: 0 = °R = rankine = degR = degreeR
+degree_Fahrenheit = 5 / 9 * kelvin; offset: 233.15 + 200 / 9 = °F = fahrenheit = degF = degreeF
+degree_Reaumur = 4 / 5 * kelvin; offset: 273.15 = °Re = reaumur = degRe = degreeRe = degree_Réaumur = réaumur
+atomic_unit_of_temperature = E_h / k = a_u_temp
+planck_temperature = (h_bar * c ** 5 / gravitational_constant / k ** 2) ** 0.5
+
+# Area
+[area] = [length] ** 2
+barn = 1e-28 * meter ** 2 = b
+darcy = centipoise * centimeter ** 2 / (second * atmosphere)
+
+# Volume
+[volume] = [length] ** 3
+liter = decimeter ** 3 = l = L = litre
+lambda = microliter = λ
+
+# Frequency
+[frequency] = 1 / [time]
+hertz = 1 / second = Hz
+revolutions_per_minute = 1 / minute = rpm
+revolutions_per_second = 1 / second = rps
+counts_per_second = 1 / second = cps
+
+# Wavenumber
+[wavenumber] = 1 / [length]
+reciprocal_centimeter = 1 / cm = cm_1 = kayser
+
+# Speed
+[speed] = [length] / [time]
+mile_per_hour = mile / hour = mph = MPH
+kilometer_per_hour = kilometer / hour = kph = KPH
+kilometer_per_second = kilometer / second = kps
+meter_per_second = meter / second = mps
+foot_per_second = foot / second = fps
+
+# Acceleration
+[acceleration] = [speed] / [time]
+galileo = centimeter / second ** 2 = Gal
+
+# Force
+[force] = [mass] * [acceleration]
+newton = kilogram * meter / second ** 2 = N
+dyne = gram * centimeter / second ** 2 = dyn
+force_kilogram = g_0 * kilogram = pond
+force_gram = g_0 * gram = gf = gram_force
+force_metric_ton = g_0 * metric_ton = tf = metric_ton_force = force_t = t_force
+atomic_unit_of_force = E_h / a_0 = a_u_force
+
+# Energy
+[energy] = [force] * [length]
+joule = newton * meter = J
+erg = dyne * centimeter
+watt_hour = watt * hour = Wh = watthour
+electron_volt = e * volt = eV
+rydberg = h * c * R_inf = Ry
+hartree = 2 * rydberg = Ha = E_h = hartree_energy = atomic_unit_of_energy = a_u_energy
+calorie = 4.184 * joule = cal = thermochemical_calorie = cal_th
+international_calorie = 4.1868 * joule = cal_it = international_steam_table_calorie
+fifteen_degree_calorie = 4.1855 * joule = cal_15
+
+# Power
+[power] = [energy] / [time]
+watt = joule / second = W
+volt_ampere = volt * ampere = VA
+horsepower = 550 * foot * force_pound / second = hp = UK_horsepower = hydraulic_horsepower
+metric_horsepower = 75 * force_kilogram * meter / second
+electrical_horsepower = 746 * watt
+standard_liter_per_minute = atmosphere * liter / minute = slpm = slm
+conventional_watt_90 = K_J90 ** 2 * R_K90 / (K_J ** 2 * R_K) * watt = W_90
+
+# Momentum
+[momentum] = [length] * [mass] / [time]
+
+# Density (as auxiliary for pressure)
+[density] = [mass] / [volume]
+mercury = 13.5951 * kilogram / liter = Hg = Hg_0C = Hg_32F = conventional_mercury
+water = 1.0 * kilogram / liter = H2O = conventional_water
+mercury_60F = 13.5568 * kilogram / liter = Hg_60F   # approximate
+water_39F = 0.999972 * kilogram / liter = water_4C  # approximate
+water_60F = 0.999001 * kilogram / liter             # approximate
+
+# Pressure
+[pressure] = [force] / [area]
+pascal = newton / meter ** 2 = Pa
+barye = dyne / centimeter ** 2 = Ba = barie = barad = barrie = baryd
+bar = 1e5 * pascal
+torr = atm / 760
+pound_force_per_square_inch = force_pound / inch ** 2 = psi
+kip_per_square_inch = kip / inch ** 2 = ksi
+millimeter_Hg = millimeter * Hg * g_0 = mmHg = mm_Hg = millimeter_Hg_0C
+centimeter_Hg = centimeter * Hg * g_0 = cmHg = cm_Hg = centimeter_Hg_0C
+inch_Hg = inch * Hg * g_0 = inHg = in_Hg = inch_Hg_32F
+inch_Hg_60F = inch * Hg_60F * g_0
+inch_H2O_39F = inch * water_39F * g_0
+inch_H2O_60F = inch * water_60F * g_0
+foot_H2O = foot * water * g_0 = ftH2O = feet_H2O
+centimeter_H2O = centimeter * water * g_0 = cmH2O = cm_H2O
+atomic_unit_of_pressure = E_h / bohr_radius ** 3 = a_u_pressure
+
+# Viscosity
+[viscosity] = [pressure] * [time]
+poise = 0.1 * Pa * second = P
+reyn = psi * second
+
+# Kinematic viscosity
+[kinematic_viscosity] = [area] / [time]
+stokes = centimeter ** 2 / second = St
+
+# Fluidity
+[fluidity] = 1 / [viscosity]
+rhe = 1 / poise
+
+# Amount of substance
+particle = 1 / N_A = _ = molec = molecule
+
+# Concentration
+[concentration] = [substance] / [volume]
+molar = mole / liter = M
+
+# Catalytic activity
+[activity] = [substance] / [time]
+katal = mole / second = kat
+enzyme_unit = micromole / minute = U = enzymeunit
+
+# Entropy
+[entropy] = [energy] / [temperature]
+clausius = calorie / kelvin = Cl
+
+# Molar entropy
+[molar_entropy] = [entropy] / [substance]
+entropy_unit = calorie / kelvin / mole = eu
+
+# Radiation
+becquerel = counts_per_second = Bq
+curie = 3.7e10 * becquerel = Ci
+rutherford = 1e6 * becquerel = Rd
+gray = joule / kilogram = Gy
+sievert = joule / kilogram = Sv
+rem = 0.01 * sievert
+roentgen = 2.58e-4 * coulomb / kilogram = _ = röntgen  # approximate, depends on medium
+
+# Luminance
+[luminance] = [luminosity] / [area]
+nit = candela / meter ** 2
+stilb = candela / centimeter ** 2
+lambert = 1 / π * candela / centimeter ** 2
+
+# Luminous flux
+[luminous_flux] = [luminosity] * [angle] ** 2
+lumen = candela * steradian = lm
+
+# Illuminance
+[illuminance] = [luminous_flux] / [area]
+lux = lumen / meter ** 2 = lx
+
+# Intensity
+[intensity] = [power] / [area]
+atomic_unit_of_intensity = 0.5 * ε_0 * c * atomic_unit_of_electric_field ** 2 = a_u_intensity
+
+# Current
+biot = 10 * ampere = Bi
+abampere = biot = abA
+atomic_unit_of_current = e / atomic_unit_of_time = a_u_current
+mean_international_ampere = mean_international_volt / mean_international_ohm = A_it
+US_international_ampere = US_international_volt / US_international_ohm = A_US
+conventional_ampere_90 = K_J90 * R_K90 / (K_J * R_K) * ampere = A_90
+planck_current = (c ** 6 / gravitational_constant / k_C) ** 0.5
+
+# Charge
+[charge] = [current] * [time]
+coulomb = ampere * second = C
+abcoulomb = 10 * C = abC
+faraday = e * N_A * mole
+conventional_coulomb_90 = K_J90 * R_K90 / (K_J * R_K) * coulomb = C_90
+
+# Electric potential
+[electric_potential] = [energy] / [charge]
+volt = joule / coulomb = V
+abvolt = 1e-8 * volt = abV
+mean_international_volt = 1.00034 * volt = V_it  # approximate
+US_international_volt = 1.00033 * volt = V_US    # approximate
+conventional_volt_90 = K_J90 / K_J * volt = V_90
+
+# Electric field
+[electric_field] = [electric_potential] / [length]
+atomic_unit_of_electric_field = e * k_C / a_0 ** 2 = a_u_electric_field
+
+# Electric displacement field
+[electric_displacement_field] = [charge] / [area]
+
+# Resistance
+[resistance] = [electric_potential] / [current]
+ohm = volt / ampere = Ω
+abohm = 1e-9 * ohm = abΩ
+mean_international_ohm = 1.00049 * ohm = Ω_it = ohm_it  # approximate
+US_international_ohm = 1.000495 * ohm = Ω_US = ohm_US   # approximate
+conventional_ohm_90 = R_K / R_K90 * ohm = Ω_90 = ohm_90
+
+# Resistivity
+[resistivity] = [resistance] * [length]
+
+# Conductance
+[conductance] = [current] / [electric_potential]
+siemens = ampere / volt = S = mho
+absiemens = 1e9 * siemens = abS = abmho
+
+# Capacitance
+[capacitance] = [charge] / [electric_potential]
+farad = coulomb / volt = F
+abfarad = 1e9 * farad = abF
+conventional_farad_90 = R_K90 / R_K * farad = F_90
+
+# Inductance
+[inductance] = [magnetic_flux] / [current]
+henry = weber / ampere = H
+abhenry = 1e-9 * henry = abH
+conventional_henry_90 = R_K / R_K90 * henry = H_90
+
+# Magnetic flux
+[magnetic_flux] = [electric_potential] * [time]
+weber = volt * second = Wb
+unit_pole = µ_0 * biot * centimeter
+
+# Magnetic field
+[magnetic_field] = [magnetic_flux] / [area]
+tesla = weber / meter ** 2 = T
+gamma = 1e-9 * tesla = γ
+gauss = 1e-4 * tesla = G
+
+# Magnetic field strength
+[magnetic_field_strength] = [current] / [length]
+
+# Electric dipole moment
+[electric_dipole] = [charge] * [length]
+debye = 1e-9 / ζ * coulomb * angstrom = D  # formally 1 D = 1e-10 Fr*Å, but we generally want to use it outside the Gaussian context
+
+# Electric quadrupole moment
+[electric_quadrupole] = [charge] * [area]
+buckingham = debye * angstrom
+
+# Magnetic dipole moment
+[magnetic_dipole] = [current] * [area]
+bohr_magneton = e * h_bar / (2 * m_e) = µ_B = mu_B
+nuclear_magneton = e * h_bar / (2 * m_p) = µ_N = mu_N
+
+# Pixel density
+[pixel_density] = [digital_image_resolution] / [length]
+pixels_per_inch = px / inch = PPI = ppi
+pixels_per_centimeter = px / cm = PPCM = ppcm
+
+#### UNIT GROUPS ####
+# Mostly for length, area, volume, mass, force
+# (customary or specialized units)
+
+@group USCSLengthInternational
+    thou = 1e-3 * inch = th = mil_length
+    inch = yard / 36 = in = international_inch = inches = international_inches
+    hand = 4 * inch
+    foot = yard / 3 = ft = international_foot = feet = international_feet
+    yard = 0.9144 * meter = yd = international_yard  # since Jul 1959
+    mile = 1760 * yard = mi = international_mile
+
+    square_inch = inch ** 2 = sq_in = square_inches
+    square_foot = foot ** 2 = sq_ft = square_feet
+    square_yard = yard ** 2 = sq_yd
+    square_mile = mile ** 2 = sq_mi
+
+    cubic_inch = in ** 3 = cu_in
+    cubic_foot = ft ** 3 = cu_ft = cubic_feet
+    cubic_yard = yd ** 3 = cu_yd
+@end
+
+@group USCSLengthSurvey
+    link = 1e-2 * chain = li = survey_link
+    survey_foot = 1200 / 3937 * meter = sft
+    fathom = 6 * survey_foot
+    rod = 16.5 * survey_foot = rd = pole = perch
+    chain = 4 * rod
+    furlong = 40 * rod = fur
+    cables_length = 120 * fathom
+    survey_mile = 5280 * survey_foot = smi = us_statute_mile
+    league = 3 * survey_mile
+
+    square_rod = rod ** 2 = sq_rod = sq_pole = sq_perch
+    acre = 10 * chain ** 2
+    square_survey_mile = survey_mile ** 2 = _ = section
+    square_league = league ** 2
+
+    acre_foot = acre * survey_foot = _ = acre_feet
+@end
+
+@group USCSLiquidVolume
+    minim = pint / 7680
+    fluid_dram = pint / 128 = fldr = fluidram = US_fluid_dram = US_liquid_dram
+    fluid_ounce = pint / 16 = floz = US_fluid_ounce = US_liquid_ounce
+    gill = pint / 4 = gi = liquid_gill = US_liquid_gill
+    pint = quart / 2 = liquid_pint = US_pint
+    fifth = gallon / 5 = _ = US_liquid_fifth
+    quart = gallon / 4 = qt = liquid_quart = US_liquid_quart
+    gallon = 231 * cubic_inch = gal = liquid_gallon = US_liquid_gallon
+@end
+
+@group Avoirdupois
+    dram = pound / 256 = dr = avoirdupois_dram = avdp_dram = drachm
+    ounce = pound / 16 = oz = avoirdupois_ounce = avdp_ounce
+    pound = 7e3 * grain = lb = avoirdupois_pound = avdp_pound
+    stone = 14 * pound
+    quarter = 28 * stone
+    bag = 94 * pound
+    hundredweight = 100 * pound = cwt = short_hundredweight
+    long_hundredweight = 112 * pound
+    ton = 2e3 * pound = _ = short_ton
+    long_ton = 2240 * pound
+    slug = g_0 * pound * second ** 2 / foot
+    slinch = g_0 * pound * second ** 2 / inch = blob = slugette
+
+    force_ounce = g_0 * ounce = ozf = ounce_force
+    force_pound = g_0 * pound = lbf = pound_force
+    force_ton = g_0 * ton = _ = ton_force = force_short_ton = short_ton_force
+    force_long_ton = g_0 * long_ton = _ = long_ton_force
+    kip = 1e3 * force_pound
+    poundal = pound * foot / second ** 2 = pdl
+@end
+
+@group AvoirdupoisUK using Avoirdupois
+    UK_hundredweight = long_hundredweight = UK_cwt
+    UK_ton = long_ton
+    UK_force_ton = force_long_ton = _ = UK_ton_force
+@end
+
+@group AvoirdupoisUS using Avoirdupois
+    US_hundredweight = hundredweight = US_cwt
+    US_ton = ton
+    US_force_ton = force_ton = _ = US_ton_force
+@end
+
+@group Troy
+    pennyweight = 24 * grain = dwt
+    troy_ounce = 480 * grain = toz = ozt
+    troy_pound = 12 * troy_ounce = tlb = lbt
+@end
+
+@group ImperialVolume
+    imperial_minim = imperial_fluid_ounce / 480
+    imperial_fluid_scruple = imperial_fluid_ounce / 24
+    imperial_fluid_drachm = imperial_fluid_ounce / 8 = imperial_fldr = imperial_fluid_dram
+    imperial_fluid_ounce = imperial_pint / 20 = imperial_floz = UK_fluid_ounce
+    imperial_gill = imperial_pint / 4 = imperial_gi = UK_gill
+    imperial_cup = imperial_pint / 2 = imperial_cp = UK_cup
+    imperial_pint = imperial_gallon / 8 = imperial_pt = UK_pint
+    imperial_quart = imperial_gallon / 4 = imperial_qt = UK_quart
+    imperial_gallon = 4.54609 * liter = imperial_gal = UK_gallon
+    imperial_peck = 2 * imperial_gallon = imperial_pk = UK_pk
+    imperial_bushel = 8 * imperial_gallon = imperial_bu = UK_bushel
+    imperial_barrel = 36 * imperial_gallon = imperial_bbl = UK_bbl
+@end
+
+
+#### CONVERSION CONTEXTS ####
+
+@context(n=1) spectroscopy = sp
+    # n index of refraction of the medium.
+    [length] <-> [frequency]: speed_of_light / n / value
+    [frequency] -> [energy]: planck_constant * value
+    [energy] -> [frequency]: value / planck_constant
+    # allow wavenumber / kayser
+    [wavenumber] <-> [length]: 1 / value
+@end
+
+@context boltzmann
+    [temperature] -> [energy]: boltzmann_constant * value
+    [energy] -> [temperature]: value / boltzmann_constant
+@end
+
+@context energy
+    [energy] -> [energy] / [substance]: value * N_A
+    [energy] / [substance] -> [energy]: value / N_A
+    [energy] -> [mass]: value / c ** 2
+    [mass] -> [energy]: value * c ** 2
+@end
+
+@context(mw=0,volume=0,solvent_mass=0) chemistry = chem
+    # mw is the molecular weight of the species
+    # volume is the volume of the solution
+    # solvent_mass is the mass of solvent in the solution
+
+    # moles -> mass require the molecular weight
+    [substance] -> [mass]: value * mw
+    [mass] -> [substance]: value / mw
+
+    # moles/volume -> mass/volume and moles/mass -> mass/mass
+    # require the  molecular weight
+    [substance] / [volume] -> [mass] / [volume]: value * mw
+    [mass] / [volume] -> [substance] / [volume]: value / mw
+    [substance] / [mass] -> [mass] / [mass]: value * mw
+    [mass] / [mass] -> [substance] / [mass]: value / mw
+
+    # moles/volume -> moles requires the solution volume
+    [substance] / [volume] -> [substance]: value * volume
+    [substance] -> [substance] / [volume]: value / volume
+
+    # moles/mass -> moles requires the solvent (usually water) mass
+    [substance] / [mass] -> [substance]: value * solvent_mass
+    [substance] -> [substance] / [mass]: value / solvent_mass
+
+    # moles/mass -> moles/volume require the solvent mass and the volume
+    [substance] / [mass] -> [substance]/[volume]: value * solvent_mass / volume
+    [substance] / [volume] -> [substance] / [mass]: value / solvent_mass * volume
+
+@end
+
+
+#### SYSTEMS OF UNITS ####
+
+@system SI
+    second
+    meter
+    kilogram
+    ampere
+    kelvin
+    mole
+    candela
+@end
+
+@system mks using international
+    meter
+    kilogram
+    second
+@end
+
+@system atomic using international
+    # based on unit m_e, e, h_bar, k_C, k
+    bohr: meter
+    electron_mass: gram
+    atomic_unit_of_time: second
+    atomic_unit_of_current: ampere
+    atomic_unit_of_temperature: kelvin
+@end
\ No newline at end of file
diff --git a/src/pynxtools/dataconverter/validation.py b/src/pynxtools/dataconverter/validation.py
index 63a715f6a..7e03cf1ae 100644
--- a/src/pynxtools/dataconverter/validation.py
+++ b/src/pynxtools/dataconverter/validation.py
@@ -20,11 +20,13 @@
 from collections import defaultdict
 from functools import reduce
 from operator import getitem
-from typing import Any, Iterable, List, Mapping, Optional, Tuple, Union
+from typing import Any, Iterable, List, Mapping, Optional, Set, Tuple, Union
 
 import h5py
 import lxml.etree as ET
 import numpy as np
+from cachetools import LRUCache, cached
+from cachetools.keys import hashkey
 
 from pynxtools.dataconverter.helpers import (
     Collector,
@@ -32,6 +34,7 @@
     collector,
     convert_nexus_to_caps,
     is_valid_data_field,
+    is_valid_unit,
 )
 from pynxtools.dataconverter.nexus_tree import (
     NexusEntity,
@@ -42,19 +45,145 @@
 from pynxtools.definitions.dev_tools.utils.nxdl_utils import get_nx_namefit
 
 
-def validate_hdf_group_against(appdef: str, data: h5py.Group):
+def best_namefit_of_(name: str, concepts: Set[str]) -> str:
+    if not concepts:
+        return None
+
+    if name in concepts:
+        return name
+
+    best_match, score = max(
+        map(lambda x: (x, get_nx_namefit(name, x)), concepts), key=lambda x: x[1]
+    )
+    if score < 0:
+        return None
+
+    return best_match
+
+
+def validate_hdf_group_against(appdef: str, data: h5py.Group) -> bool:
     """
-    Checks whether all the required paths from the template are returned in data dict.
+    Validate an HDF5 group against the Nexus tree for the application definition `appdef`.
 
-    THIS IS JUST A FUNCTION SKELETON AND IS NOT WORKING YET!
+    Args:
+        appdef (str): The application definition to validate against.
+        data (h5py.Group): The h5py group to validate.
+
+    Returns:
+        bool: True if the group is valid according to `appdef`, False otherwise.
     """
 
-    def validate(name: str, data: Union[h5py.Group, h5py.Dataset]):
+    # Only cache based on path. That way we retain the nx_class information
+    # in the tree
+    # Allow for 10000 cache entries. This should be enough for most cases
+    @cached(
+        cache=LRUCache(maxsize=10000),
+        key=lambda path, node_type=None, nx_class=None: hashkey(path),
+    )
+    def find_node_for(
+        path: str, node_type: Optional[str] = None, nx_class: Optional[str] = None
+    ) -> Optional[NexusNode]:
+        if path == "":
+            return tree
+
+        *prev_path, last_elem = path.rsplit("/", 1)
+        node = find_node_for(prev_path[0]) if prev_path else tree
+
+        if node is None:
+            return None
+
+        best_child = best_namefit_of_(
+            last_elem,
+            node.get_all_direct_children_names(nx_class=nx_class, node_type=node_type),
+        )
+        if best_child is None:
+            return None
+
+        return node.search_add_child_for(best_child)
+
+    def remove_from_req_fields(path: str):
+        if path in required_fields:
+            required_fields.remove(path)
+
+    def handle_group(path: str, data: h5py.Group):
+        node = find_node_for(
+            path, node_type="group", nx_class=data.attrs.get("NX_class")
+        )
+        if node is None:
+            collector.collect_and_log(
+                path, ValidationProblem.MissingDocumentation, None
+            )
+            return
+
+        # TODO: Do actual group checks
+
+    def handle_field(path: str, data: h5py.Dataset):
+        node = find_node_for(path, node_type="field")
+        if node is None:
+            collector.collect_and_log(
+                path, ValidationProblem.MissingDocumentation, None
+            )
+            return
+        remove_from_req_fields(node.get_path())
+        is_valid_data_field(data[()], node.dtype, path)
+
+        units = data.attrs.get("units")
+        if node.unit is not None:
+            if units is None:
+                collector.collect_and_log(
+                    f"{path}/@units", ValidationProblem.MissingUnit, node.unit
+                )
+                return
+            remove_from_req_fields(f"{node.get_path()}/@units")
+            is_valid_unit(units, node.unit, None)
+        elif units is not None:
+            collector.collect_and_log(
+                f"{entry_name}/{path}/@units",
+                ValidationProblem.MissingDocumentation,
+                path,
+            )
+
+    def handle_attributes(path: str, attrs: h5py.AttributeManager):
+        for attr_name in attrs:
+            if attr_name in ("NX_class", "units"):
+                # Ignore special attrs
+                continue
+
+            node = find_node_for(f"{path}/{attr_name}", node_type="attribute")
+            if node is None:
+                collector.collect_and_log(
+                    f"{path}/@{attr_name}", ValidationProblem.MissingDocumentation, None
+                )
+                continue
+            remove_from_req_fields(node.get_path())
+            is_valid_data_field(attrs.get(attr_name), node.dtype, node.get_path())
+
+    def validate(path: str, data: Union[h5py.Group, h5py.Dataset]):
         # Namefit name against tree (use recursive caching)
-        pass
+        if isinstance(data, h5py.Group):
+            handle_group(path, data)
+        elif isinstance(data, h5py.Dataset):
+            handle_field(path, data)
 
-    tree = generate_tree_from(appdef)
-    data.visitems(validate)
+        handle_attributes(path, data.attrs)
+
+    appdef = generate_tree_from(appdef)
+    required_fields = appdef.required_fields_and_attrs_names()
+    tree = appdef.search_add_child_for("ENTRY")
+    entry_name = data.name
+    data.visititems(validate)
+
+    for req_field in required_fields:
+        if "@" in req_field:
+            collector.collect_and_log(
+                req_field, ValidationProblem.MissingRequiredAttribute, None
+            )
+            continue
+        collector.collect_and_log(
+            req_field, ValidationProblem.MissingRequiredField, None
+        )
+
+    return not collector.has_validation_problems()
 
 
 def build_nested_dict_from(
@@ -174,7 +303,7 @@ def validate_dict_against(
         appdef (str): The appdef name to validate against.
         mapping (Mapping[str, Any]):
             The mapping containing the data to validate.
-            This should be a dict of `/` separated paths.
+            This should be a dict of `/` separated paths elements.
             Attributes are denoted with `@` in front of the last element.
         ignore_undocumented (bool, optional):
             Ignore all undocumented keys in the verification
diff --git a/src/pynxtools/dataconverter/verify.py b/src/pynxtools/dataconverter/verify.py
new file mode 100644
index 000000000..dd2a3c5a1
--- /dev/null
+++ b/src/pynxtools/dataconverter/verify.py
@@ -0,0 +1,84 @@
+#
+# Copyright The NOMAD Authors.
+#
+# This file is part of NOMAD. See https://nomad-lab.eu for further info.
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#     http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""Verifies a nxs file"""
+
+import logging
+import os
+import sys
+import xml.etree.ElementTree as ET
+from os import path
+from typing import Dict, Union
+
+import click
+from h5py import File, is_hdf5
+
+from pynxtools.dataconverter import helpers
+from pynxtools.dataconverter.validation import validate_hdf_group_against
+
+logger = logging.getLogger(__name__)
+logger.setLevel(logging.INFO)
+
+
+def _get_def_map(file: str) -> Dict[str, str]:
+    def_map: Dict[str, str] = {}
+    with File(file, "r") as h5file:
+        for entry_name, dataset in h5file.items():
+            if (
+                helpers.clean_str_attr(dataset.attrs.get("NX_class")) == "NXentry"
+                and f"/{entry_name}/definition" in h5file
+            ):
+                def_map.update(
+                    {entry_name: h5file[f"/{entry_name}/definition"][()].decode("utf8")}
+                )
+
+    return def_map
+
+
+@click.command()
+@click.argument("file")
+def verify(file: str):
+    """Verifies a nexus file"""
+
+    if not path.exists(file):
+        raise click.FileError(file, hint=f'File "{file}" does not exist.')
+
+    if not path.isfile(file):
+        raise click.FileError(file, hint=f'"{file}" is not a file.')
+
+    if not is_hdf5(file):
+        raise click.FileError(file, hint=f'"{file}" is not a valid HDF5 file.')
+
+    def_map = _get_def_map(file)
+
+    if not def_map:
+        logger.info(f"Could not find any valid entry in file {file}")
+
+    with File(file, "r") as h5file:
+        for entry, nxdl in def_map.items():
+            is_valid = validate_hdf_group_against(nxdl, h5file[entry])
+
+            if is_valid:
+                logger.info(
+                    f"The entry `{entry}` in file `{file}` is a valid file"
+                    f" according to the `{nxdl}` application definition.",
+                )
+            else:
+                logger.info(
+                    f"Invalid: The entry `{entry}` in file `{file}` is NOT a valid file"
+                    f" according to the `{nxdl}` application definition.",
+                )
diff --git a/src/pynxtools/definitions b/src/pynxtools/definitions
index f75a29836..40a2e8ad5 160000
--- a/src/pynxtools/definitions
+++ b/src/pynxtools/definitions
@@ -1 +1 @@
-Subproject commit f75a29836431f35d68df6174e3868a0418523397
+Subproject commit 40a2e8ad57facb6f16839ef47c4d3eedcc2e4b37
diff --git a/tests/dataconverter/test_helpers.py b/tests/dataconverter/test_helpers.py
index ddbcb2351..84eb61506 100644
--- a/tests/dataconverter/test_helpers.py
+++ b/tests/dataconverter/test_helpers.py
@@ -336,11 +336,7 @@ def fixture_filled_test_data(template, tmp_path):
                 "/ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value",
                 "required",
             ),
-            (
-                "The data entry corresponding to /ENTRY[my_entry]/NXODD_name[nxodd_name]"
-                "/bool_value is"
-                " required and hasn't been supplied by the reader."
-            ),
+            "Missing field: /ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value",
             id="empty-required-field",
         ),
         pytest.param(
@@ -349,11 +345,7 @@ def fixture_filled_test_data(template, tmp_path):
                 "/ENTRY[my_entry]/NXODD_name[nxodd_two_name]/bool_value",
                 "required",
             ),
-            (
-                "The data entry corresponding to /ENTRY[my_entry]/"
-                "NXODD_name[nxodd_two_name]/bool_value is"
-                " required and hasn't been supplied by the reader."
-            ),
+            "Missing field: /ENTRY[my_entry]/NXODD_name[nxodd_two_name]/bool_value",
             id="empty-required-field",
         ),
         pytest.param(
@@ -366,11 +358,7 @@ def fixture_filled_test_data(template, tmp_path):
                 "/ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value",
                 "required",
             ),
-            (
-                "The data entry corresponding to /ENTRY[my_entry]/NXODD_name[nxodd_name]"
-                "/bool_value is"
-                " required and hasn't been supplied by the reader."
-            ),
+            "Missing field: /ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value",
             id="empty-required-field",
         ),
         pytest.param(
@@ -432,10 +420,7 @@ def fixture_filled_test_data(template, tmp_path):
             set_to_none_in_dict(
                 TEMPLATE, "/ENTRY[my_entry]/optional_parent/required_child", "optional"
             ),
-            (
-                "The data entry corresponding to /ENTRY[my_entry]/optional_parent/"
-                "required_child is required and hasn't been supplied by the reader."
-            ),
+            "Missing field: /ENTRY[my_entry]/optional_parent/required_child",
             id="atleast-one-required-child-not-provided-optional-parent",
         ),
         pytest.param(
@@ -444,11 +429,7 @@ def fixture_filled_test_data(template, tmp_path):
                 "/ENTRY[my_entry]/OPTIONAL_group[my_group]/required_field",
                 "required",
             ),
-            (
-                "The data entry corresponding to /ENTRY[my_entry]/"
-                "OPTIONAL_group[my_group]/required_field "
-                "is required and hasn't been supplied by the reader."
-            ),
+            "Missing field: /ENTRY[my_entry]/OPTIONAL_group[my_group]/required_field",
             id="required-field-not-provided-in-variadic-optional-group",
         ),
         pytest.param(
diff --git a/tests/dataconverter/test_validation.py b/tests/dataconverter/test_validation.py
index 135d0476c..a8dde5ffa 100644
--- a/tests/dataconverter/test_validation.py
+++ b/tests/dataconverter/test_validation.py
@@ -17,11 +17,17 @@
 # limitations under the License.
 #
 import logging
+import os
 from typing import Any, Dict, List, Tuple, Union
 
 import numpy as np
 import pytest
+from click.testing import CliRunner
+from pynxtools.dataconverter.helpers import get_nxdl_root_and_path
+from pynxtools.dataconverter.template import Template
 from pynxtools.dataconverter.validation import validate_dict_against
+from pynxtools.dataconverter.verify import verify
+from pynxtools.dataconverter.writer import Writer
 
 
 def get_data_dict():
@@ -109,7 +115,7 @@ def test_valid_data_dict(caplog, data_dict):
             remove_from_dict(
                 "/ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value", get_data_dict()
             ),
-            "The data entry corresponding to /ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value is required and hasn't been supplied by the reader.",
+            "Missing field: /ENTRY[my_entry]/NXODD_name[nxodd_name]/bool_value",
             id="missing-required-value",
         )
     ],
@@ -119,3 +125,68 @@ def test_validation_shows_warning(caplog, data_dict, error_message):
         assert not validate_dict_against("NXtest", data_dict)
 
     assert error_message in caplog.text
+
+
+data_dict_list = [
+    (
+        {
+            "/ENTRY[entry]/definition": "NXhdf5_validator_2",
+            "/ENTRY[entry]/version": "no version",
+            "/ENTRY[entry]/experiment_result/hdf5_validator_2_intensity": np.array(
+                [[11, 12, 13], [21, 22, 23]]
+            ),
+            "/ENTRY[entry]/hdf5_validator_1_program_name": "hdf5_file_validator",
+            "/ENTRY[entry]/hdf5_validator_1_required/required_field": "Required_field_from nxdl-1",
+            "/ENTRY[entry]/hdf5_validator_2_users_req/required_field": "Required_field_from_nxdl-2",
+        },
+        {
+            "error_messages": [
+                "WARNING: Field version written without documentation.",
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/@long_name"',
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/@AXISNAME_indices"',
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/@axes"',
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/@auxiliary_signals"',
+                "WARNING: Missing field: /ENTRY/experiment_result/DATA",
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/DATA/@units"',
+                "WARNING: Missing field: /ENTRY/experiment_result/AXISNAME",
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/AXISNAME/@units"',
+                'WARNING: Missing attribute: "/ENTRY/experiment_result/@signal"',
+                'WARNING: Missing attribute: "/ENTRY/definition/@version"',
+                "is NOT a valid file according to the `NXhdf5_validator_2` application definition.",
+            ]
+        },
+    ),
+    ({}, {}),
+]
+
+
+@pytest.mark.parametrize("data_dict, error_massages", data_dict_list)
+def test_nexus_file_validate(data_dict, error_massages, tmp_path, caplog):
+    if not data_dict and not error_massages:
+        return
+
+    caplog_level = "INFO"
+    template = Template()
+
+    for key, val in data_dict.items():
+        template[key] = val
+
+    nxdl_name = "NXhdf5_validator_2"
+    _, nxdl_path = get_nxdl_root_and_path(nxdl=nxdl_name)
+    hdf_file_path = tmp_path / "hdf5_validator_test.nxs"
+    Writer(data=template, nxdl_f_path=nxdl_path, output_path=hdf_file_path).write()
+    with caplog.at_level(caplog_level):
+        _ = CliRunner().invoke(verify, [str(hdf_file_path)])
+    error_massages = error_massages["error_messages"]
+    for record in caplog.records:
+        try:
+            assert (
+                record.msg in error_massages
+            ), f"Error message not found: {record.msg}"
+        except AssertionError:
+            # Only for detecting entry or missing application definition massage
+            assert (
+                error_massages[-1] in record.msg
+            ), f"Error message not found: {record.msg}"
+
+    os.remove(hdf_file_path)