diff --git a/CHANGES.md b/CHANGES.md
index 36b5ad6..840b0b1 100644
--- a/CHANGES.md
+++ b/CHANGES.md
@@ -5,12 +5,12 @@
 ### Adjustments and Enhancements
 
 - Added a new core rule `access-latency` that can be used to check the
-  time it takes to open datasets.
+  time it takes to open a dataset.
 
 - Added HTML styling for both CLI output (`--format html`) and rendering
   of `Result` objects in Jupyter notebooks.
 
-- Rule `no-empty-chunks` has taken off the `"recommended"` settings 
+- Rule `no-empty-chunks` has been taken off the `"recommended"` settings 
   as there is no easy/efficient way to tell whether a dataset has 
   been written using `write_emtpy_chunks` option or not.
   The rule message itself has been fixed. (#45) 
@@ -19,8 +19,9 @@
   to be consistent with messages of other rules.
 
 - Core rule `dataset-title-attr` has been moved into `xcube` plugin
-  and renamed to `xcube/dataset-title` because the core rule `var-descr` 
-  covers checking for dataset titles.
+  and renamed to `xcube/dataset-title` because the core rule 
+  `content-desc` covers checking for dataset titles and other descriptive 
+  attributes.
 
 ### Incompatible API changes
 
@@ -49,6 +50,7 @@
 - XRLint now works with zarr >=2,<3 and zarr >=3.0.2
 - Added more tests so we finally reached 100% coverage.
 - New `PluginMeta.docs_url` property.
+- Inserted copyright header into all source files.
 
 ## Version 0.4.1 (from 2025-01-31)
 
diff --git a/examples/__init__.py b/examples/__init__.py
index e69de29..f0b6197 100644
--- a/examples/__init__.py
+++ b/examples/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/examples/check_s3_bucket.py b/examples/check_s3_bucket.py
index 083b093..6aada6f 100644
--- a/examples/check_s3_bucket.py
+++ b/examples/check_s3_bucket.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xrlint.all as xrl
 
 URL = "s3://xcube-test/"
diff --git a/examples/plugin_config.py b/examples/plugin_config.py
index 5059f22..1981446 100644
--- a/examples/plugin_config.py
+++ b/examples/plugin_config.py
@@ -3,6 +3,10 @@
 using the `Plugin` class and its `define_rule()` decorator method.
 """
 
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugin import new_plugin
 from xrlint.rule import RuleContext, RuleOp
diff --git a/examples/rule_testing.py b/examples/rule_testing.py
index e6351f5..52c0369 100644
--- a/examples/rule_testing.py
+++ b/examples/rule_testing.py
@@ -2,6 +2,10 @@
 This example demonstrates how to develop new rules.
 """
 
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.node import DatasetNode
diff --git a/examples/virtual_plugin_config.py b/examples/virtual_plugin_config.py
index 9840150..5845d88 100644
--- a/examples/virtual_plugin_config.py
+++ b/examples/virtual_plugin_config.py
@@ -4,6 +4,10 @@
 can be defined inside a configuration item.
 """
 
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.rule import RuleContext, RuleOp, define_rule
 
diff --git a/mkruleref.py b/mkruleref.py
index 2050bed..4b5a36c 100644
--- a/mkruleref.py
+++ b/mkruleref.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.plugin import Plugin
 from xrlint.rule import RuleConfig
 
diff --git a/notebooks/mkdataset.py b/notebooks/mkdataset.py
index ebc9998..63e8b51 100644
--- a/notebooks/mkdataset.py
+++ b/notebooks/mkdataset.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/__init__.py b/tests/__init__.py
index e69de29..f0b6197 100644
--- a/tests/__init__.py
+++ b/tests/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/_linter/__init__.py b/tests/_linter/__init__.py
index e69de29..f0b6197 100644
--- a/tests/_linter/__init__.py
+++ b/tests/_linter/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/_linter/test_rulectx.py b/tests/_linter/test_rulectx.py
index 0eb6092..58102ef 100644
--- a/tests/_linter/test_rulectx.py
+++ b/tests/_linter/test_rulectx.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 import xarray as xr
diff --git a/tests/cli/__init__.py b/tests/cli/__init__.py
index e69de29..f0b6197 100644
--- a/tests/cli/__init__.py
+++ b/tests/cli/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/cli/configs/recommended.py b/tests/cli/configs/recommended.py
index dc5615a..45439fe 100644
--- a/tests/cli/configs/recommended.py
+++ b/tests/cli/configs/recommended.py
@@ -1,3 +1,8 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
+
 def export_config():
     import xrlint.plugins.core
     import xrlint.plugins.xcube
diff --git a/tests/cli/helpers.py b/tests/cli/helpers.py
index 502deae..78a7b8a 100644
--- a/tests/cli/helpers.py
+++ b/tests/cli/helpers.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import os
 from contextlib import contextmanager
 
diff --git a/tests/cli/test_config.py b/tests/cli/test_config.py
index 58db008..c40dab1 100644
--- a/tests/cli/test_config.py
+++ b/tests/cli/test_config.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import unittest
 from pathlib import Path
 from typing import Any
diff --git a/tests/cli/test_main.py b/tests/cli/test_main.py
index 09f658c..4f2898c 100644
--- a/tests/cli/test_main.py
+++ b/tests/cli/test_main.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import os
 import shutil
 import tempfile
diff --git a/tests/formatters/__init__.py b/tests/formatters/__init__.py
index e69de29..f0b6197 100644
--- a/tests/formatters/__init__.py
+++ b/tests/formatters/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/formatters/helpers.py b/tests/formatters/helpers.py
index 32f72cb..70c46ef 100644
--- a/tests/formatters/helpers.py
+++ b/tests/formatters/helpers.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.config import ConfigObject
 from xrlint.formatter import FormatterContext
 from xrlint.plugin import new_plugin
diff --git a/tests/formatters/test_html.py b/tests/formatters/test_html.py
index e11ccf9..3ea21e0 100644
--- a/tests/formatters/test_html.py
+++ b/tests/formatters/test_html.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.formatters.html import Html, HtmlText
diff --git a/tests/formatters/test_json.py b/tests/formatters/test_json.py
index c108be5..2f1a2bc 100644
--- a/tests/formatters/test_json.py
+++ b/tests/formatters/test_json.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.formatters.json import Json
diff --git a/tests/formatters/test_simple.py b/tests/formatters/test_simple.py
index 8bc13eb..70e9e07 100644
--- a/tests/formatters/test_simple.py
+++ b/tests/formatters/test_simple.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from tests.formatters.helpers import get_context
diff --git a/tests/plugins/__init__.py b/tests/plugins/__init__.py
index e69de29..f0b6197 100644
--- a/tests/plugins/__init__.py
+++ b/tests/plugins/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/plugins/core/__init__.py b/tests/plugins/core/__init__.py
index e69de29..f0b6197 100644
--- a/tests/plugins/core/__init__.py
+++ b/tests/plugins/core/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/plugins/core/rules/__init__.py b/tests/plugins/core/rules/__init__.py
index e69de29..f0b6197 100644
--- a/tests/plugins/core/rules/__init__.py
+++ b/tests/plugins/core/rules/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/plugins/core/rules/test_access_latency.py b/tests/plugins/core/rules/test_access_latency.py
index 67315a5..57b9231 100644
--- a/tests/plugins/core/rules/test_access_latency.py
+++ b/tests/plugins/core/rules/test_access_latency.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 import pytest
diff --git a/tests/plugins/core/rules/test_content_desc.py b/tests/plugins/core/rules/test_content_desc.py
index 10806b0..f0d2119 100644
--- a/tests/plugins/core/rules/test_content_desc.py
+++ b/tests/plugins/core/rules/test_content_desc.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.content_desc import ContentDesc
diff --git a/tests/plugins/core/rules/test_conventions.py b/tests/plugins/core/rules/test_conventions.py
index 0fb214b..8472eef 100644
--- a/tests/plugins/core/rules/test_conventions.py
+++ b/tests/plugins/core/rules/test_conventions.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.conventions import Conventions
diff --git a/tests/plugins/core/rules/test_coords_for_dims.py b/tests/plugins/core/rules/test_coords_for_dims.py
index 18292fa..306efba 100644
--- a/tests/plugins/core/rules/test_coords_for_dims.py
+++ b/tests/plugins/core/rules/test_coords_for_dims.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.coords_for_dims import CoordsForDims
diff --git a/tests/plugins/core/rules/test_grid_mappings.py b/tests/plugins/core/rules/test_grid_mappings.py
index 2ba9be6..13252ab 100644
--- a/tests/plugins/core/rules/test_grid_mappings.py
+++ b/tests/plugins/core/rules/test_grid_mappings.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/core/rules/test_lat_lon_coordinate.py b/tests/plugins/core/rules/test_lat_lon_coordinate.py
index ab93f70..18a2286 100644
--- a/tests/plugins/core/rules/test_lat_lon_coordinate.py
+++ b/tests/plugins/core/rules/test_lat_lon_coordinate.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/core/rules/test_no_empty_attrs.py b/tests/plugins/core/rules/test_no_empty_attrs.py
index 62ecd7e..6ea92b0 100644
--- a/tests/plugins/core/rules/test_no_empty_attrs.py
+++ b/tests/plugins/core/rules/test_no_empty_attrs.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.no_empty_attrs import NoEmptyAttrs
diff --git a/tests/plugins/core/rules/test_no_empty_chunks.py b/tests/plugins/core/rules/test_no_empty_chunks.py
index 9f0db7c..49a98e9 100644
--- a/tests/plugins/core/rules/test_no_empty_chunks.py
+++ b/tests/plugins/core/rules/test_no_empty_chunks.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.no_empty_chunks import NoEmptyChunks
diff --git a/tests/plugins/core/rules/test_time_coordinate.py b/tests/plugins/core/rules/test_time_coordinate.py
index 44e278b..94b233f 100644
--- a/tests/plugins/core/rules/test_time_coordinate.py
+++ b/tests/plugins/core/rules/test_time_coordinate.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/core/rules/test_var_desc.py b/tests/plugins/core/rules/test_var_desc.py
index 362b8c0..69234de 100644
--- a/tests/plugins/core/rules/test_var_desc.py
+++ b/tests/plugins/core/rules/test_var_desc.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.var_desc import VarDesc
diff --git a/tests/plugins/core/rules/test_var_flags.py b/tests/plugins/core/rules/test_var_flags.py
index 95e8622..a3b12cc 100644
--- a/tests/plugins/core/rules/test_var_flags.py
+++ b/tests/plugins/core/rules/test_var_flags.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/core/rules/test_var_units.py b/tests/plugins/core/rules/test_var_units.py
index 9323ba8..bf00bdb 100644
--- a/tests/plugins/core/rules/test_var_units.py
+++ b/tests/plugins/core/rules/test_var_units.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from xrlint.plugins.core.rules.var_units import VarUnits
diff --git a/tests/plugins/core/test_plugin.py b/tests/plugins/core/test_plugin.py
index c567b04..a8a6097 100644
--- a/tests/plugins/core/test_plugin.py
+++ b/tests/plugins/core/test_plugin.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.plugins.core import export_plugin
diff --git a/tests/plugins/xcube/__init__.py b/tests/plugins/xcube/__init__.py
index e69de29..f0b6197 100644
--- a/tests/plugins/xcube/__init__.py
+++ b/tests/plugins/xcube/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/plugins/xcube/helpers.py b/tests/plugins/xcube/helpers.py
index 181f0e2..a817058 100644
--- a/tests/plugins/xcube/helpers.py
+++ b/tests/plugins/xcube/helpers.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import math
 
 import numpy as np
diff --git a/tests/plugins/xcube/processors/__init__.py b/tests/plugins/xcube/processors/__init__.py
index e69de29..f0b6197 100644
--- a/tests/plugins/xcube/processors/__init__.py
+++ b/tests/plugins/xcube/processors/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/plugins/xcube/processors/test_mldataset.py b/tests/plugins/xcube/processors/test_mldataset.py
index 6ad0bcf..833de6e 100644
--- a/tests/plugins/xcube/processors/test_mldataset.py
+++ b/tests/plugins/xcube/processors/test_mldataset.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import json
 from typing import Any
 from unittest import TestCase
diff --git a/tests/plugins/xcube/rules/__init__.py b/tests/plugins/xcube/rules/__init__.py
index e69de29..f0b6197 100644
--- a/tests/plugins/xcube/rules/__init__.py
+++ b/tests/plugins/xcube/rules/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/plugins/xcube/rules/test_any_spatial_data_var.py b/tests/plugins/xcube/rules/test_any_spatial_data_var.py
index f5e847e..9b79b82 100644
--- a/tests/plugins/xcube/rules/test_any_spatial_data_var.py
+++ b/tests/plugins/xcube/rules/test_any_spatial_data_var.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.plugins.xcube.rules.any_spatial_data_var import AnySpatialDataVar
 from xrlint.testing import RuleTest, RuleTester
 
diff --git a/tests/plugins/xcube/rules/test_cube_dims_order.py b/tests/plugins/xcube/rules/test_cube_dims_order.py
index b0d1da8..c3b466a 100644
--- a/tests/plugins/xcube/rules/test_cube_dims_order.py
+++ b/tests/plugins/xcube/rules/test_cube_dims_order.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/rules/test_data_var_colors.py b/tests/plugins/xcube/rules/test_data_var_colors.py
index 4c86cf9..8c84551 100644
--- a/tests/plugins/xcube/rules/test_data_var_colors.py
+++ b/tests/plugins/xcube/rules/test_data_var_colors.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/rules/test_grid_mapping_naming.py b/tests/plugins/xcube/rules/test_grid_mapping_naming.py
index c6ca4bd..39ca479 100644
--- a/tests/plugins/xcube/rules/test_grid_mapping_naming.py
+++ b/tests/plugins/xcube/rules/test_grid_mapping_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/rules/test_increasing_time.py b/tests/plugins/xcube/rules/test_increasing_time.py
index 820f23b..4965af7 100644
--- a/tests/plugins/xcube/rules/test_increasing_time.py
+++ b/tests/plugins/xcube/rules/test_increasing_time.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/rules/test_lat_lon_naming.py b/tests/plugins/xcube/rules/test_lat_lon_naming.py
index 73f958c..e37b6c2 100644
--- a/tests/plugins/xcube/rules/test_lat_lon_naming.py
+++ b/tests/plugins/xcube/rules/test_lat_lon_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/rules/test_ml_dataset_meta.py b/tests/plugins/xcube/rules/test_ml_dataset_meta.py
index f7dd89f..31ea42a 100644
--- a/tests/plugins/xcube/rules/test_ml_dataset_meta.py
+++ b/tests/plugins/xcube/rules/test_ml_dataset_meta.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from tests.plugins.xcube.helpers import make_cube_levels
diff --git a/tests/plugins/xcube/rules/test_ml_dataset_time.py b/tests/plugins/xcube/rules/test_ml_dataset_time.py
index e0638d0..093933b 100644
--- a/tests/plugins/xcube/rules/test_ml_dataset_time.py
+++ b/tests/plugins/xcube/rules/test_ml_dataset_time.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from tests.plugins.xcube.helpers import make_cube_levels
diff --git a/tests/plugins/xcube/rules/test_ml_dataset_xy.py b/tests/plugins/xcube/rules/test_ml_dataset_xy.py
index f30860c..63f0076 100644
--- a/tests/plugins/xcube/rules/test_ml_dataset_xy.py
+++ b/tests/plugins/xcube/rules/test_ml_dataset_xy.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from tests.plugins.xcube.helpers import make_cube_levels
diff --git a/tests/plugins/xcube/rules/test_no_chunked_coords.py b/tests/plugins/xcube/rules/test_no_chunked_coords.py
index f095db2..eca9124 100644
--- a/tests/plugins/xcube/rules/test_no_chunked_coords.py
+++ b/tests/plugins/xcube/rules/test_no_chunked_coords.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import xarray as xr
 
 from tests.plugins.xcube.helpers import make_cube
diff --git a/tests/plugins/xcube/rules/test_single_grid_mapping.py b/tests/plugins/xcube/rules/test_single_grid_mapping.py
index a77984e..3ed5240 100644
--- a/tests/plugins/xcube/rules/test_single_grid_mapping.py
+++ b/tests/plugins/xcube/rules/test_single_grid_mapping.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/rules/test_time_naming.py b/tests/plugins/xcube/rules/test_time_naming.py
index 063cb52..5b61840 100644
--- a/tests/plugins/xcube/rules/test_time_naming.py
+++ b/tests/plugins/xcube/rules/test_time_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 import xarray as xr
 
diff --git a/tests/plugins/xcube/test_plugin.py b/tests/plugins/xcube/test_plugin.py
index 0c33a7b..6492078 100644
--- a/tests/plugins/xcube/test_plugin.py
+++ b/tests/plugins/xcube/test_plugin.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.plugins.xcube import export_plugin
diff --git a/tests/test_all.py b/tests/test_all.py
index df637ca..1d5c197 100644
--- a/tests/test_all.py
+++ b/tests/test_all.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 
diff --git a/tests/test_config.py b/tests/test_config.py
index 10fd893..2213947 100644
--- a/tests/test_config.py
+++ b/tests/test_config.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any
 from unittest import TestCase
 
diff --git a/tests/test_constants.py b/tests/test_constants.py
index 0b7bfb4..2f421d3 100644
--- a/tests/test_constants.py
+++ b/tests/test_constants.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.constants import SEVERITY_CODE_TO_NAME, SEVERITY_ENUM, SEVERITY_ENUM_TEXT
diff --git a/tests/test_examples.py b/tests/test_examples.py
index 1dd2824..1dad255 100644
--- a/tests/test_examples.py
+++ b/tests/test_examples.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import unittest
 from unittest import TestCase
 
diff --git a/tests/test_formatter.py b/tests/test_formatter.py
index 0275c30..c18a6d6 100644
--- a/tests/test_formatter.py
+++ b/tests/test_formatter.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.formatter import Formatter, FormatterOp, FormatterRegistry
diff --git a/tests/test_formatters.py b/tests/test_formatters.py
index fc36600..b03fd7e 100644
--- a/tests/test_formatters.py
+++ b/tests/test_formatters.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.formatters import export_formatters
diff --git a/tests/test_linter.py b/tests/test_linter.py
index 27a7594..752d0f1 100644
--- a/tests/test_linter.py
+++ b/tests/test_linter.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any
 from unittest import TestCase
 
diff --git a/tests/test_node.py b/tests/test_node.py
index a1cd4e0..8f305e9 100644
--- a/tests/test_node.py
+++ b/tests/test_node.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.node import XarrayNode
diff --git a/tests/test_operation.py b/tests/test_operation.py
index 7a0e286..86ef42c 100644
--- a/tests/test_operation.py
+++ b/tests/test_operation.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from abc import ABC
 from dataclasses import dataclass
 from typing import Type
diff --git a/tests/test_plugin.py b/tests/test_plugin.py
index b9e46bd..f7b610c 100644
--- a/tests/test_plugin.py
+++ b/tests/test_plugin.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any
 from unittest import TestCase
 
diff --git a/tests/test_processor.py b/tests/test_processor.py
index 6bc7898..8d70d08 100644
--- a/tests/test_processor.py
+++ b/tests/test_processor.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any
 from unittest import TestCase
 
diff --git a/tests/test_result.py b/tests/test_result.py
index 546ef72..722f571 100644
--- a/tests/test_result.py
+++ b/tests/test_result.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.config import ConfigObject
diff --git a/tests/test_rule.py b/tests/test_rule.py
index bbdc4ac..ef03384 100644
--- a/tests/test_rule.py
+++ b/tests/test_rule.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import unittest
 from unittest import TestCase
 
diff --git a/tests/test_testing.py b/tests/test_testing.py
index 7ee728c..070748f 100644
--- a/tests/test_testing.py
+++ b/tests/test_testing.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 import pytest
diff --git a/tests/util/__init__.py b/tests/util/__init__.py
index e69de29..f0b6197 100644
--- a/tests/util/__init__.py
+++ b/tests/util/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/util/test_constructible.py b/tests/util/test_constructible.py
index daa5648..41443e9 100644
--- a/tests/util/test_constructible.py
+++ b/tests/util/test_constructible.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from dataclasses import dataclass, field
 from types import NoneType, UnionType
 from typing import (
diff --git a/tests/util/test_filefilter.py b/tests/util/test_filefilter.py
index 2811df2..6adec74 100644
--- a/tests/util/test_filefilter.py
+++ b/tests/util/test_filefilter.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import unittest
 
 from xrlint.util.filefilter import FileFilter
diff --git a/tests/util/test_filepattern.py b/tests/util/test_filepattern.py
index fdddc1d..800ece7 100644
--- a/tests/util/test_filepattern.py
+++ b/tests/util/test_filepattern.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import unittest
 
 from xrlint.util.filepattern import FilePattern
diff --git a/tests/util/test_formatting.py b/tests/util/test_formatting.py
index 44d6fcb..20368ef 100644
--- a/tests/util/test_formatting.py
+++ b/tests/util/test_formatting.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.util.formatting import (
diff --git a/tests/util/test_importutil.py b/tests/util/test_importutil.py
index f194832..ecee2b5 100644
--- a/tests/util/test_importutil.py
+++ b/tests/util/test_importutil.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 import pytest
diff --git a/tests/util/test_importutil_pkg/__init__.py b/tests/util/test_importutil_pkg/__init__.py
index e69de29..f0b6197 100644
--- a/tests/util/test_importutil_pkg/__init__.py
+++ b/tests/util/test_importutil_pkg/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/util/test_importutil_pkg/module1.py b/tests/util/test_importutil_pkg/module1.py
index e69de29..f0b6197 100644
--- a/tests/util/test_importutil_pkg/module1.py
+++ b/tests/util/test_importutil_pkg/module1.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/util/test_importutil_pkg/module2/__init__.py b/tests/util/test_importutil_pkg/module2/__init__.py
index e69de29..f0b6197 100644
--- a/tests/util/test_importutil_pkg/module2/__init__.py
+++ b/tests/util/test_importutil_pkg/module2/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/tests/util/test_merge.py b/tests/util/test_merge.py
index 53ca8cc..f86628e 100644
--- a/tests/util/test_merge.py
+++ b/tests/util/test_merge.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.util.merge import merge_arrays, merge_dicts, merge_set_lists, merge_values
diff --git a/tests/util/test_naming.py b/tests/util/test_naming.py
index cfcd6b3..6801dc9 100644
--- a/tests/util/test_naming.py
+++ b/tests/util/test_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 from xrlint.util.naming import to_kebab_case, to_snake_case
diff --git a/tests/util/test_schema.py b/tests/util/test_schema.py
index 7dda65e..490ae3f 100644
--- a/tests/util/test_schema.py
+++ b/tests/util/test_schema.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from unittest import TestCase
 
 import pytest
diff --git a/tests/util/test_serializable.py b/tests/util/test_serializable.py
index af100bf..ec950b4 100644
--- a/tests/util/test_serializable.py
+++ b/tests/util/test_serializable.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from dataclasses import dataclass, field
 from typing import Any, Literal
 from unittest import TestCase
diff --git a/xrlint/__init__.py b/xrlint/__init__.py
index 5af3b6e..59ab44a 100644
--- a/xrlint/__init__.py
+++ b/xrlint/__init__.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 # No other imports here!
 from .version import version
 
diff --git a/xrlint/_linter/__init__.py b/xrlint/_linter/__init__.py
index 84d38c2..c552501 100644
--- a/xrlint/_linter/__init__.py
+++ b/xrlint/_linter/__init__.py
@@ -1 +1,5 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 # Empty by intention.
diff --git a/xrlint/_linter/apply.py b/xrlint/_linter/apply.py
index 5e427e1..ade4959 100644
--- a/xrlint/_linter/apply.py
+++ b/xrlint/_linter/apply.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import AttrNode, AttrsNode, DatasetNode, VariableNode
 from xrlint.rule import RuleConfig, RuleExit, RuleOp
 
diff --git a/xrlint/_linter/rulectx.py b/xrlint/_linter/rulectx.py
index 1abfec6..1a1df73 100644
--- a/xrlint/_linter/rulectx.py
+++ b/xrlint/_linter/rulectx.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import contextlib
 from typing import Any, Literal
 
diff --git a/xrlint/_linter/validate.py b/xrlint/_linter/validate.py
index 4217b40..8c962ac 100644
--- a/xrlint/_linter/validate.py
+++ b/xrlint/_linter/validate.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import time
 from typing import Any
 
diff --git a/xrlint/all.py b/xrlint/all.py
index c8bdba9..4009c16 100644
--- a/xrlint/all.py
+++ b/xrlint/all.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.cli.engine import XRLint
 from xrlint.config import Config, ConfigLike, ConfigObject, ConfigObjectLike
 from xrlint.formatter import (
diff --git a/xrlint/cli/__init__.py b/xrlint/cli/__init__.py
index 84d38c2..c552501 100644
--- a/xrlint/cli/__init__.py
+++ b/xrlint/cli/__init__.py
@@ -1 +1,5 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 # Empty by intention.
diff --git a/xrlint/cli/config.py b/xrlint/cli/config.py
index 9e4ef41..1a9342c 100644
--- a/xrlint/cli/config.py
+++ b/xrlint/cli/config.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import sys
 from os import PathLike
 from pathlib import Path
diff --git a/xrlint/cli/constants.py b/xrlint/cli/constants.py
index f5d29bd..a8fad7d 100644
--- a/xrlint/cli/constants.py
+++ b/xrlint/cli/constants.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Final
 
 DEFAULT_CONFIG_BASENAME: Final = "xrlint_config"
diff --git a/xrlint/cli/engine.py b/xrlint/cli/engine.py
index 703a58f..43c6b36 100644
--- a/xrlint/cli/engine.py
+++ b/xrlint/cli/engine.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import json
 import os
 from collections.abc import Iterable, Iterator
diff --git a/xrlint/cli/main.py b/xrlint/cli/main.py
index 702d22a..efac007 100644
--- a/xrlint/cli/main.py
+++ b/xrlint/cli/main.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import sys
 
 import click
diff --git a/xrlint/config.py b/xrlint/config.py
index 572a15f..014fd7c 100644
--- a/xrlint/config.py
+++ b/xrlint/config.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import Mapping, Sequence
 from dataclasses import dataclass, field
 from functools import cached_property
diff --git a/xrlint/constants.py b/xrlint/constants.py
index a12cee5..5eff952 100644
--- a/xrlint/constants.py
+++ b/xrlint/constants.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Final
 
 CORE_PLUGIN_NAME: Final = "__core__"
diff --git a/xrlint/formatter.py b/xrlint/formatter.py
index 5293388..1519bd3 100644
--- a/xrlint/formatter.py
+++ b/xrlint/formatter.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from abc import ABC, abstractmethod
 from collections.abc import Iterable, Mapping
 from dataclasses import dataclass
diff --git a/xrlint/formatters/__init__.py b/xrlint/formatters/__init__.py
index fe43daa..a88a8ee 100644
--- a/xrlint/formatters/__init__.py
+++ b/xrlint/formatters/__init__.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.formatter import FormatterRegistry
 from xrlint.util.importutil import import_submodules
 
diff --git a/xrlint/formatters/html.py b/xrlint/formatters/html.py
index 0a20600..bec1788 100644
--- a/xrlint/formatters/html.py
+++ b/xrlint/formatters/html.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import html
 from collections.abc import Iterable
 
diff --git a/xrlint/formatters/json.py b/xrlint/formatters/json.py
index ecdfc4c..ce10a66 100644
--- a/xrlint/formatters/json.py
+++ b/xrlint/formatters/json.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import json
 from collections.abc import Iterable
 
diff --git a/xrlint/formatters/simple.py b/xrlint/formatters/simple.py
index b273b77..5661d44 100644
--- a/xrlint/formatters/simple.py
+++ b/xrlint/formatters/simple.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import Iterable
 
 from tabulate import tabulate
diff --git a/xrlint/linter.py b/xrlint/linter.py
index b265e31..e6e8d3c 100644
--- a/xrlint/linter.py
+++ b/xrlint/linter.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from os import PathLike
 from pathlib import Path
 from typing import Any
diff --git a/xrlint/node.py b/xrlint/node.py
index 4c78bdf..95ef739 100644
--- a/xrlint/node.py
+++ b/xrlint/node.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from abc import ABC
 from dataclasses import dataclass
 from typing import Any, Hashable, Union
diff --git a/xrlint/operation.py b/xrlint/operation.py
index 79a1005..b87c004 100644
--- a/xrlint/operation.py
+++ b/xrlint/operation.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import MutableMapping
 from dataclasses import dataclass
 from inspect import getdoc, isclass
diff --git a/xrlint/plugin.py b/xrlint/plugin.py
index 38ec781..d5b6d11 100644
--- a/xrlint/plugin.py
+++ b/xrlint/plugin.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from dataclasses import dataclass, field
 from typing import Any, Callable, Literal, Type
 
diff --git a/xrlint/plugins/__init__.py b/xrlint/plugins/__init__.py
index 84d38c2..c552501 100644
--- a/xrlint/plugins/__init__.py
+++ b/xrlint/plugins/__init__.py
@@ -1 +1,5 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 # Empty by intention.
diff --git a/xrlint/plugins/core/__init__.py b/xrlint/plugins/core/__init__.py
index eed907e..cb0ce3e 100644
--- a/xrlint/plugins/core/__init__.py
+++ b/xrlint/plugins/core/__init__.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.plugin import Plugin
 from xrlint.util.importutil import import_submodules
 
diff --git a/xrlint/plugins/core/plugin.py b/xrlint/plugins/core/plugin.py
index 2332830..d6e142d 100644
--- a/xrlint/plugins/core/plugin.py
+++ b/xrlint/plugins/core/plugin.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.constants import CORE_DOCS_URL, CORE_PLUGIN_NAME
 from xrlint.plugin import new_plugin
 from xrlint.version import version
diff --git a/xrlint/plugins/core/rules/__init__.py b/xrlint/plugins/core/rules/__init__.py
index e69de29..f0b6197 100644
--- a/xrlint/plugins/core/rules/__init__.py
+++ b/xrlint/plugins/core/rules/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/xrlint/plugins/core/rules/content_desc.py b/xrlint/plugins/core/rules/content_desc.py
index b0664b2..3d4152e 100644
--- a/xrlint/plugins/core/rules/content_desc.py
+++ b/xrlint/plugins/core/rules/content_desc.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import re
 
 from xrlint.node import DatasetNode, VariableNode
diff --git a/xrlint/plugins/core/rules/conventions.py b/xrlint/plugins/core/rules/conventions.py
index dcb4ce3..f116047 100644
--- a/xrlint/plugins/core/rules/conventions.py
+++ b/xrlint/plugins/core/rules/conventions.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import re
 
 from xrlint.node import DatasetNode
diff --git a/xrlint/plugins/core/rules/coords_for_dims.py b/xrlint/plugins/core/rules/coords_for_dims.py
index be0d261..30d0e23 100644
--- a/xrlint/plugins/core/rules/coords_for_dims.py
+++ b/xrlint/plugins/core/rules/coords_for_dims.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.core.plugin import plugin
 from xrlint.rule import RuleContext, RuleOp
diff --git a/xrlint/plugins/core/rules/grid_mappings.py b/xrlint/plugins/core/rules/grid_mappings.py
index 170b446..dfdc355 100644
--- a/xrlint/plugins/core/rules/grid_mappings.py
+++ b/xrlint/plugins/core/rules/grid_mappings.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.core.plugin import plugin
 from xrlint.rule import RuleContext, RuleOp
diff --git a/xrlint/plugins/core/rules/lat_lon_coordinate.py b/xrlint/plugins/core/rules/lat_lon_coordinate.py
index 256bb9d..0a85741 100644
--- a/xrlint/plugins/core/rules/lat_lon_coordinate.py
+++ b/xrlint/plugins/core/rules/lat_lon_coordinate.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any
 
 import xarray as xr
diff --git a/xrlint/plugins/core/rules/no_empty_attrs.py b/xrlint/plugins/core/rules/no_empty_attrs.py
index 2ea0613..21d1057 100644
--- a/xrlint/plugins/core/rules/no_empty_attrs.py
+++ b/xrlint/plugins/core/rules/no_empty_attrs.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import AttrsNode
 from xrlint.plugins.core.plugin import plugin
 from xrlint.result import Suggestion
diff --git a/xrlint/plugins/core/rules/no_empty_chunks.py b/xrlint/plugins/core/rules/no_empty_chunks.py
index 6a0833a..8fdfa37 100644
--- a/xrlint/plugins/core/rules/no_empty_chunks.py
+++ b/xrlint/plugins/core/rules/no_empty_chunks.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.core.plugin import plugin
 from xrlint.rule import RuleContext, RuleExit, RuleOp
diff --git a/xrlint/plugins/core/rules/time_coordinate.py b/xrlint/plugins/core/rules/time_coordinate.py
index e48ab6b..1fc39f6 100644
--- a/xrlint/plugins/core/rules/time_coordinate.py
+++ b/xrlint/plugins/core/rules/time_coordinate.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import re
 
 from xrlint.node import VariableNode
diff --git a/xrlint/plugins/core/rules/var_desc.py b/xrlint/plugins/core/rules/var_desc.py
index 3bde393..d4200f8 100644
--- a/xrlint/plugins/core/rules/var_desc.py
+++ b/xrlint/plugins/core/rules/var_desc.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import VariableNode
 from xrlint.plugins.core.plugin import plugin
 from xrlint.rule import RuleContext, RuleOp
diff --git a/xrlint/plugins/core/rules/var_flags.py b/xrlint/plugins/core/rules/var_flags.py
index b198964..c3510ed 100644
--- a/xrlint/plugins/core/rules/var_flags.py
+++ b/xrlint/plugins/core/rules/var_flags.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any
 
 import numpy as np
diff --git a/xrlint/plugins/core/rules/var_units.py b/xrlint/plugins/core/rules/var_units.py
index 599b627..99374c6 100644
--- a/xrlint/plugins/core/rules/var_units.py
+++ b/xrlint/plugins/core/rules/var_units.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import VariableNode
 from xrlint.plugins.core.plugin import plugin
 from xrlint.rule import RuleContext, RuleOp
diff --git a/xrlint/plugins/xcube/__init__.py b/xrlint/plugins/xcube/__init__.py
index 899e544..31ed245 100644
--- a/xrlint/plugins/xcube/__init__.py
+++ b/xrlint/plugins/xcube/__init__.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.plugin import Plugin
 from xrlint.plugins.xcube.constants import ML_FILE_PATTERN
 from xrlint.util.importutil import import_submodules
diff --git a/xrlint/plugins/xcube/constants.py b/xrlint/plugins/xcube/constants.py
index b10b532..8169e20 100644
--- a/xrlint/plugins/xcube/constants.py
+++ b/xrlint/plugins/xcube/constants.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Final
 
 LON_NAME: Final = "lon"
diff --git a/xrlint/plugins/xcube/plugin.py b/xrlint/plugins/xcube/plugin.py
index ae40b4a..0816b8d 100644
--- a/xrlint/plugins/xcube/plugin.py
+++ b/xrlint/plugins/xcube/plugin.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.plugin import new_plugin
 from xrlint.version import version
 
diff --git a/xrlint/plugins/xcube/processors/__init__.py b/xrlint/plugins/xcube/processors/__init__.py
index e69de29..f0b6197 100644
--- a/xrlint/plugins/xcube/processors/__init__.py
+++ b/xrlint/plugins/xcube/processors/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/xrlint/plugins/xcube/processors/mldataset.py b/xrlint/plugins/xcube/processors/mldataset.py
index 0d5a49b..e909766 100644
--- a/xrlint/plugins/xcube/processors/mldataset.py
+++ b/xrlint/plugins/xcube/processors/mldataset.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import itertools
 import json
 import re
diff --git a/xrlint/plugins/xcube/rules/__init__.py b/xrlint/plugins/xcube/rules/__init__.py
index e69de29..f0b6197 100644
--- a/xrlint/plugins/xcube/rules/__init__.py
+++ b/xrlint/plugins/xcube/rules/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/xrlint/plugins/xcube/rules/any_spatial_data_var.py b/xrlint/plugins/xcube/rules/any_spatial_data_var.py
index 030b873..c4dd296 100644
--- a/xrlint/plugins/xcube/rules/any_spatial_data_var.py
+++ b/xrlint/plugins/xcube/rules/any_spatial_data_var.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.plugin import plugin
 from xrlint.plugins.xcube.util import is_spatial_var
diff --git a/xrlint/plugins/xcube/rules/cube_dims_order.py b/xrlint/plugins/xcube/rules/cube_dims_order.py
index dc87e50..66da4d3 100644
--- a/xrlint/plugins/xcube/rules/cube_dims_order.py
+++ b/xrlint/plugins/xcube/rules/cube_dims_order.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import VariableNode
 from xrlint.plugins.xcube.constants import LAT_NAME, LON_NAME, TIME_NAME, X_NAME, Y_NAME
 from xrlint.plugins.xcube.plugin import plugin
diff --git a/xrlint/plugins/xcube/rules/data_var_colors.py b/xrlint/plugins/xcube/rules/data_var_colors.py
index 2435fd5..fa43112 100644
--- a/xrlint/plugins/xcube/rules/data_var_colors.py
+++ b/xrlint/plugins/xcube/rules/data_var_colors.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import VariableNode
 from xrlint.plugins.xcube.plugin import plugin
 from xrlint.plugins.xcube.util import is_spatial_var
diff --git a/xrlint/plugins/xcube/rules/dataset_title.py b/xrlint/plugins/xcube/rules/dataset_title.py
index 4fad707..0af5c23 100644
--- a/xrlint/plugins/xcube/rules/dataset_title.py
+++ b/xrlint/plugins/xcube/rules/dataset_title.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.plugin import plugin
 from xrlint.rule import RuleContext, RuleOp
diff --git a/xrlint/plugins/xcube/rules/grid_mapping_naming.py b/xrlint/plugins/xcube/rules/grid_mapping_naming.py
index 953439e..53b6585 100644
--- a/xrlint/plugins/xcube/rules/grid_mapping_naming.py
+++ b/xrlint/plugins/xcube/rules/grid_mapping_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.constants import GM_NAMES, GM_NAMES_TEXT
 from xrlint.plugins.xcube.plugin import plugin
diff --git a/xrlint/plugins/xcube/rules/increasing_time.py b/xrlint/plugins/xcube/rules/increasing_time.py
index e48073c..8a3a239 100644
--- a/xrlint/plugins/xcube/rules/increasing_time.py
+++ b/xrlint/plugins/xcube/rules/increasing_time.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import numpy as np
 
 from xrlint.node import VariableNode
diff --git a/xrlint/plugins/xcube/rules/lat_lon_naming.py b/xrlint/plugins/xcube/rules/lat_lon_naming.py
index 8f71a8f..1f8ff7d 100644
--- a/xrlint/plugins/xcube/rules/lat_lon_naming.py
+++ b/xrlint/plugins/xcube/rules/lat_lon_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.constants import LAT_NAME, LON_NAME
 from xrlint.plugins.xcube.plugin import plugin
diff --git a/xrlint/plugins/xcube/rules/ml_dataset_meta.py b/xrlint/plugins/xcube/rules/ml_dataset_meta.py
index a1e53a0..3e51b0f 100644
--- a/xrlint/plugins/xcube/rules/ml_dataset_meta.py
+++ b/xrlint/plugins/xcube/rules/ml_dataset_meta.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.constants import ML_META_FILENAME
 from xrlint.plugins.xcube.plugin import plugin
diff --git a/xrlint/plugins/xcube/rules/ml_dataset_time.py b/xrlint/plugins/xcube/rules/ml_dataset_time.py
index 5f48a3e..80487e8 100644
--- a/xrlint/plugins/xcube/rules/ml_dataset_time.py
+++ b/xrlint/plugins/xcube/rules/ml_dataset_time.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.constants import TIME_NAME
 from xrlint.plugins.xcube.plugin import plugin
diff --git a/xrlint/plugins/xcube/rules/ml_dataset_xy.py b/xrlint/plugins/xcube/rules/ml_dataset_xy.py
index fd1540d..822b4cd 100644
--- a/xrlint/plugins/xcube/rules/ml_dataset_xy.py
+++ b/xrlint/plugins/xcube/rules/ml_dataset_xy.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import math
 
 from xrlint.node import DatasetNode
diff --git a/xrlint/plugins/xcube/rules/no_chunked_coords.py b/xrlint/plugins/xcube/rules/no_chunked_coords.py
index 9f577f0..8b68135 100644
--- a/xrlint/plugins/xcube/rules/no_chunked_coords.py
+++ b/xrlint/plugins/xcube/rules/no_chunked_coords.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import math
 
 from xrlint.node import VariableNode
diff --git a/xrlint/plugins/xcube/rules/single_grid_mapping.py b/xrlint/plugins/xcube/rules/single_grid_mapping.py
index e788f9b..42c79c3 100644
--- a/xrlint/plugins/xcube/rules/single_grid_mapping.py
+++ b/xrlint/plugins/xcube/rules/single_grid_mapping.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from xrlint.node import DatasetNode
 from xrlint.plugins.xcube.constants import GM_NAMES_TEXT, LAT_NAME, LON_NAME
 from xrlint.plugins.xcube.plugin import plugin
diff --git a/xrlint/plugins/xcube/rules/time_naming.py b/xrlint/plugins/xcube/rules/time_naming.py
index 1f69db3..e9f6a4b 100644
--- a/xrlint/plugins/xcube/rules/time_naming.py
+++ b/xrlint/plugins/xcube/rules/time_naming.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import Hashable
 from typing import Any
 
diff --git a/xrlint/plugins/xcube/util.py b/xrlint/plugins/xcube/util.py
index 22726f0..0a7e6b7 100644
--- a/xrlint/plugins/xcube/util.py
+++ b/xrlint/plugins/xcube/util.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import Hashable
 from dataclasses import dataclass
 
diff --git a/xrlint/processor.py b/xrlint/processor.py
index f763c00..94dbb2c 100644
--- a/xrlint/processor.py
+++ b/xrlint/processor.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from abc import ABC, abstractmethod
 from dataclasses import dataclass
 from typing import Any, Callable, Type
diff --git a/xrlint/result.py b/xrlint/result.py
index df9abe9..b1fac09 100644
--- a/xrlint/result.py
+++ b/xrlint/result.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import Iterable
 from dataclasses import dataclass, field
 from typing import TYPE_CHECKING, Literal, Union
diff --git a/xrlint/rule.py b/xrlint/rule.py
index 5ea209d..9906180 100644
--- a/xrlint/rule.py
+++ b/xrlint/rule.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from abc import ABC, abstractmethod
 from collections.abc import MutableMapping, Sequence
 from dataclasses import dataclass, field
diff --git a/xrlint/testing.py b/xrlint/testing.py
index 35445d4..96dd1e0 100644
--- a/xrlint/testing.py
+++ b/xrlint/testing.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import unittest
 from dataclasses import dataclass
 from typing import Any, Callable, Final, Literal, Type
diff --git a/xrlint/util/__init__.py b/xrlint/util/__init__.py
index e69de29..f0b6197 100644
--- a/xrlint/util/__init__.py
+++ b/xrlint/util/__init__.py
@@ -0,0 +1,4 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
diff --git a/xrlint/util/constructible.py b/xrlint/util/constructible.py
index 37e33d9..e0a7f62 100644
--- a/xrlint/util/constructible.py
+++ b/xrlint/util/constructible.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import sys
 from collections.abc import Mapping, Sequence
 from functools import lru_cache
diff --git a/xrlint/util/filefilter.py b/xrlint/util/filefilter.py
index e295b67..32a7502 100644
--- a/xrlint/util/filefilter.py
+++ b/xrlint/util/filefilter.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from dataclasses import dataclass
 
 from xrlint.util.filepattern import FilePattern
diff --git a/xrlint/util/filepattern.py b/xrlint/util/filepattern.py
index b90836c..ebdd39d 100644
--- a/xrlint/util/filepattern.py
+++ b/xrlint/util/filepattern.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import platform
 import re
 from functools import cached_property
diff --git a/xrlint/util/formatting.py b/xrlint/util/formatting.py
index 30b9e9a..87853aa 100644
--- a/xrlint/util/formatting.py
+++ b/xrlint/util/formatting.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from collections.abc import Sequence
 from typing import Any
 
diff --git a/xrlint/util/importutil.py b/xrlint/util/importutil.py
index fbb35d5..6506091 100644
--- a/xrlint/util/importutil.py
+++ b/xrlint/util/importutil.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 import importlib
 import pathlib
 from typing import Any, Callable, Type, TypeVar
diff --git a/xrlint/util/merge.py b/xrlint/util/merge.py
index e1f77a5..403e59f 100644
--- a/xrlint/util/merge.py
+++ b/xrlint/util/merge.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any, Callable
 
 
diff --git a/xrlint/util/naming.py b/xrlint/util/naming.py
index 40f29ba..0ee764e 100644
--- a/xrlint/util/naming.py
+++ b/xrlint/util/naming.py
@@ -1,3 +1,8 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
+
 def to_kebab_case(name: str) -> str:
     return _to_lc_case(name, "-")
 
diff --git a/xrlint/util/schema.py b/xrlint/util/schema.py
index b2b1e6d..bf8c5c7 100644
--- a/xrlint/util/schema.py
+++ b/xrlint/util/schema.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from typing import Any, Literal
 
 from .formatting import format_message_one_of, format_message_type_of
diff --git a/xrlint/util/serializable.py b/xrlint/util/serializable.py
index 580f681..4f9a4b9 100644
--- a/xrlint/util/serializable.py
+++ b/xrlint/util/serializable.py
@@ -1,3 +1,7 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 from dataclasses import fields, is_dataclass
 from typing import Any, Final, Mapping, Sequence, TypeAlias
 
diff --git a/xrlint/version.py b/xrlint/version.py
index fbf508b..8fecd05 100644
--- a/xrlint/version.py
+++ b/xrlint/version.py
@@ -1 +1,5 @@
+#  Copyright © 2025 Brockmann Consult GmbH.
+#  This software is distributed under the terms and conditions of the
+#  MIT license (https://mit-license.org/).
+
 version = "0.5.0.dev0"