diff --git a/Makefile b/Makefile
index 95d5ca1..b764be7 100644
--- a/Makefile
+++ b/Makefile
@@ -1,21 +1,20 @@
 src := mltb2
-test-src := tests
-other-src := setup.py docs
+other-src := tests docs
 
 check:
-	poetry run black $(src) $(test-src) --check --diff
-	poetry run mypy --install-types --non-interactive $(src) $(test-src)
-	poetry run ruff $(src) $(test-src)
+	poetry run black $(src) $(other-src) --check --diff
+	poetry run mypy --install-types --non-interactive $(src) $(other-src)
+	poetry run ruff $(src) $(other-src)
 	poetry run mdformat --check --number .
 	poetry run make -C docs clean doctest
 
 format:
-	poetry run black $(src) $(test-src)
-	poetry run ruff $(src) $(test-src) --fix
+	poetry run black $(src) $(other-src)
+	poetry run ruff $(src) $(other-src) --fix
 	poetry run mdformat --number .
 
 test:
-	poetry run pytest $(test-src)
+	poetry run pytest $(other-src)
 
 sphinx:
 	poetry run make -C docs clean html
diff --git a/docs/source/conf.py b/docs/source/conf.py
index 85e4d41..35a7530 100644
--- a/docs/source/conf.py
+++ b/docs/source/conf.py
@@ -1,3 +1,7 @@
+# Copyright (c) 2023 Philip May
+# This software is distributed under the terms of the MIT license
+# which is available at https://opensource.org/licenses/MIT
+
 """Configuration for the Sphinx documentation builder."""
 
 # Configuration file for the Sphinx documentation builder.
@@ -17,11 +21,10 @@
 # sys.path.insert(0, os.path.abspath('.'))
 from typing import List
 
-
 # -- Project information -----------------------------------------------------
 
 project = "MLTB2"
-copyright = "2023, Philip May, Deutsche Telekom AG"
+copyright = "2023, Philip May, Deutsche Telekom AG"  # noqa: A001
 author = "Philip May"
 
 
@@ -70,9 +73,11 @@
     # "transformers": ("https://huggingface.co/transformers/", None),
     "optuna": ("https://optuna.readthedocs.io/en/stable/", None),
     "mlflow": ("https://www.mlflow.org/docs/latest/", None),
-    "scipy": ("https://docs.scipy.org/doc/scipy/reference/", None),
+    "scipy": ("https://docs.scipy.org/doc/scipy/", None),
     "numpy": ("https://numpy.org/doc/stable/", None),
     "git": ("https://gitpython.readthedocs.io/en/stable/", None),
+    "platformdirs": ("https://platformdirs.readthedocs.io/en/latest/", None),
+    # "matplotlib": ("https://matplotlib.org/stable/", None),
 }
 
 # html_logo = "imgs/xxx.png"
diff --git a/mltb2/data.py b/mltb2/data.py
index de7a277..3613d38 100644
--- a/mltb2/data.py
+++ b/mltb2/data.py
@@ -4,10 +4,21 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""Data loading module.
+"""This module offers tools for loading data.
 
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[data]``
+The following tabular data sets from the biological and medical domain are supported:
+
+- colon: `<http://genomics-pubs.princeton.edu/oncology/affydata/index.html>`_
+- prostate: `<https://web.stanford.edu/~hastie/CASI_files/DATA/prostate.html>`_
+- leukemia_big: `<https://web.stanford.edu/~hastie/CASI_files/DATA/leukemia.html>`_
+
+After loading the data from the internet it is parsed, converted and
+cached in the mltb2 data directory.
+This data directory is determined by :func:`mltb2.files.get_and_create_mltb2_data_dir`.
+
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[data]``
 """
 
 import os
diff --git a/mltb2/fasttext.py b/mltb2/fasttext.py
index 851ad8b..8d2dda7 100644
--- a/mltb2/fasttext.py
+++ b/mltb2/fasttext.py
@@ -2,11 +2,11 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""fastText specific module.
+"""This module offers tools for `fastText <https://fasttext.cc/docs/en/support.html>`_.
 
-This module is based on `fastText <https://fasttext.cc/docs/en/support.html>`_.
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[fasttext]``
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[fasttext]``
 """
 
 import os
diff --git a/mltb2/files.py b/mltb2/files.py
index 468fbac..1eb0e57 100644
--- a/mltb2/files.py
+++ b/mltb2/files.py
@@ -4,8 +4,11 @@
 
 """File utils module.
 
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[files]``
+This module provides utility functions for other modules.
+
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[files]``
 """
 
 
@@ -18,11 +21,15 @@
 
 
 def get_and_create_mltb2_data_dir(mltb2_base_data_dir: Optional[str] = None) -> str:
-    """Return and create mltb data dir.
+    """Return and create a data dir for mltb2.
+
+    The exact directory is given by the ``mltb2_base_data_dir`` as the base folder
+    and then the folder ``mltb2`` is appended.
 
     Args:
         mltb2_base_data_dir: The base data directory. If ``None`` the default
-            user data directory is used.
+            user data directory is used. The default user data directory is
+            determined by :func:`platformdirs.user_data_dir`.
 
     Returns:
         The directory path.
diff --git a/mltb2/md.py b/mltb2/md.py
index 5d21e5b..62f2c6d 100644
--- a/mltb2/md.py
+++ b/mltb2/md.py
@@ -5,8 +5,9 @@
 
 """Markdown specific module.
 
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[md]``
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[md]``
 """
 
 import re
diff --git a/mltb2/openai.py b/mltb2/openai.py
index bdc3eb3..749f332 100644
--- a/mltb2/openai.py
+++ b/mltb2/openai.py
@@ -4,8 +4,9 @@
 
 """OpenAI specific module.
 
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[openai]``
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[openai]``
 """
 
 
diff --git a/mltb2/optuna.py b/mltb2/optuna.py
index 75689c3..ec8e830 100644
--- a/mltb2/optuna.py
+++ b/mltb2/optuna.py
@@ -2,11 +2,11 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""Optuna specific module.
+"""This module offers tools for `Optuna <https://optuna.readthedocs.io/en/stable/>`_.
 
-This module is based on `Optuna <https://optuna.readthedocs.io/en/stable/>`_.
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[optuna]``
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[optuna]``
 """
 
 
diff --git a/mltb2/plot.py b/mltb2/plot.py
index 875ace8..db7cf46 100644
--- a/mltb2/plot.py
+++ b/mltb2/plot.py
@@ -5,8 +5,10 @@
 """Plot tools module.
 
 This module is based on `Matplotlib <https://matplotlib.org/>`_.
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[plot]``
+
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[plot]``
 """
 
 from typing import Optional
@@ -31,7 +33,9 @@ def twin_axes_timeseries_plot(
     """Create twin axes timeseries plot.
 
     Plots two different timeseries curves in one diagram but two different y-axes.
-    This function does not call `matplotlib.pyplot.plot()`.
+
+    Hint:
+        This function does not use `matplotlib.pyplot.plot`.
 
     Args:
         values_1: (``array_like``) Values for the first timeseries curve.
@@ -88,7 +92,8 @@ def boxplot(
 ):
     """Prints one or more boxplots in a single diagram.
 
-    This function does not call `matplotlib.pyplot.plot()`.
+    Hint:
+        This function does not use `matplotlib.pyplot.plot`.
 
     Args:
         values: Values for the boxplot(s).
@@ -131,7 +136,8 @@ def boxplot_dict(
 ):
     """Create boxplot form dictionary.
 
-    This function does not call `matplotlib.pyplot.plot()`.
+    Hint:
+        This function does not use `matplotlib.pyplot.plot`.
 
     Args:
         values_dict: Dictionary with values for the boxplot(s).
@@ -152,7 +158,7 @@ def boxplot_dict(
 
 
 def save_last_figure(filename):
-    """Saves the last plot.
+    """Saves the last plot made by Matplotlib.
 
     For jupyter notebooks this has to be called in the same cell that created the plot.
     """
diff --git a/mltb2/somajo.py b/mltb2/somajo.py
index 5b97c3a..29556fb 100644
--- a/mltb2/somajo.py
+++ b/mltb2/somajo.py
@@ -2,11 +2,11 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""SoMaJo specific module.
+"""This module offers `SoMaJo <https://github.com/tsproisl/SoMaJo>`_ specific tools.
 
-This module is based on `SoMaJo <https://github.com/tsproisl/SoMaJo>`_.
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[somajo]``
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[somajo]``
 """
 
 
diff --git a/mltb2/somajo_transformers.py b/mltb2/somajo_transformers.py
index 18b76ef..82a4b3c 100644
--- a/mltb2/somajo_transformers.py
+++ b/mltb2/somajo_transformers.py
@@ -3,13 +3,15 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""Hugging Face Transformers and SoMaJo specific module.
+"""This module offers Hugging Face Transformers and SoMaJo specific tools.
 
 This module is based on
 `Hugging Face Transformers <https://huggingface.co/docs/transformers/index>`_ and
 `SoMaJo <https://github.com/tsproisl/SoMaJo>`_.
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[somajo_transformers]``
+
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[somajo_transformers]``
 """
 
 
diff --git a/mltb2/text.py b/mltb2/text.py
index 2138347..d721e87 100644
--- a/mltb2/text.py
+++ b/mltb2/text.py
@@ -2,7 +2,14 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""Text specific module."""
+"""This module offers text specific tools.
+
+It offers the following functionality:
+
+- detect or clean invisible characters
+- detect or replace special whitespaces
+- remove duplicate whitespaces
+"""
 
 import re
 from typing import Dict, Final, Pattern, Tuple
diff --git a/mltb2/transformers.py b/mltb2/transformers.py
index fcea39f..882e37f 100644
--- a/mltb2/transformers.py
+++ b/mltb2/transformers.py
@@ -2,12 +2,11 @@
 # This software is distributed under the terms of the MIT license
 # which is available at https://opensource.org/licenses/MIT
 
-"""Hugging Face Transformers specific module.
+"""This module offers `Hugging Face Transformers <https://huggingface.co/docs/transformers/index>`_ specific tools.
 
-This module is based on
-`Hugging Face Transformers <https://huggingface.co/docs/transformers/index>`_.
-Use pip to install the necessary dependencies for this module:
-``pip install mltb2[transformers]``
+Hint:
+    Use pip to install the necessary dependencies for this module:
+    ``pip install mltb2[transformers]``
 """
 
 import os