diff --git a/.gitignore b/.gitignore
index cc5fd82c..0950d03e 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,6 +14,7 @@ install
 .venv
 __pycache__
 *.pyc
+*.egg-info
 
 # IDEs / editors
 .idea
diff --git a/python-aux/README.md b/python-aux/README.md
new file mode 100644
index 00000000..7b2d780c
--- /dev/null
+++ b/python-aux/README.md
@@ -0,0 +1,31 @@
+# Python Development Support Files
+
+This directory contains support files for developing Python demos:
+
+- `requirements.txt`:
+  Requirements for development. Contains dependency for `ruff` (linter & formatter), `mypy` (type checker)
+  and `workbench-typestubs` (typestubs for the `workbench` module). All of these are also installed
+  in the `re.sonny.Workbench.Devel` Flatpak (TODO: not true yet, see below.)
+- `mypy.ini`:
+  Rules for `mypy` used for all demos.
+- `workbench-typestubs`:
+  Python package containing typestubs for the `workbench` package which is available to demos and
+  implements the Workbench API.
+
+## Run type checks.
+
+```sh
+cd python-aux
+pip3 install -r requirements.txt
+cd ..
+# Check single file:
+mypy --config-file python-aux/mypy.ini src/Welcome/main.py
+# Check all:
+mypy --config-file python-aux/mypy.ini src
+```
+
+## TODO
+
+TODO: All requirements should be in the Devel Flatpak, but unsure how the
+typestub itself could be added there...? We might need to put that in an extra repo and add it
+as a module to the Devel Flatpak. Ruff is already in there.
diff --git a/python-aux/mypy.ini b/python-aux/mypy.ini
new file mode 100644
index 00000000..a47f0f90
--- /dev/null
+++ b/python-aux/mypy.ini
@@ -0,0 +1,5 @@
+[mypy]
+warn_unused_configs = True
+explicit_package_bases = True
+namespace_packages = True
+check_untyped_defs = True
diff --git a/python-aux/requirements.txt b/python-aux/requirements.txt
new file mode 100644
index 00000000..9eda497e
--- /dev/null
+++ b/python-aux/requirements.txt
@@ -0,0 +1,4 @@
+./workbench-typestubs
+ruff>=0.3.0
+pygobject-stubs>=2.11.0 --config-settings=config=Gtk4,Gdk4,GtkSource5
+mypy>=1.9.0
diff --git a/python-aux/workbench-typestubs/MANIFEST.in b/python-aux/workbench-typestubs/MANIFEST.in
new file mode 100644
index 00000000..49adbf0c
--- /dev/null
+++ b/python-aux/workbench-typestubs/MANIFEST.in
@@ -0,0 +1,2 @@
+include workbench/py.typed
+recursive-include workbench *.pyi
diff --git a/python-aux/workbench-typestubs/pyproject.toml b/python-aux/workbench-typestubs/pyproject.toml
new file mode 100644
index 00000000..d2f5d48d
--- /dev/null
+++ b/python-aux/workbench-typestubs/pyproject.toml
@@ -0,0 +1,7 @@
+[build-system]
+requires = ["setuptools"]
+build-backend = "setuptools.build_meta"
+
+[project]
+name = "workbench-typestubs"
+version = "46.0.0"
diff --git a/python-aux/workbench-typestubs/workbench/__init__.pyi b/python-aux/workbench-typestubs/workbench/__init__.pyi
new file mode 100644
index 00000000..d95e2873
--- /dev/null
+++ b/python-aux/workbench-typestubs/workbench/__init__.pyi
@@ -0,0 +1,7 @@
+from gi.repository import Gtk, Gio
+
+window: Gtk.Window
+builder: Gtk.Builder
+
+def resolve(path: str) -> Gio.File:
+  ...
diff --git a/python-aux/workbench-typestubs/workbench/py.typed b/python-aux/workbench-typestubs/workbench/py.typed
new file mode 100644
index 00000000..e69de29b
diff --git a/src/Welcome/main.py b/src/Welcome/main.py
index 9b95a029..de0a792f 100644
--- a/src/Welcome/main.py
+++ b/src/Welcome/main.py
@@ -1,3 +1,5 @@
+from typing import cast
+
 import gi
 
 gi.require_version("Gtk", "4.0")
@@ -19,7 +21,7 @@ def dialog_response(dialog, response):
     dialog.close()
 
 
-subtitle_box: Gtk.Box = workbench.builder.get_object("subtitle")
+subtitle_box = cast(Gtk.Box, workbench.builder.get_object("subtitle"))
 
 button = Gtk.Button(label="Press me", margin_top=6, css_classes=["suggested-action"])
 button.connect("clicked", greet)