To preview this locally, start a static web server in this directory, using any method you like.
For example:
python3 -m http.server 4000 -d public_html/
Then navigate to http://localhost:4000/.
To lint the Python helper script:
pip install tox
tox -v
rsync -av -e ssh --exclude=".DS_Store" public_html/ timotijhof.net:domains/timotijhof.net/treasure21-sub-public_html/