The app is built from ES modules, and browsers refuse to load those from
file:// — so opening index.html by double-clicking
it will always land here. Serve the folder over http instead:
cd path/to/guitar-tools python3 -m http.server 8000
Then open http://localhost:8000.
Any static server works: npx serve, php -S localhost:8000,
or a Live Server editor extension.
If you are already on http://, check that the server is
rooted at the folder containing index.html, and hard-reload
to clear a stale cached script.