[strogonoff]

There’s a cheap trick to make sure a website that claims to do everything client-side actually does everything client-side:

1. Open the site in an incognito window.

2. Turn off your Internet.

3. Do what you’ve got to do.

4. Close browser window.

As a bonus, and this makes it better than just flipping the offline switch in developer tools, if you turn off Internet in a way that keeps the browser thinking it’s online, you can also peek at whether any network requests are made (for pathological cases where the app does everything locally but phones home anyway).