The course is a single file. Open it and it runs. No account, no sign-in, and nothing to reach for.
It works on a plane. It works in a dead spot on the road between Kingston and Port Antonio. It works in five years when the company that made it has stopped answering email, because there is nothing to shut off.
Your progress lives in your own browser. Your lesson history, your review deck, your streak: on the device, not on a machine somewhere else. There is no database with your name in it because there is no database.
Progress does not follow you between devices on its own. Clearing your browser data clears your progress. Those are real limits and they are the price of the arrangement above.
The typefaces are inside the file rather than fetched from Google, and the build refuses to finish if a font link creeps back in. The test suite loads the app and fails if it makes a single network request. The diagnostics that help report a bug hold their notes in memory and send them nowhere — no background request, no beacon on the way out. Forty-one tests exist to keep that true, and they run on every build.
The AI tutor. A conversation partner has to reach a model somewhere, and voice has to be generated somewhere, so that part goes through a proxy holding metered access. It is a separate subscription and it is off unless you turn it on. With it off, the app behaves exactly as described above.
The pronunciation check is not part of that. It runs on the device under every setting, paid or free, and there is a test that fails the build if it ever starts fetching anything.