There's no third party! It's all in your browser.
You download basically a few bloom filters for low-entropy 1-grams, 2-grams, and 3-grams, and there's some highly optimized Javascript to do probabilistic matches.
You download basically a few bloom filters for low-entropy 1-grams, 2-grams, and 3-grams, and there's some highly optimized Javascript to do probabilistic matches.
No personal offense intended, that is a genuine problem with your approach.
Once you've loaded all the 3-grams (~50MB of data), you can run entirely offline, close the page, and then go back online.
Then try your password.
Alternate solution: load the web page and then turn off your WiFi while you test it.