MagiWords highlights every word on a page by how well you know it, saves the ones you want with the sentence you met them in, and brings them back when you are about to forget.
A definition tells you what a word means. The sentence you actually met it in is what makes it stick — so MagiWords keeps that sentence and quizzes you on it, instead of asking you to memorise a list detached from anything you read.
It also understands word forms: run, running and ran are one entry in your vocabulary, not three.
No account, no server, no analytics. Your words, scores and settings live in your own browser and are never sent anywhere.
MagiWords asks for no access to any website when you install it — it can read a page only at the moment you invoke it, and only that tab. If you leave dictionary lookup on, the single word is sent to fetch its meaning; never the sentence, never the page you were reading. You can switch that off and it works entirely offline.