Duolingo Ninja is a free Chrome add-on developed by Mink. This add-on allows users to learn Duolingo vocabulary while browsing the web. With Duolingo Ninja, users can sync words from Duolingo and choose whether to translate words or sentences. The add-on displays translations on the web pages users visit, allowing them to hover over the translation to see the original text. Users can also spread out translations across the whole page or concentrate on the top. Duolingo Ninja even allows users to ignore certain domains they don't want to translate. Additionally, users can see and copy the vocabulary they've learned with Duolingo.

Duolingo Ninja respects user privacy. While the notice about having access to browsing history and website data may appear, it is automatically generated because the add-on runs on every tab. The add-on does not actually monitor browsing history or require personal information to function properly.