Just a tool that displays an English word for you to try and remember the Japanese translation, write it somewhere and check if you were correct or not. You can check the stroke order, show furigana before revealing the word to help with (countless…) synonyms, and keep track of how well you are doing with Recalled and Struggling buttons.
You can also just use it as a quick and stress-free Extra Study tool that randomly displays all WaniKani vocabulary, up to Lv11 for now – but I’ll keep adding levels as I’m making progress 