Custom Vocab lets you create vocabulary lists with words (or phrases) and translations between any two languages. You can test yourself on the lists you create, both from the word to the translation and the translation to the word. You can also add context information to the words you create. For example, if you want to add the words for "orange" the color and "orange" the fruit, you can add this context and it will appear in parentheses. Other uses of the context feature include indicating whether a word is masculine, feminine, or plural and indicating whether a word is formal or informal.

Custom Vocab is different from flashcard applications in that it makes you recall the words and translations. The app makes you type in the correct answer and then checks you, keeping track of your score and allowing you to see what you got right, what you got wrong, and what you skipped at the end of each test.