This free tool allows you to study Japanese JLPT Flashcards using the web and offers you the ability to change the font size and opacity of the flashcard.  The Japanese flashcard will appear at the bottom right of the page. You can open your vocabulary list or vocabulary word in the right pane.

There are two pages for each flashcard (1 for N1, the other for N5). It's easy to navigate—you can use the left and right buttons to flip the page. If you click on the card, you will see its definition and the pronunciation in a word-by-word format. Also, the definition is written in text, and the meaning is given. Each vocabulary has multiple levels.

Each word has the spelling in the left pane and the pronunciation in the right pane. Likewise, you can open the pronunciation in a word-by-word format.

In addition, you have an option to change the font size. 

You can remove a flashcard by clicking the X button, or add a flashcard by dragging it from the right pane.