We have added the support for Neapolitan chords for Roman Numerals notation. You just need to input N in the text field, or N6 if you want to have the most common form that is in its first inversion.
In this example, you can see two Neapolitan chords. They are built from a major triad, whose root note is the lowered second degree of the scale. Here in C major, it is a D flat.