KANTAN Chord is a free browser extension developed by doco that allows users to convert chords from various chord sites to their "degrees," also known as Nashville Numbers. This extension is compatible with popular chord sites such as ULTIMATE GUITAR TABS, U-フレット, 楽器.me, J-Total Music, and Guitarians.com.

To use KANTAN Chord, simply open the chord web page and choose the KANTAN Chord icon from the browser extensions. This will open a pop-up window where you can select from three options: "C,F,G" (original), "I,IV,V" (roman numerals), or "1,4,5" (degrees).

The "C,F,G" option displays the chords in their original form and allows you to change keys. The "I,IV,V" option displays the chords' degrees in standard roman numerals format. The "1,4,5" option displays the chords' degrees in numbers, following the "KANTAN Chord" system based on the Nashville Number System.

KANTAN Chord also automatically analyzes the song's key and displays it in the pop-up window. It can detect key changes during a song and indicate them with additional banners. Users can choose keys outside of the auto-analyzed key and adjust the key analyzation sensitivity if needed.

In addition, KANTAN Chord offers various options for customization, such as disabling automatic loading, hiding the key display, and modifying the representation of half tones and minor chords. There is also a beginner mode that simplifies chords for users who are just starting out.

Overall, KANTAN Chord is a convenient browser extension for musicians and guitarists, providing an easy way to convert chords to Nashville Numbers and customize the chord display according to individual preferences.