Drop a sound on each of the eight slots and save. You get a kit folder for the NT's card, with every file named and converted the way the Performer Drums plug-in expects. Everything happens in your browser; no file is uploaded anywhere.
Drop several sounds anywhere on the page and they go to the slots their names point to (kick, snare, hh…), the rest into free slots. Drop on a slot to put a sound exactly there.
Put the kit folder in the card's samples folder, or a folder inside it such as samples/Performer Drums. The NT looks for new samples when it starts, so restart it after adding a kit.
16-bit WAV files, named 1KIK-012.wav, 5SNR-012.wav and so on, so each lands on its voice. Pitch, decay, drive and the rest are set on the NT and saved in its presets.
WAV and AIFF in any browser; MP3, FLAC, Ogg and others where the browser can decode them. "Save to card" needs Chrome or Edge; other browsers download a zip instead.