Best viewed/operated on a laptop or desktop computer for full functionality.
Nothing is uploaded. The app does not even request any cookies. All action takes place on your local machine. Load an audio file (WAV/MP3/OGG/M4A... and possibly other formats too) via the Open button, or drag/drop it onto the loop area. This should be a fairly short audio file (like typically a few bars of drumming) for best results: though the app won't try and stop you from loading larger files such as entire songs, this is not what it was designed for and results may be unexpected.
The sound does not necessarily have to be drums, as long as there are rhythmic/impulsive events in it. In fact most samples of instrumental phrases, or even speech, will fit the bill. But a sample of a steady-state drone, or something of that nature, is not really suitable. The app will attempt to divide your audio file into segments based on the transients it can find. Turn the Threshold slider up to capture more transients, or down to reject transients below a certain threshold.
Click on a segment to audition it in isolation. Move the L and R indicators to change the loop points if needed. Press the Play button (or use the space bar) to preview or pause the entire loop. You can move the slice markers around for a better fit, add them manually to the waveform with shift-click and delete them by hovering over the marker with the mouse and pressing the delete key.
Use the Save button to export a zip file containing your slices in separate WAV files, plus an SFZ file that can be used in a number of software samplers (the author uses Linuxsampler), and a MIDI file that retains the timing and tempo of your edited loop. This exported zip file is manufactured with the help of JSZip.
(Tip: SFZ files are just text in a simple markup language. If you wanted to, you could tweak them further by hand, or use the free editor sfZed to edit them.)
This app's source code is on Github. Original contributions by myself licensed under the MIT license; all third party code provided as licensed by its original authors.
Waveform view and playback powered by wavesurfer.js, licensed under https://creativecommons.org/licenses/by/3.0/deed.en_US, with modifications by myself.