Paste a track and Liner writes its notes: the genres it sits between, what it is built from, how hard it pushes, and the room it belongs in.
or
Liner listens. Your browser decodes the audio and measures it — the tempo from where the transients land, the key from which pitches ring out, the dynamics from how far the loud parts sit above the quiet ones — and the reading is made against those numbers. A file you choose is measured on your own machine and never uploaded.