Drop an audio file in and read its tempo, its musical key and its Camelot number. Playlist curators, DJs and sync supervisors all ask for these two numbers, and stores show them on your track page — so it is worth knowing them before you fill in a single form.
Everything here runs inside your browser. Your audio is never uploaded, stored or sent anywhere, and no account is needed. Tempo and key are estimated from the audio itself — treat them as a very good first answer, not as a replacement for your own ears.
Editorial and algorithmic playlists are built around energy and pace. When you pitch a track, stating the tempo tells the person reading where it can sit in a sequence without them having to open the file. DJs need it to plan a set, and sync libraries index by it. Getting it wrong by double or half is the most common mistake — a track at 140 is often filed as 70, and both can be defensible, so check the number against how you actually count the track.
Harmonic mixing puts neighbouring keys next to each other so a transition does not clash. The Camelot number exists for exactly that: 8A sits happily beside 7A, 9A and 8B. If you want your track played in sets, or placed next to a specific release, the key is the number that decides whether it fits. It is also what a remixer asks for first.
Your browser decodes the audio, measures how much new energy appears in each short slice of the file, and looks for the spacing that repeats most strongly — that spacing is the tempo. For key, it measures how much energy sits on each of the twelve pitch classes across the whole track and compares that shape against the profiles of all twenty-four major and minor keys. Both are estimates. A track with a sparse or rubato arrangement will be harder to read than a four-to-the-floor one, which is why the second and third best answers are shown too.