Key & BPM Finder

Find the key and tempo of any song

Knowing the key and tempo of a track is useful for almost every kind of musician. DJs use it to plan harmonic mixes, producers need it to add samples or vocals that fit, singers use it to pick a comfortable pitch, and players want to know which scale to improvise over. This Key & BPM Finder reads an audio file you already have on your device and estimates both values in a few seconds. It shows the key name (for example A minor), its Camelot code, the relative key, a confidence score and the tempo in beats per minute, plus the half-time and double-time alternatives that tempo detectors commonly confuse.

How the analysis works

The file is decoded with the Web Audio API and mixed down to mono. For key detection, the audio is split into short overlapping frames and each frame is passed through a fast Fourier transform. The energy of every frequency bin is folded into one of the twelve pitch classes (C, C♯, D … B), producing a chromagram that describes how much each note is used throughout the song. That twelve-value profile is then compared with the Krumhansl–Schmuckler key profiles — listener-derived weightings of how strongly each scale degree belongs to a major or minor key — for all 24 keys. The key with the highest correlation wins, and the gap to the runner-up feeds into the confidence score. The chromagram chart lets you see which notes dominate the recording.

Tempo is estimated separately with the open-source web-audio-beat-detector library. It low-pass filters the signal to emphasise kick drums and bass, finds strong peaks, measures the intervals between them and picks the most common interval, which is converted to beats per minute.

Tips for reliable results

Automatic key detection is an estimate, not a certainty. Songs that modulate, use modal harmony or are mostly percussion are harder to classify, and a major key is easily confused with its relative minor because they share the same notes. When the confidence is low, listen to the track, check the alternatives listed below the result and trust your ears. For tempo, compare the result with the half- and double-time values and tap along if needed. Everything runs locally: the file is never uploaded, so you can analyse unreleased mixes and private recordings with complete peace of mind.