🎛️ Free & Open Source · macOS · 100% On-Device — Nothing Uploaded
Kymata Labs · Open Source
BPM & Key Detection That Never Leaves Your Mac.
Drop in any track. TempoKey analyzes the whole song offline and shows the overall tempo and key — plus exactly how each one drifts across the song on a shared timeline. Private by design, free forever.
Free · Open source (Swift) · macOS 14+ · No account, no upload, no telemetry
From Track to Timeline in Seconds
Download & Build
Clone the open-source repo, run xcodegen, and open it in Xcode. macOS 14+, Xcode 15+.
Drop a Track
Drag any audio file onto the drop zone, or use Choose File. Analysis starts immediately, offline.
Read the Timeline
See the overall BPM and key up top, and exactly how each moves through the song below.
What You See
The overall read up top — and the story underneath it.
Tempo
124BPM
Key
A minor
8A · circle of fifths
Tempo across the song
Key ribbon (fainter = less certain)
A single average says "124 BPM." TempoKey shows you the build-up at 0:48 and the half-time bridge — the parts that matter for a mix.
Built for People Who Trust Their Ears
Whole-Song Analysis
Not just one average number. TempoKey shows how tempo and key drift across the entire track on a shared timeline.
100% On-Device
All decoding and analysis runs offline on your Mac using AVFoundation + Accelerate/vDSP. Nothing is ever uploaded.
Tempo Timeline
A live BPM curve reveals where a track speeds up, drops, or drifts — the moments a single number hides.
Key Ribbon
A circle-of-fifths-colored key ribbon, fainter where the estimate is less certain, so you can trust it at a glance.
Beat Markers
Beat tick marks overlay the timeline so you can see the grid the detector locked onto, not just the result.
Every Format
Drag in mp3, m4a/aac, wav, aiff, caf, flac and more. Light 'paper' or dark mode, your choice.
Why TempoKey
Web BPM tools want your file on their server. Plugins want your DAW open. TempoKey wants nothing — no account, no upload, no subscription. It runs the analysis on your machine, shows you the whole song instead of one number, and the source is right there on GitHub if you want to see exactly how it decides.
Architecture: a UI-free Swift core (TempoKeyCore) handles AVFoundation decoding, a Swift port of Beat-and-Tempo-Tracking (Accelerate/vDSP FFT), and on-device key estimation. Free and open source under the Kymata Labs umbrella.
Frequently Asked Questions
Does TempoKey upload my audio anywhere?
No. Every step — decoding, beat/tempo detection, and key estimation — runs locally on your Mac. No file ever leaves your machine, and TempoKey works with no internet connection at all.
Is it really free?
Yes. TempoKey is free and fully open source on GitHub. There is no paywall, account, or telemetry. Build it yourself or read exactly how it works.
Why show tempo and key across the whole song?
Most tools give you one BPM and one key. Real tracks drift — a build-up accelerates, a bridge modulates. TempoKey plots both on a shared timeline so you see the structure, not just an average that hides it.
What's under the hood?
A UI-free Swift core (TempoKeyCore): AVFoundation for decoding, a Swift port of Beat-and-Tempo-Tracking using Accelerate/vDSP for the FFT, and an on-device key estimator. The app layer is a thin SwiftUI shell.
Who is it for?
DJs setting up harmonic mixes, producers checking a reference, music students learning by ear, and anyone who wants fast, private BPM and key without uploading their library to a web tool.
Try It On Your Own Library
Free, open source, and entirely on your Mac. Build it from source and analyze your first track in minutes.
View on GitHubA Kymata Labs open-source project · kymatalabs.com