TempoTango - BPM & Key Analyzer

About

TempoTango is a fast, private BPM and key analyzer for tracks playing in your browser tab.

Open the popup, hit Listen, and in about 40 seconds you'll get:
  • BPM (with octave correction so 70/140 confusion is rare)
  • Musical key in standard notation
  • Camelot wheel position for harmonic mixing
  • A confidence indicator on each reading

Built for DJs who use SoundCloud to dig for tracks and want a quick read on whether something fits the set they're building.

What makes TempoTango different
  • Audio is analyzed locally in your browser using essentia.js (WebAssembly). Nothing is uploaded — not the audio, not the result, not even the track URL.
  • No accounts, no signups, no paywalls.
  • No analytics, no telemetry, no third-party services.
  • Works on any track that plays in your active tab — including private and unreleased uploads you have access to.

How it works
  1. Play a track on SoundCloud.
  2. Click the TempoTango toolbar icon.
  3. Hit Listen. The extension captures ~40 seconds of audio from the tab and runs BPM + key detection on-device.
  4. Read the result. Hit "Analyze again" if you want a second pass.

Permissions
  • Tab capture — to read the audio of the tab you're listening to (only when you click Listen).
  • Offscreen — to run audio analysis off the service worker.
  • Active tab — to confirm the tab you're on.
  • Storage — to remember the most recent result while the browser is open.
  • soundcloud.com host access — the extension only operates on SoundCloud.

Open source: TempoTango is AGPL-3.0 (and bundles essentia.js, also AGPL-3.0). Full corresponding source: https://gitlab.com/alexhewittx77/tempo-tango-extension