Unzip it somewhere permanent — Applications or Documents. Not Downloads, or it may get cleaned up later.
Double-click install.command
If macOS says "unidentified developer": right-click the file → Open → Open again. One time only.
A black window installs everything. Wait for "Setup complete" — the audio tools take a few minutes on the first run.
Add it to Chrome:
Go to chrome://extensions
Turn on Developer mode (top-right)
Click Load unpacked
Pick the extension folder inside the unzipped folder
The helper starts on its own every time you log in — nothing to launch.
Using it
Copy a YouTube link, click the extension, paste, hit Download MP3. You get a 320 kbps MP3 in Downloads plus:
Key: D minor • Camelot: 7A • BPM: 117.5
Autotune — set your plugin to D minor
Notes to snap to: D E F G A A# C
(same notes as F major)
Set your plugin to that key, or manually enable just those notes. The "same notes as" line is there because some plugins only list major keys — D minor and F major have identical notes, so either works.
Worth knowing
About 73% accurate on the exact key, 82% on the right scale — the one that matters for autotune, since relative keys share notes.
Not 100%, and no tool is. Some songs change key partway through. Even Tunebat gets those wrong — Spotify's data calls Eminem's Lose Yourself D major when the sheet music says D minor.
Trust your ear. If the key fights the vocal, try the relative key on the "same notes as" line.
More accurate on isolated vocals or instrumental stems than full masters — bass and drums muddy the pitch detection.