Keystone

Harmonic mixing analysis for your DJ library. Keystone reads your tracks, works out key, tempo and energy, and lays them out on a Camelot wheel so you can see what mixes with what.

Free, open source, and entirely offline. No account, nothing uploaded.

What it does

• Camelot wheel. Click a key and the library narrows to it plus everything compatible with it.
• Key, tempo, energy on every row, with eight cue markers you can drag on the waveform.
• Honest ambiguity. When the key is genuinely borderline, Keystone shows the pair (8A/8B) rather than committing to a letter it cannot stand behind.
• Write it back. Key, energy and tempo into your tags, your filenames, or both — with a preview before and an undo after.
• Cue export to rekordbox and Traktor. Your collection file is backed up first, and Keystone refuses to write while the app is open.
• Tag cleanup in bulk: global replace, stray spaces, cover art, per-track editing.
• Collections, ratings and search across the whole library.

What it does not do

Stated plainly, because the alternative is finding out later.

• No Serato export yet. rekordbox and Traktor only. Serato writes into the audio files themselves across four container formats, so it comes when it can be tested properly rather than when it compiles.
• No mashup or two-deck view. No stem separation, no acapella extraction.
• No published accuracy number. Keystone makes no accuracy claim, and specifically does not claim to beat Mixed In Key. Any figure would have to be measured on a public annotated set of real audio with the scoring method named, and that has not been done yet. When it is, the number and the method get published together or not at all. There is one measurement in the repository — docs/ACCURACY.md, which reports how often Keystone's key agrees with Mixed In Key's own labels on one private 1,063-track library — and it is agreement between two programs on one DJ's collection, where neither is known to be right, so nothing in it is an accuracy figure or comparable with any published one.
• The confidence scale is not calibrated yet, and you will see that. The thresholds behind the key badge were fitted on synthetic audio and read far too low on real records, so on a real library most tracks currently show the relative pair rather than a single key. The answer underneath is usually sound; the number grading it is not. This is a known defect, not the honest-ambiguity feature working as intended.
• No writing into rekordbox's own database. XML only.
• Nothing for material that is not broadly 4/4 and tempo-stable. Live, acoustic, classical, swung and half-time tracks get a low-confidence result or an honest "could not analyse" — never a confident wrong answer.
• No cloud, in any part of the app. Including models: if something cannot be bundled, it does not ship.

Install

macOS

1. Download the .dmg from keystone.swendl.com or the releases page.
2. Open it and drag Keystone.app to Applications.
3. If macOS says "Keystone is damaged and can't be opened", run this once:

xattr -rd com.apple.quarantine /Applications/Keystone.app

4. Launch it from Applications.

That warning appears because the app is not yet notarized with Apple. The command clears the quarantine flag macOS puts on downloaded files.

Windows

Download and run the installer from the releases page.

First run

1. Click ADD TRACKS and pick a folder.
2. Let the analysis queue work through it — the sidebar shows progress and survives a restart.
3. Click a segment on the wheel to see what mixes with it.

Build from source

You need Node 20+, Rust stable via rustup, and on macOS the Xcode command line tools (xcode-select --install).

npm install
npm run tauri dev      # development, with hot reload
npm run tauri build    # production bundle

Keystone keeps its database in the platform app data directory:

• macOS: ~/Library/Application Support/app.keystone.desktop/keystone.db
• Windows: %APPDATA%\app.keystone.desktop\keystone.db
• Linux: ~/.local/share/app.keystone.desktop/keystone.db

Releasing

Push a version tag and CI builds macOS and Windows and publishes the release:

git tag v0.1.0 && git push origin v0.1.0

License

MIT. See LICENSE.

Keystone is part of a set: Stack for sample libraries, Keystone for harmonic mixing, Capstone for audio correction.