For Navidrome · web and Android
Kultr is a modern, minimalist client for Navidrome. It mirrors your whole library locally, crossfades on two real decks, and beat-matches one track into the next.
No account, no tracking Open source, Apache 2.0 Self-host in a minute
A working demo. Wait for the blend or press next — this whole page takes its colour from the cover, the way the app does.
A look at it
Your library, mirrored locally. Browsing is instant because nothing is fetched to draw it.
What it does
Kultr keeps a copy of your library on the device, so no page waits on the server to draw. And every track plays on one of two decks, so a transition is a real overlap, not a volume trick.
One button copies every artist, album, track, playlist and genre to the device. Browsing, sorting and searching are then instant, and keep working with the server switched off. After that, a check pulls in only what moved — on start-up, hourly, or when you ask.
Two players genuinely overlap, for up to 20 seconds, in four fade shapes. Or switch it off for gapless: the next track starts the instant this one ends.
Beat-matched, key-aware transitions, planned from each track’s tempo, key, energy and structure.
A sync button on every page. Downloads go into the browser, or a folder you pick, named Artist - Album - Track.
Give each one a name, switch between them, and turn one off without deleting it.
The surfaces, the highlights and the backdrop all retint from whatever is playing. Then make it yours: light or dark, three corner styles, six playheads, an accent blended with the artwork’s, and a box for your own CSS.
InjeKt
Kultr decodes each track once and measures it: tempo and beat grid, musical key, loudness and brightness, and where the intro ends and the outro begins. When one track is about to hand over, it plans the transition from those numbers — and shows you the plan.
Beat-matched at 122 BPM — this track down 3.2%, the next up 3.3%
Scroll sideways to see the whole transition.
Rather than drag the new track onto the old one’s tempo, it picks a tempo between them and moves both. Each side moves half as far, which is half as audible — and pairs a one-sided match would reject now work.
The blend starts on a downbeat of the outgoing track and the incoming one enters on a downbeat of its own, so the grids actually line up.
The outgoing bass rolls off before the incoming bass comes up, so two kick drums never fight.
Keys are worked out in Camelot notation. When two clash, it filter-sweeps out of the old track instead of blending into a muddy chord.
The next track comes in at its first real downbeat, not after twenty seconds of ambient pad.
When the queue runs out it keeps going, with tracks chosen by tempo, key and energy, so the set keeps flowing.
Every part degrades gracefully. No analysis yet, tempos too far apart, or no Web Audio — and it quietly becomes a good ordinary crossfade.
The DSP and the mixing rulesGet Kultr
It runs entirely in your browser and connects to your Navidrome. It stores nothing, ships no music and has no backend. Rather not trust a page on the internet with your password? Run it yourself — it takes about a minute.
Open it, sign in to your Navidrome, and press Sync my library. Install it from Chrome or Edge, or with Share → Add to Home Screen on iOS.
A proper Android music app with the same behaviour — crossfade, InjeKt, the library mirror — plus what only a native app can do.
KultrSHA-256 3C:26:16:4A:FD:6F:C1:30:F5:7D:A5:2B:4F:04:AB:2B:E8:3C:89:25:50:89:6F:C9:43:57:D2:E0:B8:51:6F:E0
Already running Navidrome in Docker? Three commands, then open localhost:4180 and leave the server field blank.
$ git clone https://github.com/evropiani/Kultr.git $ cd Kultr $ docker compose up -d
A native iOS app is planned; until then Kultr installs from Safari as a web app. Settings exported from one Kultr open in the other. What’s new
Your data
No analytics, no telemetry, no third-party requests, no fonts from anyone’s CDN. This website keeps the same rule.
Every part of Kultr — the Subsonic client, the two-deck audio engine, the tempo and key detection, the interface, the tests and the install guides — was produced by prompting Claude Code rather than typed by hand. It’s a fair thing to disclose. So was this website.
Open Kultr, point it at your Navidrome and press Sync my library. It only has to happen once.