I built Setflow https://www.setflow.app to solve my own problem, but I'm sure others have the same issue so sharing it here. I got back into DJing after 15+ years and realised I was spending more time organising playlists and trying to find tracks than actually mixing. What started as a small webapp to help myself turned into something usable for others.
What it does:
"Tell me the vibe. I'll build the set."
Imports your Rekordbox library (XML export).
Generates harmonically mixed playlists using Camelot wheel logic.
BPM matching with smooth tempo transitions (±3% between tracks).
Energy profiles: Journey, Peak Time, Warm Up, Chill, Cool Down for overall mood.
Intelligent key progression with directional movement around the Camelot wheel.
Exports back to M3U8 or Rekordbox XML format for a pre-built mix.
Firstly, for myself it was time. After amassing a large library over years I often ended up staring at what music to select, never mind understanding if it would sound great together. I just wanted to mix after being out of it for years.
This then evolved into building in harmonic mixing (playing tracks in compatible musical keys) making transitions sound smooth instead of clashing. I found that manually sorting hundreds of tracks by key and planning a set that flows well was tedious and time consuming. Rekordbox has a "Related Tracks" feature but it doesn't build you an actual runnable set with energy progression.
Setflow gives you a starting point playlist that works harmonically and follows an energy curve, so you spend your limited practice time actually mixing instead of dragging tracks around. Combined with playlist history and custom set generation you have flexibility to create, augment and move tracks around based on your output.
Tech stack:
Next.js 16 (App Router)
React 19, Tailwind CSS 4
PostgreSQL 17 + Drizzle ORM
BetterAuth (email/password with verification)
Stripe for payments
Resend for email
Zustand with localStorage persistence
Self-hosted on VPS
Smart Rekordbox importing with track de-duplication.
Drag & drop reordering with visual feedback.
Playlist Builder with smart harmonic suggestions.
Transition notes explaining why each transition works.
Set history and management.
Mobile responsive.
Look, pro DJs mostly already have this skill, but this is squarely aimed at:
Bedroom DJs with large libraries and limited time
Beginners who don't yet have an intuition for what tracks work together
Anyone who wants a quick starting point for set prep. Old dads like me with limited time.
Free tier available to jump in with some limits. Hobby tier at £2.99/month. Pro at £4.99/month for larger libraries.
Would love feedback from any DJs or music nerds here. Happy to answer questions and can offer some free passes in exchange for genuine feedback.