Design a collaborative live party playlist app

Design a real-time collaborative social playlist and music queueing application for house parties, road trips, and social gatherings where all guests can participate without fighting over the aux cord.

Context

Parties suffer from the "Aux Cord Tyrant" (one person playing only their music), guest songs getting skipped abruptly, and dead air between tracks.

Clarifying questions to ask first

Does every guest need a paid Spotify account to vote? (No, host hosts the session; guests join via free web link).
Is there cross-fading and automated transition between songs? (Yes).

How to approach it

Map Party Dynamics: The Host (owns speakers, wants party energy maintained), The Party Guests (want their favorite tracks played without begging the host), The Vibe Killer (queues obscure slow songs)
Design Core Real-Time Social Music Mechanics:
1. 1-Tap QR Code Guest Join (Zero app download required via web app / Spotify Session)
2. Democratic Song Upvoting & Downvoting Queue (Songs with most guest upvotes move up in queue automatically)
3. "Vibe & BPM Guardrail" (Host sets energy floor: app blocks slow acoustic ballads during high-energy dance hours)
4. "Fair-Share Queueing Algorithm" (Prevents one guest from queueing 10 songs in a row)
Define Engagement and Session Duration Metrics

Framework: Party Social Dynamics & Aux Cord Friction -> Frictionless QR Guest Onboarding -> Democratic Voting & Queueing Algorithm -> Host Vibe Controls -> Metrics

Sample answer

Requiring guests to download an app kills participation; a lightweight web-app QR join ensures 100% room participation
An automated fair-share queue algorithm prevents any single user from dominating the party music

MVP: Host launches session on speaker, guests scan table QR code to search and upvote tracks, automated democratic queue plays highest-voted song next, host retains instant skip veto

Executive design: A democratic party music queue where guests scan a QR code to search and upvote songs in real-time, protected by fair-share queue algorithms and host vibe guardrails.

What interviewers look for

Frictionless Guest Onboarding (QR Join)
Democratic Queueing & Upvote Mechanics
Vibe Protection & Fair-Share Queueing Algorithms
Host Control & Veto Powers