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PartyKit

Realtime, multiplayer infrastructure — stateful serverless for collaborative apps.

Acquired — still operating

Acquired by Cloudflare (April 2024); still operating and actively developed.

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About

PartyKit is an open-source platform for building realtime, multi-user applications: chat, collaborative editing, multiplayer games, live dashboards, AI agents with shared state. The core idea is stateful serverless — each "room" is a small stateful server (a Party) that holds WebSocket connections and state as if it were a single machine, while the platform handles global distribution. The SDK family covers it end to end: PartyServer (Durable Object base class), PartySocket (auto-reconnecting WebSocket client), Y-PartyServer (Yjs CRDT integration), plus pub/sub, state-sync, and scheduling primitives.

In April 2024 Cloudflare acquired PartyKit, and the bet paid off architecturally: PartyServer is now the foundation of Cloudflare's own Agents SDK (DurableObject → PartyServer → Agent → AIChatAgent), so this isn't abandonware — it's upstream of Cloudflare's agent infrastructure. The repo (~5,700 stars, MIT) stays active.

For developers the pitch is simple: multiplayer sync without standing up socket infrastructure, with Yjs conflict resolution and presence built in. The tradeoff is platform coupling — you're building on Cloudflare's Durable Objects model whether you deploy there or not.

What it can do

  • Stateful rooms: each party holds connections + state like a single machine
  • PartySocket client with auto-reconnect, heartbeat, and missed-message catch-up
  • Y-PartyServer: Yjs CRDT integration for conflict-free collaborative editing
  • Presence, pub/sub (partysub), state sync (partysync), alarms (partywhen)
  • Foundation of Cloudflare's Agents SDK — first-class AI agent support
  • MIT-licensed, ~5,700 GitHub stars, active under Cloudflare

Setup

  1. npm install partykit partysocket in your project.
  2. Define a Party: extend PartyServer with onConnect/onMessage handlers.
  3. Deploy with npx partykit deploy (or run on Cloudflare Workers).
  4. Connect clients with PartySocket (auto-reconnect included); add Y-PartyServer for CRDT sync.

Prerequisites

Node.js 18+; a Cloudflare account for hosted deploys (self-hostable). Familiarity with WebSockets helps.

Use cases

realtimemultiplayerdeveloper-toolswebsocketsserverless

Works with

Trust score — 8/10

/10 trustVerified

Scored 8/10 (verified tier, metrics-v1). Evidence: 5,732 GitHub stars (partykit/partykit); MIT license; repo pushed 2026-10-09; Acquired by Cloudflare April 2024 — verified via Cloudflare blog; PartyServer is now the foundation of Cloudflare's Agents SDK (still operating, actively developed); PartyServer/PartySocket/Y-PartyServer package architecture verified against repo. Manual review: realtime/multiplayer claims verified; platform coupling to Cloudflare Durable Objects model is the real architectural tradeoff. License: MIT.

★ 5,732 GitHub stars

How the trust score is built

Full methodology →
Adoption · stars/downloads, log-scaled vs peers
7.0/10
Maintenance · recency, releases, issue load
8.0/10
Openness · license + docs
10.0/10
Manual review · sanity read + red-flag check
8.0/10
  • · 5,732 GitHub stars (partykit/partykit); MIT license; repo pushed 2026-10-09
  • · Acquired by Cloudflare April 2024 — verified via Cloudflare blog; PartyServer is now the foundation of Cloudflare's Agents SDK (still operating, actively developed)
  • · PartyServer/PartySocket/Y-PartyServer package architecture verified against repo
  • · manual review: realtime/multiplayer claims verified; platform coupling to Cloudflare Durable Objects model is the real architectural tradeoff

Sources

Every fact above was checked against these sources. Where a claim comes from the provider and couldn't be independently verified, the text says so.