uplift.page
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prompt🎮 Gamesv2 · updated 2026-06-12

Multiplayer web game

Realtime multiplayer in the browser with PartyKit rooms and client prediction.

Run it as a prompt

Paste this into any AI agent, or fetch it: curl -s https://uplift.page/api/v1/prompts/multiplayer-web-game/raw

prompt.md
# Multiplayer web game

Build a small realtime multiplayer game (2–16 players per room) with authoritative server state and lag that players don't notice under 150ms RTT.

## Recommended stack

- **PartyKit** - room server. One file per room, websockets and state colocated at the edge, deploys in seconds.
- **Phaser 3 or PixiJS** - client rendering. Phaser if you need physics/scenes; Pixi if you only need fast sprites.
- **TypeScript + zod** - protocol. One shared schema file validates every message both directions.
- **Vercel** - client hosting. Static client next to the edge rooms keeps latency budgets honest.

## Build steps

1. Define the wire protocol first: a zod-validated union of client→server intents and server→client snapshots.
2. Make the server authoritative: clients send intents, server simulates at a fixed tick (e.g. 20Hz), broadcasts snapshots.
3. Interpolate remote players between snapshots; predict only the local player, reconcile on snapshot.
4. Add rooms: create/join by 4-letter code; cap players; drop idle connections.
5. Playtest with artificial 150ms delay (Chrome devtools) from day one.

## Watch out for

- Trusting client positions - cheaters and physics divergence both come from this.
- Sending full state every tick at scale; delta-compress or send only changed entities.
- Testing only on localhost where latency is 0ms.

## Definition of done

- Two browsers on different networks stay in sync through a 2-minute session
- A refresh rejoins the same room with state intact
- Server validates every message; malformed input can't crash a room

The full prompt

Build a small realtime multiplayer game (2–16 players per room) with authoritative server state and lag that players don't notice under 150ms RTT.

Recommended stack

  • PartyKit - room server. One file per room, websockets and state colocated at the edge, deploys in seconds.
  • Phaser 3 or PixiJS - client rendering. Phaser if you need physics/scenes; Pixi if you only need fast sprites.
  • TypeScript + zod - protocol. One shared schema file validates every message both directions.
  • Vercel - client hosting. Static client next to the edge rooms keeps latency budgets honest.

Build steps

  1. Define the wire protocol first: a zod-validated union of client→server intents and server→client snapshots.
  2. Make the server authoritative: clients send intents, server simulates at a fixed tick (e.g. 20Hz), broadcasts snapshots.
  3. Interpolate remote players between snapshots; predict only the local player, reconcile on snapshot.
  4. Add rooms: create/join by 4-letter code; cap players; drop idle connections.
  5. Playtest with artificial 150ms delay (Chrome devtools) from day one.

Watch out for

  • Trusting client positions - cheaters and physics divergence both come from this.
  • Sending full state every tick at scale; delta-compress or send only changed entities.
  • Testing only on localhost where latency is 0ms.

Definition of done

  • Two browsers on different networks stay in sync through a 2-minute session
  • A refresh rejoins the same room with state intact
  • Server validates every message; malformed input can't crash a room

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