Games · Intermediate
Authoritative Multiplayer Game Server
Build a top-down .io game with a server-authoritative loop, client prediction, and reconciliation so cheating and lag both lose.
You build a browser-based top-down multiplayer game where a Node.js server owns all game state and runs a fixed-rate tick loop, while clients render smooth motion through local prediction and reconcile with server snapshots on arrival. This architecture eliminates the most common multiplayer exploits because clients never trust themselves, and it teaches you the real techniques used in production .io games. By the end you will have a working arena where multiple players move, collide, and see each other in near-real-time across a WebSocket connection deployed to Fly.io.
What you build
- Fixed-rate authoritative server tick loop (20 Hz) that owns all positions, health, and collision resolution
- WebSocket room management via Colyseus with automatic state sync and delta compression
- Client-side prediction so local movement feels instant despite network round trips
- Server reconciliation that replays unacknowledged inputs when a correction arrives from the server
- HTML5 Canvas renderer with interpolation between server snapshots for smooth visuals
- Simple top-down arena with player spawning, movement, and basic projectile shooting
- Fly.io deployment with a persistent WebSocket-compatible machine
What it teaches
- Server-authoritative game architecture and why it prevents client-side cheating
- Fixed-rate game loop design and how tick rate affects bandwidth and feel
- Client-side prediction and the input sequence numbering pattern
- Snapshot reconciliation by replaying unacknowledged inputs over a corrected server state
- Colyseus schema-based state synchronization and delta encoding over WebSockets
- Deploying a stateful WebSocket server to Fly.io with persistent TCP connections
How it works
- 1
Player Input
- Browser captures WASD / mouse
- Input tagged with sequence number
- Sent to server via WebSocket
↓ Client also applies input locally (prediction)
- 2
Server Tick (20 Hz)
- Drains input queue
- Resolves collisions
- Updates authoritative state
- 3
Snapshot Broadcast
- Server sends delta snapshot
- Includes last processed seq number
- All connected clients receive it
- 4
Client Reconciliation
- Discard confirmed inputs
- Replay pending inputs over server state
- Smooth interpolation for other players
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Take it further
- Add lag compensation on the server: record a rolling history of world snapshots and rewind state to a client's estimated render time before processing hit detection.
- Introduce rooms with a matchmaker that groups players by skill rating stored in a Postgres table, and keep a live leaderboard synced through a Colyseus broadcast channel.
- Replace Canvas rendering with a Pixi.js scene graph and add sprite sheets, screen shake on hit, and a minimap overlay.
