Multiplayer Game

IMPORTANT: Before doing anything, you MUST read BASE_SKILL.md in this skill's directory. It contains essential guidance on debugging, error handling, state management, deployment, and project setup. Those rules and patterns apply to all RivetKit work. Everything below assumes you have already read and understood it.

Patterns for building multiplayer games with RivetKit, intended as a practical checklist you can adapt per genre.

Starter Code

Start with one of the working examples on GitHub and adapt it to your game. Do not start from scratch for matchmaking and lifecycle flows.

Server Simulation

Game Loop And Tick Rates

Physics

Start with custom kinematic logic for simple games. Switch to a full physics engine when you need joints, stacked bodies, high collision density, or complex shapes (rotated polygons, capsules, convex hulls, triangle meshes).

Pick one engine per simulation. Keep frontend-only libs out of backend simulation paths and treat server state as authoritative.

Spatial Indexing

For non-physics spatial queries, use a dedicated index instead of naive O(n^2) checks:

Networking & State Sync

Netcode

Realtime Data Model

• Snapshots and diffs: Publish state as events. Send a full snapshot on join/resync, then per-tick diffs for regular updates.
• Batch per tick: Keep events small and typed. Batch high-frequency updates per tick.
• Avoid UI framework state for game updates: Use requestAnimationFrame or a Canvas/Three.js loop for simulation, not React state. Reserve UI framework state for menus, HUD, and forms.
• Broadcast vs per-connection: Use c.broadcast(...) for shared updates and conn.send(...) for private/per-player data.

Shared Simulation Logic

Shared simulation logic runs on both the client and the server. For example, an applyInput(state, input, dt) function that integrates velocity and clamps to world bounds can run on the client for prediction and on the server for validation.

• Hybrid modes: Client runs shared movement as primary authority, server runs it for anti-cheat validation.
• Server-authoritative modes: Client uses shared logic for interpolation and prediction only.
• Keep it pure: Movement integration, input transforms, collision helpers, and constants only.
• Put shared code in src/shared/: Keep deterministic helpers in src/shared/sim/* with no side effects.

Interest Management

Control what each client receives to reduce bandwidth and prevent information leaks.

Per-Player Replication Filters

• Filter by relevance: Send each client only state relevant to that player (proximity, line-of-sight, team, or game phase).
• Shooters and action games: Limit replication by proximity and optional field-of-view checks.
• Server-side only: Clients should never receive data they should not see.

Sharded Worlds

• Partition large worlds: Use chunk actors keyed by worldId:chunkX:chunkY.
• Subscribe to nearby chunks: Clients connect only to nearby partitions (for example a 3x3 chunk window).
• Use sparingly: Only when the world is large and state-heavy (sandbox builders, MMOs), not as a default for small matches.

Backend Infrastructure

Persistence

• In-memory state: Best for realtime game state that changes every tick (player positions, inputs, match phase, scores).
• SQLite (rivetkit/db): Better for large or table-like state that needs queries, indexes, or long-term persistence (tiles, inventory, matchmaking pools). Serialize DB work through a queue since multiple actions can hit the same actor concurrently.

Matchmaking Patterns

Common building blocks used across the architecture patterns below.

Actor Topology

Queueing Strategy

• Multiple players can hit the matchmaker at the same time, so actions like find/create, queue/unqueue, and close need to be serialized through actor queues to avoid races.
• Match-local actions (gameplay, scoring) do not need queueing unless they write back to the matchmaker.

Security And Anti-Cheat

Start with this baseline, then harden further for competitive or high-risk environments.

Baseline Checklist

• Identity: Use c.conn.id as the authoritative transport identity. Treat playerId/username in params as untrusted input and bind through server-issued assignment/join tickets.
• Authorization: Validate the caller is allowed to mutate the target entity (room membership, turn ownership, host-only actions).
• Input validation: Clamp sizes/lengths, validate enums, and validate usernames (length, allowed chars, avoid unbounded Unicode).
• Rate limiting: Per-connection rate limits for spammy actions (chat, join/leave, fire, movement updates).
• State integrity: Server recomputes derived state (scores, win conditions, placements). Never allow client-authoritative changes to inventory/currency/leaderboard totals.

Movement Validation

For any mode with client-authoritative movement (hybrid flows), clients may send position/rotation updates for smoothness, but the server must:

• Enforce max delta per update (speed cap) based on elapsed time.
• Reject or clamp teleports.
• Enforce world bounds (and basic collision if applicable).
• Rate limit update frequency (for example 20Hz max).

Architecture Patterns

Each game type below starts with a quick summary table, then details actors and lifecycle.

Battle Royale

Actors

• Key: matchmaker["main"]

• Responsibility: Finds or creates lobbies, tracks pending reservations, and maintains occupancy.

• Actions

  • findMatch
  • pendingPlayerConnected
  • updateMatch
  • closeMatch

• Queues

  • findMatch
  • pendingPlayerConnected
  • updateMatch
  • closeMatch

• State

  • SQLite
  • matches
  • pending_players
  • player_count includes connected and pending players

• Key: match[matchId]

• Responsibility: Runs lobby/live/finished phases, owns player state, zone progression, and eliminations.

• Actions

  • connect
  • Movement and combat actions

• Queues

  • None

• State

  • JSON
  • phase
  • players
  • zone
  • eliminations
  • snapshot data

Lifecycle

sequenceDiagram
	participant C as Client
	participant MM as matchmaker
	participant M as match

	C->>MM: findMatch()
	alt no open lobby
		MM->>M: create(matchId)
	end
	MM-->>C: {matchId, playerId}
	C->>M: connect(playerId)
	M->>MM: pendingPlayerConnected(matchId, playerId)
	MM-->>M: accepted
	Note over M: lobby countdown -> live
	M-->>C: snapshot + shoot events
	M->>MM: closeMatch(matchId)

Arena

Actors

• Key: matchmaker["main"]

• Responsibility: Runs mode queues, builds full matches, assigns teams, and publishes assignments.

• Actions

  • queueForMatch
  • unqueueForMatch
  • matchCompleted

• Queues

  • queueForMatch
  • unqueueForMatch
  • matchCompleted

• State

  • SQLite
  • player_pool
  • matches
  • assignments keyed by connection and player

• Key: match[matchId]

• Responsibility: Runs match phases and in-match player/team state for score and win conditions.

• Actions

  • connect
  • Gameplay actions

• Queues

  • None

• State

  • JSON
  • phase
  • players
  • team assignments
  • score and win state

Lifecycle

sequenceDiagram
	participant C as Client
	participant MM as matchmaker
	participant M as match

	C->>MM: queueForMatch(mode)
	Note over MM: enqueue in player_pool
	Note over MM: fill when capacity reached
	MM->>M: create(matchId, assignments)
	Note over MM: persist assignments
	MM-->>C: assignmentReady
	C->>M: connect(playerId)
	Note over M: waiting -> live when all players connect
	M->>MM: matchCompleted(matchId)

IO Style

Actors

• Key: matchmaker["main"]

• Responsibility: Routes players into the fullest open lobby and tracks reservations and occupancy.

• Actions

  • findLobby
  • pendingPlayerConnected
  • updateMatch
  • closeMatch

• Queues

  • findLobby
  • pendingPlayerConnected
  • updateMatch
  • closeMatch

• State

  • SQLite
  • matches
  • pending_players
  • Occupancy includes pending reservations

• Key: match[matchId]

• Responsibility: Runs per-match movement simulation and broadcasts snapshots.

• Actions

  • connect
  • setInput

• Queues

  • None

• State

  • JSON
  • players
  • inputs
  • movement state
  • snapshot cache

Lifecycle

sequenceDiagram
	participant C as Client
	participant MM as matchmaker
	participant M as match

	C->>MM: findLobby()
	alt no open lobby
		MM->>M: create(matchId)
	end
	MM-->>C: {matchId, playerId}
	C->>M: connect(playerId)
	M->>MM: pendingPlayerConnected(matchId, playerId)
	MM-->>M: accepted
	Note over M: fixed tick simulation
	M-->>C: snapshot events
	M->>MM: closeMatch(matchId)

Open World

Actors

• Key: chunk[worldId,chunkX,chunkY]
• Responsibility: Owns chunk-local players, blocks, movement tick, and chunk membership.
• Actions
  • connect
  • enterChunk
  • addPlayer
  • setInput
  • leaveChunk
  • removePlayer
• Queues
  • None
• State
  • JSON
  • connections
  • players
  • blocks scoped to one chunk key

Lifecycle

sequenceDiagram
	participant C as Client
	participant CH as chunk

	Note over C: resolve chunk keys from world position
	loop each visible chunk
		C->>CH: connect(worldId, chunkX, chunkY, playerId)
		Note over CH: store connection metadata
	end
	C->>CH: enterChunk/addPlayer
	loop movement updates
		C->>CH: setInput(...)
		CH-->>C: snapshot
	end
	C->>CH: leaveChunk/removePlayer or disconnect
	Note over CH: remove membership and metadata

Party

Actors

• Key: matchmaker["main"]

• Responsibility: Handles party create/join flow, validates join tickets, and tracks party size.

• Actions

  • createParty
  • joinParty
  • verifyJoin
  • updatePartySize
  • closeParty

• Queues

  • createParty
  • joinParty
  • verifyJoin
  • updatePartySize
  • closeParty

• State

  • SQLite
  • parties
  • join_tickets for party lookup and join validation

• Key: match[matchId]

• Responsibility: Owns party members, host role, ready flags, and phase transitions.

• Actions

  • connect
  • startGame
  • finishGame

• Queues

  • None

• State

  • JSON
  • members
  • host
  • ready state
  • phase
  • party events

Lifecycle

Host Flow

sequenceDiagram
	participant H as Host Client
	participant MM as matchmaker
	participant M as match

	H->>MM: createParty()
	MM-->>H: {matchId, partyCode, playerId, joinToken}
	H->>M: connect(playerId, joinToken)
	M->>MM: verifyJoin(...)
	MM-->>M: allowed
	M->>MM: updatePartySize(playerCount)
	H->>M: startGame() / finishGame()
	M->>MM: closeParty(matchId)

Joiner Flow

sequenceDiagram
	participant J as Joiner Client
	participant MM as matchmaker
	participant M as match

	J->>MM: joinParty(partyCode)
	MM-->>J: {matchId, playerId, joinToken}
	J->>M: connect(playerId, joinToken)
	M->>MM: verifyJoin(...)
	MM-->>M: allowed / denied
	M->>MM: updatePartySize(playerCount)

Ranked

Actors

• Key: matchmaker["main"]

• Responsibility: Runs rating-based queueing, pairing, assignment persistence, and completion fanout.

• Actions

  • queueForMatch
  • unqueueForMatch
  • matchCompleted

• Queues

  • queueForMatch
  • unqueueForMatch
  • matchCompleted

• State

  • SQLite
  • player_pool
  • matches
  • assignments with rating window and connection scoping

• Key: match[matchId]

• Responsibility: Runs ranked match phase, score, and winner reporting.

• Actions

  • connect
  • Gameplay actions

• Queues

  • None

• State

  • JSON
  • phase
  • players
  • score
  • winner
  • completion payload

• Key: player[username]

• Responsibility: Stores canonical player MMR and win/loss profile.

• Actions

  • initialize
  • getRating
  • applyMatchResult

• Queues

  • None

• State

  • JSON
  • rating
  • wins
  • losses
  • match counters

• Key: leaderboard["main"]

• Responsibility: Stores and serves top-ranked players.

• Actions

  • updatePlayer

• Queues

  • None

• State

  • SQLite
  • Leaderboard score rows
  • Top-list ordering

Lifecycle

sequenceDiagram
	participant C as Client
	participant MM as matchmaker
	participant P as player
	participant M as match
	participant LB as leaderboard

	C->>MM: queueForMatch(username)
	MM->>P: initialize/getRating
	P-->>MM: rating
	Note over MM: store queue row + retry pairing
	MM->>M: create(matchId, assigned players)
	MM-->>C: assignmentReady
	C->>M: connect(username)
	M->>MM: matchCompleted(...)
	MM->>P: applyMatchResult(...)
	MM->>LB: updatePlayer(...)
	Note over MM: remove matches + assignments rows

Turn-Based

Actors

• Key: matchmaker["main"]

• Responsibility: Handles private invite and public queue pairing for async matches.

• Actions

  • createGame
  • joinByCode
  • queueForMatch
  • unqueueForMatch
  • closeMatch

• Queues

  • createGame
  • joinByCode
  • queueForMatch
  • unqueueForMatch
  • closeMatch

• State

  • SQLite
  • matches
  • player_pool
  • assignments for invite and queue mapping

• Key: match[matchId]

• Responsibility: Owns board state, turn order, move validation, and final result.

• Actions

  • connect
  • makeMove

• Queues

  • None

• State

  • JSON
  • board
  • turns
  • players
  • connection presence
  • result

Lifecycle

Public Queue

sequenceDiagram
	participant A as Client A
	participant B as Client B
	participant MM as matchmaker
	participant M as match

	A->>MM: queueForMatch()
	B->>MM: queueForMatch()
	Note over MM: pair first two queued players
	MM->>M: create(matchId) + seed X/O players
	MM-->>A: assignment/match info
	MM-->>B: assignment/match info
	A->>M: connect(playerId)
	B->>M: connect(playerId)
	A->>M: makeMove()
	B->>M: makeMove()
	opt all players disconnected for timeout
		Note over M: destroy after idle timeout
	end
	M->>MM: closeMatch(matchId)

Private Invite

sequenceDiagram
	participant A as Client A
	participant B as Client B
	participant MM as matchmaker
	participant M as match

	A->>MM: createGame()
	MM-->>A: {matchId, playerId, inviteCode}
	B->>MM: joinByCode(inviteCode)
	MM->>M: create(matchId) + seed X/O players
	MM-->>A: assignment/match info
	MM-->>B: assignment/match info
	A->>M: connect(playerId)
	B->>M: connect(playerId)
	A->>M: makeMove()
	B->>M: makeMove()
	M->>MM: closeMatch(matchId)

Idle

Actors

• Key: world[playerId]

• Responsibility: Owns one player's progression, buildings, production scheduling, and state updates.

• Actions

  • initialize
  • build
  • collectProduction

• Queues

  • None

• State

  • JSON
  • Per-player buildings
  • resources
  • timers
  • progression state

• Key: leaderboard["main"]

• Responsibility: Stores global scores and serves leaderboard updates.

• Actions

  • updateScore

• Queues

  • updateScore

• State

  • SQLite
  • scores table keyed by player
  • Current leaderboard totals

Lifecycle

sequenceDiagram
	participant C as Client
	participant W as world
	participant LB as leaderboard

	C->>W: getOrCreate(playerId) + initialize()
	Note over W: seed state + schedule collection
	W-->>C: stateUpdate
	loop gameplay loop
		C->>W: build() / collectProduction()
		W->>LB: updateScore(...)
	Note over LB: upsert scores
	LB-->>C: leaderboardUpdate
	W-->>C: stateUpdate
	end

Reference Map

Actors

• Access Control
• Actions
• Actor Keys
• Actor Scheduling
• Actor Statuses
• AI and User-Generated Rivet Actors
• Authentication
• Cloudflare Workers Quickstart
• Communicating Between Actors
• Connections
• Debugging
• Design Patterns
• Destroying Actors
• Ephemeral Variables
• Errors
• External SQL Database
• Fetch and WebSocket Handler
• Helper Types
• Icons & Names
• In-Memory State
• Input Parameters
• Lifecycle
• Limits
• Low-Level HTTP Request Handler
• Low-Level KV Storage
• Low-Level WebSocket Handler
• Metadata
• Next.js Quickstart
• Node.js & Bun Quickstart
• Queues & Run Loops
• React Quickstart
• Realtime
• Scaling & Concurrency
• Sharing and Joining State
• SQLite
• SQLite + Drizzle
• Testing
• Troubleshooting
• Types
• Vanilla HTTP API
• Versions & Upgrades
• Workflows

Clients

• Node.js & Bun
• React
• Swift
• SwiftUI

Connect

• Deploy To Amazon Web Services Lambda
• Deploying to AWS ECS
• Deploying to Cloudflare Workers
• Deploying to Freestyle
• Deploying to Google Cloud Run
• Deploying to Hetzner
• Deploying to Kubernetes
• Deploying to Railway
• Deploying to Vercel
• Deploying to VMs & Bare Metal
• Supabase

Cookbook

• Multiplayer Game

General

• Actor Configuration
• Architecture
• Cross-Origin Resource Sharing
• Documentation for LLMs & AI
• Edge Networking
• Endpoints
• Environment Variables
• HTTP Server
• Logging
• Production Checklist
• Registry Configuration
• Runtime Modes

Self Hosting

• Configuration
• Docker Compose
• Docker Container
• File System
• Installing Rivet Engine
• Kubernetes
• Multi-Region
• PostgreSQL
• Production Checklist
• Railway Deployment
• Render Deployment