SKILL.md

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.

Game Classification

Starter Code

Common Examples

Battle Royale

GitHub

Fortnite, Apex Legends, PUBG, Warzone

Arena

GitHub

Call of Duty TDM/FFA, Halo Slayer, Counter-Strike casual, VALORANT unrated, Overwatch Quick Play, Rocket League

IO Style

GitHub

Agar.io, Slither.io, surviv.io

Open World

GitHub

Minecraft survival servers, Rust-like worlds, MMO zone/chunk worlds

Party

GitHub

Fall Guys private lobbies, custom game rooms, social party sessions

Physics 2D

GitHub

Top-down physics brawlers, 2D arena games, platform fighters

Physics 3D

GitHub

Physics sandbox sessions, 3D arena games, movement playgrounds

Ranked

GitHub

Chess ladders, competitive card games, duel arena ranked queues

Turn-Based

GitHub

Chess correspondence, Words With Friends, async board games

Idle

GitHub

Cookie Clicker, Idle Miner Tycoon, Adventure Capitalist

Server Simulation

Game Loop And Tick Rates

Pattern

Use When

Implementation Guidance

Fixed realtime loop

Battle Royale, Arena, IO Style, Open World, Ranked

Run in run with sleep(tickMs) and exit on c.aborted.

Action-driven updates

Party, Turn-Based

Mutate and broadcast only on actions/events rather than scheduled ticks.

Coarse offline progression

Any mode with idle progression

Use c.schedule.after(...) with coarse windows (for example 5 to 15 minutes) and apply catch-up from elapsed wall clock time.

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.

Dimension

Primary Engine

Fallback Engines

Example Code

@dimforge/rapier2d

planck-js, matter-js

GitHub

@dimforge/rapier3d

cannon-es, ammo.js

GitHub

Spatial Indexing

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

Index Type

Recommendation

AABB index

For AOI, visibility, and non-collider entities, use rbush for dynamic sets or flatbush for static-ish sets.

Point index

For nearest-neighbor or within-radius queries, use d3-quadtree.

Networking & State Sync

Netcode

Model

When To Use

Implementation

Hybrid (client movement, server combat)

Shooters, action sports, ranked duels

Client owns movement and sends capped-rate position updates. Server validates for anti-cheat. Combat (projectiles, hits, damage) is fully server-authoritative.

Server-authoritative with interpolation

IO Style, persistent worlds

Client sends input commands. Server simulates on fixed ticks and publishes authoritative snapshots. Client interpolates between snapshots.

Server-authoritative (basic logic)

Turn-based, event-driven

Server validates and applies discrete actions (turns, phase transitions, votes). Client displays confirmed state.

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

Primitive

Use When

Typical Ownership

matchmaker["main"] + match[matchId]

Session-based multiplayer (battle royale, arena, ranked, party, turn-based)

Matchmaker owns discovery/assignment. Match owns lifecycle and gameplay state.

chunk[worldId,chunkX,chunkY]

Large continuous worlds that need sharding

Each chunk owns local players, chunk state, and local simulation.

world[playerId]

Per-player progression loops (idle/solo world state)

Per-player resources, buildings, timers, and progression.

player[username]

Canonical profile/rating reused across matches

Durable player stats (for example rating and win/loss).

leaderboard["main"]

Shared rankings across many matches/players

Global ordered score rows and top lists.

#### 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

Topic

Summary

Matchmaking

Immediate routing to the fullest non-started lobby (oldest tie-break); players wait in lobby until capacity, then the match starts.

Netcode

Hybrid. Client owns movement, camera, and local prediction. Server owns zone state, projectiles, hit resolution, eliminations, loot, and final placement.

Tick Rate

10 ticks/sec (100ms) with a fixed loop for zone progression and lifecycle checks.

Physics

Client owns movement with server anti-cheat validation; projectiles, hits, and damage are server-authoritative. Use @dimforge/rapier3d for 3D or @dimforge/rapier2d for top-down 2D.

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

Topic

Summary

Matchmaking

Mode-based fixed-capacity queues (duo, squad, ffa) that build only full matches and pre-assign teams (except FFA).

Netcode

Hybrid. Client owns movement plus prediction and smoothing. Server owns team or FFA assignment, projectiles, hit resolution, phase transitions, and scoring.

Tick Rate

20 ticks/sec (50ms) with a tighter loop for live team and FFA snapshots.

Physics

Medium to high intensity; client movement with server validation and server-authoritative combat/entities.

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

Topic

Summary

Matchmaking

Open-lobby routing to the fullest room below capacity; room counts are heartbeated and new lobbies are auto-created when needed.

Netcode

Server-authoritative with interpolation. Client sends input intents and interpolates. Server owns movement, bounds, room membership, and canonical snapshots.

Tick Rate

10 ticks/sec (100ms) with lightweight periodic room snapshots.

Physics

Low to medium intensity; server-authoritative kinematic movement, escalating to a physics engine only when collisions get complex.

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

Topic

Summary

Matchmaking

Client-driven chunk routing from world coordinates, with nearby chunk windows preloaded via adjacent chunk connections.

Netcode

Hybrid for sandbox (client movement with validation) or server-authoritative for MMO-like flows. Server owns chunk routing, persistence, and canonical world state.

Tick Rate

10 ticks/sec per chunk actor (100ms), so load scales with active chunks.

Physics

Medium to high at scale; chunk-local simulation can be server-authoritative (MMO-like) or client movement with server validation (sandbox-like).

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

Topic

Summary

Matchmaking

Host-created private party flow using party codes and explicit joins.

Netcode

Server-authoritative (basic logic). Server owns membership, host permissions, and phase transitions.

Tick Rate

No continuous tick; updates are event-driven (join, start, finish).

Physics

Low intensity for lobby-first flows; usually no dedicated physics or indexing unless you add realtime mini-games.

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

Topic

Summary

Matchmaking

ELO-based queue pairing with a widening search window as wait time increases.

Netcode

Hybrid. Client owns movement with local prediction and interpolation. Server owns projectiles, hit resolution, match results, and rating updates.

Tick Rate

20 ticks/sec (50ms) with fixed live ticks for deterministic pacing and broadcast cadence.

Physics

Medium to high intensity; client movement with server validation and server-authoritative combat/hit resolution.

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

Topic

Summary

Matchmaking

Async private-invite and public-queue pairing in the same pattern.

Netcode

Server-authoritative (basic logic). Client can draft moves before submit. Server owns turn ownership, committed move log, turn order, and completion state.

Tick Rate

No continuous tick; move submission and turn transitions drive updates.

Physics

Very low intensity; no realtime physics loop, just discrete rules validation. Indexing is optional and mostly for board or query convenience at scale.

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

Topic

Summary

Matchmaking

No matchmaker; each player uses a direct per-player actor and a shared leaderboard actor.

Netcode

Server-authoritative (basic logic). Client owns UI and build intent. Server owns resources, production rates, building validation, and leaderboard totals.

Tick Rate

No continuous tick; use c.schedule.after(...) for coarse intervals and compute offline catch-up from elapsed wall time.

Physics

None for standard idle loops; transitions are discrete (build, collect, upgrade) and do not need spatial indexing.

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

multiplayer-game

SKILL.md

Multiplayer Game

Starter Code

Server Simulation

Game Loop And Tick Rates

Physics

Spatial Indexing

Networking &#x26; State Sync

Netcode

Realtime Data Model

Shared Simulation Logic

Interest Management

Backend Infrastructure

Persistence

Matchmaking Patterns

Security And Anti-Cheat

Baseline Checklist

Movement Validation

Architecture Patterns

Battle Royale

Arena

IO Style

Open World

Party

Host Flow

Joiner Flow

Ranked

Turn-Based

Public Queue

Private Invite

Idle

Reference Map

Actors

Agent Os

Clients

Connect

Cookbook

General

Self Hosting

Let your agent run on any real-world website

Related skills

Stop writing automation&scrapers

Networking & State Sync