Implement Multiplayer Workflow

Overview

This skill guides you through enabling and integrating multiplayer functionality for games on the Remix platform. Current platform support is two-player, turn-based multiplayer using the SDK multiplayer namespace.

Prerequisites

• A game must be created on the Remix platform (you need a game ID).
• The REMIX_API_KEY environment variable must be set.
• The game must include the RemixSDK script tag:

  <script src="https://cdn.jsdelivr.net/npm/@remix-gg/sdk@latest/dist/index.min.js"></script>
  

Steps

1. Check for Existing Game ID

Use gameId from task context or prior tool results when available.

Otherwise, read the nearest .remix-cli.json. Older projects may still use .remix-mcp.json. If either contains a gameId, reuse it.

Only if none of those sources contain a gameId should you follow the upload-game workflow to create one.

2. Enable Multiplayer

Do not rely on updateGame or a direct REST isMultiplayer toggle. Upstream workflow docs currently treat multiplayer platform enablement as a Remix-side flag, not a public agent mutation.

3. Integrate Multiplayer in Game Code

const sdk = window.RemixSDK
await sdk.ready()

// Access all players in the session
const players = sdk.players // Array of player objects

// Listen for game state updates from other players
sdk.onGameStateUpdated((state) => {
  // Sync game state from other players
})

// Send game state to the other player when a turn ends
sdk.multiplayer.actions.saveGameState({
  gameState: currentState,
  alertUserIds: [opponent.id],
})

Important: Use Multiplayer gameOver

For multiplayer games, use multiplayer.actions.gameOver -- NOT singlePlayer.actions.gameOver. Pass a score array with player IDs:

sdk.multiplayer.actions.gameOver({
  scores: [
    { playerId: player.id, score: playerScore },
    { playerId: opponent.id, score: opponentScore },
  ]
})

Keep Standard Hooks

Multiplayer games still need these callbacks:

sdk.onPlayAgain(() => {
  // Reset game state and restart
})

sdk.onToggleMute(({ isMuted }) => {
  // Mute or unmute all audio
})

Tips

• Use sdk.players to get the two players and their IDs; multiplayer is currently two-player only.
• onGameStateUpdated fires whenever another player sends state -- validate it before applying it, and use sdk.multiplayer.actions.refuteGameState(...) when an incoming update is invalid.
• Use alertUserIds when saving multiplayer state so the next player is notified that it is their turn.
• Do NOT mix singlePlayer.actions.gameOver and multiplayer.actions.gameOver in the same game. Use one or the other.