Build your first multiplayer world

A complete walkthrough — join an instance, exchange events, and run one server-authoritative interaction.

This builds a tiny but real multiplayer world: players see each other, can wave, and can press a button that the server validates before rewarding. Uses Instances & Events and the server authority rule.

1. Boot and join

src/client.ts

import { Helix } from '@helix/sdk';

await Helix.init({
  worldId: window.HELIX_WORLD_ID,
  launchTicket: window.HELIX_LAUNCH_TICKET,
});

const instance = await Helix.instance.join();

instance.onPlayerJoined((p) => spawnAvatar(p));
instance.onPlayerLeft((p) => removeAvatar(p));
for (const p of instance.getPlayers()) spawnAvatar(p);

2. A cosmetic event (client-trusted)

Waving doesn't affect value, so the client can drive it.

src/client.ts

Helix.network.on('wave', ({ from }) => playWave(from));

document.querySelector('#wave')!.addEventListener('click', () => {
  Helix.network.send('wave', {});
});

src/server.ts

import { HelixInstance } from '@helix/server-sdk';

export default class MyWorld extends HelixInstance {
  async onEvent(player, event) {
    if (event === 'wave') this.broadcast('wave', { from: player.id });
  }
}

3. A value event (server-authoritative)

A "daily bonus" button grants LIX-adjacent value — so the server decides, enforces the once-per-day rule, and grants. The client only asks.

src/client.ts

const res = await Helix.network.request('claim-bonus', {});
if (res.ok) showToast(`+${res.amount} coins!`);
else showToast(res.reason);

src/server.ts

export default class MyWorld extends HelixInstance {
  async onEvent(player, event) {
    if (event === 'wave') this.broadcast('wave', { from: player.id });
  }

  // request/response handler
  async onRequest(player, event) {
    if (event !== 'claim-bonus') return;

    const key = `bonus:${player.id}:${today()}`;
    const already = await Helix.cloudSave.get<boolean>(key);
    if (already) return { ok: false, reason: 'Already claimed today' };

    await Helix.cloudSave.set(key, true);        // durable, authoritative
    await this.grantCoins(player.id, 50);        // server-side grant
    return { ok: true, amount: 50 };
  }
}

Why this split matters

If the client could grant its own bonus, players would script infinite coins. The wave is harmless client-side; the bonus is decided server-side and recorded in Cloud Save. That's the golden rule in two handlers.

4. Publish

helix validate && helix deploy

Share the link. Open it in two browsers — you'll see two players, waves replicate, and the bonus is claimable once per day per player.

Persist player data

Go deeper on Cloud Save patterns.

Sell an item for LIX

Turn the bonus into a real purchase.

Build your first multiplayer world

1. Boot and join

2. A cosmetic event (client-trusted)

3. A value event (server-authoritative)

4. Publish

Next

Persist player data

Sell an item for LIX

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