How to make an .io game

The .io architecture

• Positions — direct channel, 15–20 times per second, interpolated on mp.now().
• Pellets — claimed with setnx: first claim wins, the second gets a refusal.
• Score — shared state with a monotonic rule and a delta_max, so it can only go up, a little at a time.
• Leaderboard — mp.submitScore('arena', score, { periods: ['all','daily'] }) at death.

const room = await mp.quickmatch({ mode: 'io', max_players: 64 });

room.on('peer', (p, from) => snakes.update(from, p));
setInterval(() => room.send(me.head()), 60);

function tryEat(pellet) {
  room.setnx(`pellets.${pellet.id}`, mp.account.id);
  room.inc(`players.${mp.account.id}.score`, 1);
}
room.on('rejected', () => { /* somebody got there first: that pellet is gone */ });

async function die(score) {
  await mp.submitScore('arena', score, { periods: ['all', 'daily'] });
  const top = await mp.leaderboard('arena', { period: 'daily', limit: 10 });
}

Rooms hold up to 128 players and a game can run 2,000 live rooms, so quickmatch simply opens a new arena when one fills. Our slither demo and arena demo implement this and their source is readable in the browser.