---
title: "Play online together"
description: "For games. Tell your AI agent \"Make it playable online\" (or \"add online multiplayer\")."
url: "/docs/guides/play-online/"
lang: en
index: "/llms.txt"
---
# Play online together

**For games.** Tell your AI agent **"Make it playable online"** (or "add online multiplayer"). It follows the
`multiplayer` Skill that ships with every template (`.claude/skills/multiplayer/` and `.agents/skills/multiplayer/`) and
builds it on KUMODeck's [multiplayer rooms](/docs/guides/multiplayer/index.md). There is no server code to write.

## First, one short question (with prices)

There is no single right way to play online, so the agent asks **once**, in plain words, before it builds anything.
Answer with numbers, or just say "leave it to you":

1. **Who plays?** people you know (send them a 6-letter code to join the same room) / anyone (paired automatically) / both
2. **How fast is the game?** taking turns or mostly talking / relaxed real-time (co-op, party) / fast action
3. **Does cheating, like an impossible score, matter?** no, we play among ourselves / yes, scores that count or prizes
4. **Leave it to you**: the agent picks the cheapest way that fits your game

Each way shows its price first. Per match of 4 players for 30 minutes, paid at cost from your prepaid balance
(the numbers are estimates, not promises):

| Way | Price per match | What you give up |
|---|---|---|
| Send a link or QR code, get a reply link back (people you know) | **0 cents, completely** — nothing goes through KUMODeck | 2 messages instead of 1; on some connections the two devices cannot reach each other and it does not connect (then use the 6-letter code) |
| Tell a 6-letter code once | joining: about 50 cents per million joins (estimate), plus one of the ways below for the game itself | — |
| KUMODeck carries every move | turn-based **about 0.31 cents** (≈ 1,600 matches for $5) · relaxed real-time **about 0.39 cents** (≈ 1,280) · fast action **about 0.47 cents** (≈ 1,060) | nothing is visible to other players; it still cannot judge your game's rules (see below) |
| Players' devices connect directly | moves during the game: **0 cents** · joining the room: **under 0.01 cents** (estimate, not measured yet) | other players can see roughly where you live (city or region) from your connection; nobody stops cheating; at most 8 players |
| Directly, and KUMODeck carries it when needed | the direct price + carrying, billed by the amount sent ($0.05 per GB): turn-based under 0.01 cents, relaxed about 0.2 cents, fast action about 0.3 cents (estimates) | nobody stops cheating; where you live stays hidden when it is carried |
| Directly only, never carried | moves: **0 cents** · joining: under 0.01 cents | two players who cannot reach each other directly simply cannot play together |

What the agent picks from your answers:

| Your answers | Setting the agent writes |
|---|---|
| cheating matters, or more than 8 players | `"transport": "server"` (the default) |
| only people you know, and "leave it to you" | the link or QR invite (no rooms at all; the SDK's link tool), with the 6-letter code as the backup |
| only people you know | `"transport": "p2p"`, `"p2p": { "relay": "fallback" }` — direct first, carried only when direct fails |
| anyone, or both | `"transport": "p2p"`, `"p2p": { "relay": "always" }` — strangers never see where you live |
| leave it to you | the cheapest that fits: `"p2p": { "relay": "fallback" }`, or the server when the game has scores that count or prizes |
| you ask for zero carrying cost | `"p2p": { "relay": "never" }` — some players may fail to connect |

## What the agent does

1. Turns rooms on and adds a mode that fits your answers (for example 2 players for a duel):
   ```sh
   kumodeck features on multiplayer
   kumodeck config push                     # development
   ```
   ```json
   { "multiplayer": { "modes": [{ "key": "duel", "minPlayers": 2, "maxPlayers": 2, "fillTimeoutSeconds": 20 }] } }
   ```
2. Adds a **Play online** button: quick match with anyone, or a private room with a 6-letter code and an invite link
   for the people you choose (`kumo.rooms.quickMatch`, `kumo.rooms.create(mode, { private: true })`, `kumo.rooms.join(code)`).
3. Sends moves with `room.send` and keeps what everyone must agree on (whose turn, the board, scores) in shared state
   (`room.setState`), so a player who reconnects sees the same game.
4. Keeps reconnects working: the SDK reconnects by itself and the server keeps a dropped player's seat for 20 seconds,
   also across a page reload.
5. Deploys to development (`kumodeck deploy --env development`) and tells you how to try it: open the URL in two tabs and
   add `?player=2` to the second one. Production only when you ask.

## What to expect

| | |
|---|---|
| Server-side | who is in which room, room codes, the host, one order of shared state for everyone, size and rate limits, banned players kept out |
| Your game's job | the rules (moves, hits, who won). A modified client can send anything: let the host decide, and check anything worth cheating for (scores that count, rewards) in your own [Functions](/docs/guides/functions/index.md) and database |
| Limits | up to 64 players per room, 30 messages a second per player, 16 KB per message, 64 KB of shared state |
| Good fits | turn-based, board and card games, quizzes, party games, co-op, casual real-time games for small rooms |
| Not a fit | competitive fast-action games that need the server to run the game (FPS, fighting games with rollback, lag compensation) |

Rooms keep nothing after everyone leaves: progress goes in [cloud saves](/docs/guides/saves/index.md), and chat with history
uses [realtime channels](/docs/guides/realtime/index.md) (the `chat` Skill). Usage is billed at cost from your prepaid balance
([Pricing](/docs/pricing/index.md) has a worked example).