Playroom Kit and GameRelay are the closest of the multiplayer backends for web games: both are hosted, both need no server code, and in both, one player's browser runs the game as host. The differences are in how you sync state, what's built in, and how you pay.
The short version
| GameRelay | Playroom Kit | |
|---|---|---|
| Server code | None | None |
| Model | A host player plus our server, which relays and checks every message | A host player; shared state synced by the service |
| Syncing state | Entities with owners, smoothed for you; events, requests, claims, inputs | Shared and per-player state (setState, myPlayer().setState), RPCs |
| Engines | Any JavaScript engine (Phaser, Three.js, Kaplay, plain canvas) | JavaScript and React, plus Unity and Godot |
| Built in | Rooms, quick match, room lists, parties, chat, saves, leaderboards, webhooks, host controls | Lobby UI, matchmaking, RPCs, bots, joysticks and gamepads, turn-based mode, stream mode |
| Discord Activities | Not yet | Yes, with dedicated docs |
| For AI agents | llms.txt and two MCP servers (docs, and your account) | llms.txt |
| Pricing | By players online at once and traffic: a free plan (1 game, 16 players online), Basic at $3.99/month | By monthly active users: free for 10 a day, Lite at $10/month with 10,000 MAU |
| Open source | The SDK (MIT) | No |
How you write the game
Playroom gives you shared state: you set keys on the room or on a player, and everyone reads them. It's simple and flexible, and you decide how often to write and how to smooth what you read.
GameRelay asks you to declare what exists (room.define('ship', { x: 'number', y: 'number' })) and who owns each thing. The SDK then decides how often to send, interpolates other players' copies about 100 ms behind, hands the host's objects to a new host when it leaves, and gives late joiners everything. It's more opinionated, and it's built so that code written by an AI model works on a real network on the first try.
Pricing
The models differ. Playroom charges by monthly active users, so a game with many short visits costs more than one with a few regulars. GameRelay charges by players online at the same moment and by traffic, so cost follows how many play together, not how many tried it once. Free tiers: Playroom's covers 10 unique users a day; GameRelay's covers one game with up to 16 players online and 10 GB of traffic a month. See our plans and Playroom's.
Choose Playroom Kit when
- You're building a Discord Activity. Playroom supports it today; GameRelay doesn't yet.
- You work in Unity or Godot, or want Playroom's ready-made lobby UI, bots or phone-as-controller stream mode.
- A small group of regulars plays your game a lot, where per-user pricing comes out cheaper.
Choose GameRelay when
- You want the netcode handled: smoothing, send rates, host handover and late joiners, without tuning.
- An AI assistant writes your code. The guide, starters, MCP servers and model-readable warnings are built for it.
- You need the platform pieces too: parties, chat, saves, leaderboards with anti-cheat rules, and signed webhooks to your own backend.
- Your game gets many short visits, where paying for players online beats paying per user.
Sources
Checked on October 3, 2026 from Playroom's docs and billing page. Products change; if something here is out of date, tell us at support@gamerelay.io and we'll fix it.
Try it
GameRelay has a free plan, no card needed. Get a public key, then follow the quickstart, or point your AI coding agent at llms.txt.