How to vibe-code a multiplayer game you can actually ship
Net Forge, the open-source multiplayer browser game engine built for AI coding agents, is published on npm under @netforge with source at github.com/netnetdev/net-forge.
Start from a finished multiplayer game instead of a blank page, let your agent change only the rules file, and gate every change on a bot playtest. With Net Forge that is three commands, and the parts that usually sink a prompted multiplayer game (netcode, server authority, rendering, bots) are already done before your first prompt.
npm create netforge@latest my-game -- --template party --yes
cd my-game
npm run play -- --players 2Where prompted multiplayer games usually break
| Problem | What Net Forge does instead |
|---|---|
| The agent writes networking from scratch and it desyncs. | The template's netcode runs the same simulation on the server and the client. The agent never writes it. |
| Clients decide outcomes, so anyone can cheat. | The server decides every hit, kill and pickup. Game code is declarations the server runs. |
| Each prompt touches many files and something unrelated breaks. | The game is one file, src/game.ts, and it may import only @netforge/engine. |
| Nobody can tell if a change made the game worse. | npm run check plays the game with bots and reports kills, progress, softlocks and design metrics as JSON. |
| It works on one machine and nowhere else. | The same game folder plays locally with npm run play and can be published through the hosted studio. |
1. Pick the closest template
Choose the template nearest to the game you imagine and change it, rather than describing a new game from nothing. npm create netforge@latest -- --list prints all ten. See Templates.
2. Give the agent one rule
Put this in your first prompt, or rely on AGENTS.md, which already says it: "Only edit src/game.ts. After every change, run npm run check and fix what it reports before you stop."
3. Prompt in small, playable steps
One idea per prompt keeps each change testable: a new enemy, then a boss, then a store item. Play between prompts with npm run play.
4. Ship it
When it plays well locally, publish it through the hosted Net Forge studio, or keep it as an open-source project that anyone can run with npm run play. See Deploy and host your game.
Alternatives
- Rosebud is a hosted, browser-based builder for prompting games into existence, a good fit when you want everything in one web app.
- Phaser with its official agent tooling is a strong choice for 2D games where you want full control of the code.
- Your own engine gives you every choice and every bug. Net Forge suits you when you want the multiplayer foundation finished and owned by you under MIT.
FAQ
Can you vibe-code a multiplayer game?
Yes, if the multiplayer foundation exists before the first prompt. Starting from a Net Forge template, the agent changes the game rules in one file while the template supplies the server authority, netcode and rendering.
Which template is best for a first vibe-coded game?
The survivor-like (survivor) and the party game (party) respond most visibly to small prompts: enemies, weapons, rounds and pacing are all one-line declarations.
How do I stop the agent from breaking things?
Keep it in src/game.ts and make npm run check part of every change. The play build already rejects imports other than @netforge/engine.
Does vibe-coding with Net Forge cost money?
The engine, templates and tools are free and MIT licensed. Your coding agent's own pricing is separate.