Net Forge and Summer Engine: two engines built for AI agents, for different games
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.
Pick Summer Engine when you want an agent to build a desktop or mobile game on a Godot-compatible engine, with Summer running the servers, matchmaking and storefront for you. Pick Net Forge when the game lives in a browser tab, you want the source of the whole engine under MIT, and you want an authoritative multiplayer game that already works before the first prompt.
npm create netforge@latest my-game -- --template arena --yesAt a glance
| Summer Engine | Net Forge | |
|---|---|---|
| What it is | "The AI game engine built for people and agents to make games together" (Summer docs) | The open-source multiplayer browser game engine built for AI coding agents |
| Foundation | "A desktop engine compatible with Godot 4" that "follows upstream continuously" (llms.txt) | A TypeScript engine: an ECS and Rapier simulation shared by client and server, a three.js renderer |
| Language | GDScript, with C# for non-web targets (llms.txt) | TypeScript on both sides |
| Where games run | Windows, Mac, Linux, iOS, Android and the web; web builds are for GDScript projects (Summer docs, llms.txt) | Any modern browser, with WebGPU and a WebGL2 fallback |
| Publishing | Summer Games, Steam, itch.io or your own site (Summer docs) | Any static host for the client, your own Node.js server for rooms; see Deploy and host |
| Multiplayer | Summer runs the server for every match, with queues, parties, saves and leaderboards, up to 16 players in a match (Multiplayer) | Authoritative rooms that step the shared simulation; the browser predicts with the same code; ten finished multiplayer games |
| Agent tooling | An MCP server, a summer CLI and specialist agents for Claude Code, Codex, Cursor, Copilot and others (Summer docs) | @netforge/mcp, npx netforge setup agent, Agent Skills and an AGENTS.md in every template; see Agents |
| Source and license | The agent layer (CLI, MCP server, skills) is MIT; the desktop app is free to download but "source code is not public right now" (llms.txt) | Everything in the public repository is MIT |
| Paid parts | "Hosted Summer AI, asset generation, storage, multiplayer, orchestration, and cloud features are paid Summer services" (llms.txt) | The engine, templates, assets and local play are free; the hosted Net Forge service is optional |
| Best for | Native and mobile games made with an agent, with hosting handled for you | Browser games with real multiplayer, where you own the code and the hosting |
When to pick Summer Engine
- You want a native or mobile game. Summer builds for Windows, Mac, Linux, iOS and Android, and publishes to Steam and its own Summer Games store (Summer docs). Net Forge targets the browser only.
- You already have a Godot project. Summer says you can "bring a Godot project and keep building it in Summer" (Summer docs).
- You want hosting, matchmaking, parties and leaderboards run for you. In Summer, "Summer runs the server for every match, so no player has to host", and queues, parties, saves and leaderboards come with the SDK (Multiplayer).
- You want the agent to make art and sound too. Asset generation is one of Summer's hosted services (llms.txt). Net Forge ships a library of 530 CC0 models and sounds by human artists instead; see CC0 game assets.
When to pick Net Forge
- The game is a web page. A Net Forge game is a static client plus a Node.js room server, playable at a link in any modern browser, with no app to install. See Build a multiplayer browser game.
- You want the whole engine's source. The simulation, netcode, renderer, bots and all ten games are MIT in one public repository, so your agent can read every line it builds on.
- You want multiplayer to work before the first prompt. Each template is a finished online game with an authoritative server, client prediction, seat-filling bots and a headless playtest. See Templates and play any of them on itch.io.
- You want the agent kept inside a typed API. Game rules live in one
src/game.tsthat may import only@netforge/engine, so an edit cannot break the netcode. See The typed game API. - You want to own the hosting. The room server runs anywhere Node.js runs. See Host a browser game server.
How the agent workflows differ
Summer gives an agent an engine to operate: the MCP server connects "with one URL and a single sign-in", the CLI runs "any Summer operation from a shell", and specialist agents (researcher, builder, asset maker, verifier, advisor) divide the work (Summer docs). The engine is a desktop application the agent drives.
Net Forge gives an agent code to edit and tools to check it: npx netforge setup agent writes AGENTS.md, CLAUDE.md, Cursor rules and .mcp.json into a project, and the MCP server's tools create a game from a template, explain the API, validate src/game.ts, run the playtest bots and play the game locally. Nothing requires a sign-in, and everything runs on the developer's own computer.
Honest limits of Net Forge
Net Forge is young (0.2.0) and browser only. It has no editor, no native or mobile builds and no asset generation. The public repository's room host is for play on your own computer and network; the production room server with matchmaking and lag compensation is the hosted Net Forge service.
FAQ
Is Summer Engine open source?
Partly. Summer's agent layer (the CLI, MCP server, skills, hooks and plugin manifests) is MIT, while the desktop app is free to download but its source is not public at the time of writing (llms.txt). Net Forge's public repository is MIT throughout.
Can a Summer Engine game run in the browser?
Summer exports web builds for GDScript projects, and its docs say web builds play in the browser on Summer Games (llms.txt). Check Summer's current docs for which multiplayer features web builds support.
Does Net Forge publish to Steam or app stores?
No. Net Forge games are browser games. Publish the client to any static host and run the room server on Node.js.
Which one works with Claude Code or Cursor?
Both. Summer lists Claude Code, Codex, Cursor, Copilot and others as supported agents (Summer docs). Net Forge works through its MCP server and the files npx netforge setup agent writes; see Build a game with an AI agent.
Can I use both?
They do not share a runtime: Summer games are Godot-compatible projects and Net Forge games are TypeScript. Pick by where the game will run.