# SteonMod > SteonMod (the app is called Fusion) fuses games a player owns: each game is connected by a router (data in router.toml plus a little sandboxed Lua) that splits it into blocks players wire together with no code. Routers are free. Start with the agent pack, then the page for your game's engine. ## About - [What is SteonMod?](https://steonmod.com/docs/introduction.md): SteonMod lets you fuse the games you own : play Minecraft's character in another game's world, drop one game's creatures into a playground, or build a whole new game out of pieces… - [Staying safe](https://steonmod.com/docs/safety.md): Fusion runs other programs and changes games, so it's worth knowing exactly what it does. What Fusion does to your games It starts them for you , the way their router says (usuall… - [Fixing problems and FAQ](https://steonmod.com/docs/troubleshooting.md): Fusion tries to say what went wrong in plain words. Here are the common ones and what to do. Fusion doesn't start "Windows protected your PC" when installing: the installer isn't… ## Getting started - [Installing Fusion](https://steonmod.com/docs/installing.md): What you need Windows 10 or 11, 64 bit. A graphics card with DirectX 12 (most from 2016 on). Fusion and your games share it. Enough memory for two games at once. 16 GB of RAM work… - [Your first fusion](https://steonmod.com/docs/first-fusion.md): This page walks you from the Library to playing, in about five minutes. Finding your way Fusion looks like a game store's library. Along the top are four tabs: LIBRARY (Fusion ope… - [My Games](https://steonmod.com/docs/my-games.md): My Games lists every game Fusion found on your PC and what it can do with each. Steam games are found from your Steam libraries; other games are found by their router. What each s… - [Building with cards](https://steonmod.com/docs/building-with-cards.md): Build a scenario (in Create ) makes a scenario without writing any file. It has three parts: Left: cards. Every block from every router you have, grouped by game. Cards of games t… - [The sandbox](https://steonmod.com/docs/sandbox.md): Every plain scenario is a sandbox, like Garry's Mod: spawn things from any game in it, carry them around, weld them, change them. (Experiences decide what you may do, so some of t… - [Devices](https://steonmod.com/docs/devices.md): Devices are Fusion's no code building pieces. Put one in the world, change its settings, and it does its job: show a message, count down, react when you walk somewhere, drop props… - [Getting content](https://steonmod.com/docs/content.md): Content (the tab at the top) is where routers, scenarios, Experiences, addons and Devices come in. They come from two places: The content hub : steonmod.com's list of signed packa… ## Making routers - [Start here](https://steonmod.com/docs/making-routers.md): For people who connect a game to Fusion, and for the AI agents they work with. Read this page first; it says which other page you need. A router connects one game to Fusion. It sp… - [Porting your passthrough mod](https://steonmod.com/docs/porting.md): For authors of passthrough mods (a SkyCraft port, "Minecraft in ", a ReShade bridge) who want their game in Fusion. Start with making routers.md if you haven't. The fast way: fusi… - [The Router API](https://steonmod.com/docs/router-api.md): A router splits one game into blocks (see block manifest.md ). The Router API is how a router tells the game's kit where those blocks are inside the game: which character is the p… - [Router manifests and scenarios](https://steonmod.com/docs/block-manifest.md): Two small TOML files describe everything Fusion needs to fuse games: File Written by Says router.toml (one per game) router makers which blocks a game offers, what each one needs… - [Guest SDK](https://steonmod.com/docs/guest-sdk.md): For programs whose source you have (open source games, Rust rewrites, recomps, your own game), and for your own plugin inside a closed game (a BepInEx or MelonLoader plugin, an SK… - [The agent pack (for AI agents)](https://steonmod.com/docs/agent-pack.md): name: fusion router description: Make, fix or extend a Fusion router (routers/ /router.toml, router.lua, or a game plugin on Fusion's guest SDK) for any game, or bring a passthrou… - [Unreal routers (Fusion's Unreal kit)](https://steonmod.com/docs/agent-unreal.md): The Unreal kit is a UE4SS mod (a Rust DLL, a little C++, Lua) that Fusion's one click setup puts in the game. It works on Unreal 4.12 to 5.x, Direct3D 11 and 12. From Unreal's con… - [Unity routers (Fusion's Unity kit)](https://steonmod.com/docs/agent-unity.md): For Unity games built with IL2CPP (a GameAssembly.dll next to the game's exe). The kit is a MelonLoader mod plus fusion unity.dll . Unity Mono games (a Data/Managed folder, BepInE… - [Routers on the guest SDK: your plugin or program speaks Fusion](https://steonmod.com/docs/agent-sdk.md): For games no kit covers (Unity Mono, Bethesda, Source, custom engines) through your own plugin in the game's mod loader (BepInEx, MelonLoader, OWML, SKSE/F4SE/NVSE, a Source serve… - [Cheaper AI agents](https://steonmod.com/docs/agent-efficiency.md): Written 2026 10 03 from research done that day (sources at the end). The user's goal: making a fusion in Fusion should cost a developer's AI agent far fewer tokens than today's ha… - [Packages and publishing](https://steonmod.com/docs/publishing.md): BUILD.md step 4.6. Code: crates/fusion core/src/content.rs (format, sources, resolution, install), crates/fusion godot/src/content.rs ( FusionContent ), godot/scripts/content brow… - [Signatures and trust](https://steonmod.com/docs/trust.md): BUILD.md steps 6.1 6.3, VISION.md §9 ("Trust & safety") and §11 (takedown rules). Code: crates/fusion core/src/trust.rs , publish.rs , content.rs ; commands in fusion cli keys , p… ## Kits - [Unreal kit](https://steonmod.com/docs/kit-unreal.md): Makes an Unreal Engine game a Fusion guest. Built in BUILD.md step 1.4 with VEIN Demo (Unreal 5.6, D3D12) as the first game. It shows the game's world inside Fusion, drawn from Fu… - [Unity kit](https://steonmod.com/docs/kit-unity.md): Makes a Unity game a Fusion guest. Built in BUILD.md step 7.1 with The Long Dark (Unity 6, IL2CPP, Direct3D 11) as the first game. It shows the game's world inside Fusion, drawn b… - [Minecraft (Fabric) kit](https://steonmod.com/docs/kit-fabric.md): Our fork of SkyCraft's Fabric mod (MIT, see THIRD PARTY NOTICES.md at the repo root). It started as an exact copy of third party/skycraft/fabric (commit bfcaf17 ) in BUILD.md step… - [SkyCraft notes (for the Fabric kit)](https://steonmod.com/docs/skycraft-notes.md): How SkyCraft 0.1.2 actually works, read from its code ( third party/skycraft , commit bfcaf17 ) on 2026 10 03, and what that means for Fusion. Its docs/DESIGN.md is a v0.1 draft a… - [Bevy plugin](https://steonmod.com/docs/sdk-bevy.md): A game made with Bevy (0.19) joins Fusion as a guest by adding one plugin and marking things with components. Its own systems keep running every mechanic; the plugin only shows Fu… ## Scripting - [Lua API](https://steonmod.com/docs/lua-api.md): Addons are small Lua programs that add things to Fusion: tools, props, game modes, rules. Fusion uses Luau (the Lua used by Roblox), so anything you know from Lua or Garry's Mod m… ## Reference - [Fusion protocol](https://steonmod.com/docs/protocol.md): How Fusion and a guest game talk. The exact byte layout is defined in schema/fusion.fidl ; this page explains the ideas. The pieces Piece What it is Who writes Discovery mapping L… - [Schemas and type files](https://steonmod.com/docs/files.md): Files for editors and AI agents. Point your editor's TOML or JSON support at the schemas, and your Lua language server at the type files, and you get completion and errors as you… - [Design decisions](https://steonmod.com/docs/decisions.md): Short records of choices that shaped Fusion, with what was considered and why. Each one is kept as written; a later decision that changes one says so. Decision 0001 Composite gues… - [0001: Composite guest frames by GPU-copying them into Godot-owned textures](https://steonmod.com/docs/adr-0001.md): Date: 2026 10 02 Status: accepted (step 0.9) Context Guests render into shared D3D12 textures (color + linear depth). Fusion (Godot 4.7.2, D3D12) has to draw them inside its scene… - [0002: One Luau VM per addon, with a time limit instead of an instruction count](https://steonmod.com/docs/adr-0002.md): Date: 2026 10 02 Status: accepted (step 0.11) Context BUILD.md §3.9 asks for a Luau sandbox with a per script memory limit and an interrupt callback that stops runaway loops, with… - [0003: The Unreal kit draws with SceneCaptures and copies them on the game's own GPU queue](https://steonmod.com/docs/adr-0003.md): Date: 2026 10 03 Status: accepted (step 1.4) Context BUILD.md step 1.4 asks for VEIN Demo (Unreal 5.6, D3D12) as a Fusion guest: Fusion's camera drives the game's view, and the pi… - [0004: The Router API: data first, Lua 5.4 for router scripts](https://steonmod.com/docs/adr-0004.md): Date: 2026 10 04 Context Every kit needs the same way to say "this is the game's player, these are its NPCs, this is how to get into its world". Before 5.2, VEIN's router was a 22… - [0005: The content hub is a signed static folder of our own](https://steonmod.com/docs/adr-0005.md): Date: 2026 10 04 Context Before Steam, Fusion needs a place where players find routers, scenarios and addons (VISION.md §7.6) that doesn't depend on Steam (§2 rule 1). BUILD.md 6.… ## Contributing - [Releasing Fusion](https://steonmod.com/docs/releasing.md): BUILD.md steps 6.4 6.6. Code: tools/fusion cli/src/release.rs (making a release), tools/fusion launcher ( Fusion.exe : installer, launcher, updater), crates/fusion core/src/releas… ## Files - [router.schema.json](https://steonmod.com/docs/files/router.schema.json) - [scenario.schema.json](https://steonmod.com/docs/files/scenario.schema.json) - [package.schema.json](https://steonmod.com/docs/files/package.schema.json) - [router-api.lua](https://steonmod.com/docs/files/router-api.lua) - [fusion-addons.d.luau](https://steonmod.com/docs/files/fusion-addons.d.luau) - [example-unreal.router.toml](https://steonmod.com/docs/files/example-unreal.router.toml) - [example-unreal.router.lua](https://steonmod.com/docs/files/example-unreal.router.lua) - [example-unity.router.toml](https://steonmod.com/docs/files/example-unity.router.toml) - [example-sdk.router.toml](https://steonmod.com/docs/files/example-sdk.router.toml)