s&box
S&box (stylized as s&box, pronounced Sandbox) is a platform and game development toolkit developed by Facepunch studio powered by a highly modified version of Source 2. Initially, the development was based on Unreal Engine 4, but as soon as Half-Life: Alyx came out, Facepunch immediately requested the engine branch of the newly-published game. A few weeks later Valve gave Facepunch access to the terabyte large repository, after which, in 2020, s&box's transition to Source 2 was announced. This is the first (and currently only) time that Source 2 has been licensed to third-party developers. s&box comes with a complete development package including a modified and fully featured Source 2-derived engine toolkit with C# bindings, and a distribution platform named sbox.game
While s&box offers a sandbox mode (called Sandbox, under "Games"), which acts as a spiritual successor to Garry's Mod, s&box shares more similarity to game platforms like Roblox. Users can create and publish their games to s&box or even directly to Steam, completely royalty-free.[1][2] s&box was released on April 28, 2026. s&box's public source code can be found here.
Features
Added
s&box runs on highly modified version of Source 2 with the following features:
- AMD FSR upscaler (1.0 and 3.0) and FSR Native AA
- An open-source upscaling algorithm developed by AMD, which does not rely on machine learning and runs on traditional shading units, allowing it to work on any GPU vendor. FSR version 3.0 are temporal-based compared to 1.0. When the user chose to run the game on lower resolutions to improve performance, FSR will attempt to upscale and sharpening the image to make it less blurry on native monitor resolution. Additionally, FSR 3.0 also came with FSR Native AA, a temporal-based anti-aliasing solution designed for native resolution.
- C# scripting
- Todo: Description
- Box3D physics
- A new physics engine that can be quickly updated, closely related to Rubikon, and will eventually be free and open source. During development of s&box, Rubikon was switched to Izabu, which is a cleaned-up and modified version of Rubikon without Valve-specific code, then later being replaced again by Box3D.
- Hotloading
- The ability to see code changes take effect immediately with blazing fast hotloading, no need to compile and restart your game.
- Mounting assets from games on different engines
- In S&Box, you can mount any assets from games built on different engines. Currently as of August 2025 Update and at launch in April 2026, S&Box can mount Quake, GoldSrc, Natural Selection 2, and others and can spawn models or props from these games & engines.
- Scenes System
- s&box does away with the legacy Entity System (from Quake engine) and utilizes a Scene System which lets you have a Scene that is a collection of Game Objects to make up the game world. It closely resembling the way things are done in Unity engine.
- Visual Scripting
- With ActionGraph and Doo you can create interactive experiences in your levels, without having to write a single line of code, or having sprawling chains of entities. Not meant to program a game entirely in it, but to augment it.
Changed / removed
Features that were changed or removed in s&box version of Source 2.
- Removed DirectX 11® (Direct3D 11) support
- Support for Direct3D 11 has been removed. Vulkan (1.2 or later) is required to run the game.
UGC Content Distribution
Instead of using the Steam Workshop for storing UGC Content s&box uses a custom web based backend called Workshop.
Maps
Mappers are provided with a modified version of the Source 2 Hammer map editor, with some parts exposed for C# scripting for increased flexibility. This includes integration with the scene system which lets you place game objects with components within the map just like you would in the scene editor.
Project control panel
In the projects menu in the dev tools, you can restrict map selection for your game mode. You can limit it to specific curated maps or maps tagged with supporting the game mode.
Publication
Currently, maps can be included with a game mode or released as a separate project(one for each map). The map is published by clicking on a special button in the projects menu in the developer toolkit.
Characteristics
| Available territory | Unlimited for models, but 32768 units (624.23 m / 2048 ft) for meshes |
| Visibility | Unlimited. The player currently sees approximately 78740 units (2 km / 6561,68 ft) in front of him by default, but values can be increased using C# |
Note: Hammer will be removed in the future. Unknown when exactly but its likely to be removed when scene mesh editing is good enough to replace it.
Warning: Lighting baking beyond 32768 units is temporarily unavailable. Warning: The nav mesh has not yet been adapted for large spaces, which will cause your OS to freeze or ran out of memory if the size of the available territory exceeds 32768 units. In the event of a freeze, the only way out will be an emergency shutdown of the computer. Turn off the navigation mesh in the map compilation window! Warning: There are problems with Floating point precision. Polygons start behaving incorrectly if you are too far from the zero coordinates (faint defects start after crossing 8 km, and are extremely noticeable after 20 km) Programming
s&box user content is programmed with C#, Microsoft's managed, object-oriented programming language of .NET fame. s&box includes an API which provides bindings to the underlying Source 2 engine and to Facepunch's middleware. All code in user content is distributed in source form, which s&box later compiles on-demand with Roslyn. Language support is stated to permit C# 14, indicating that S&box requires a .NET 10 runtime in order to function, which is bundled with the s&box installation. Only a specific subset of the baseline .NET Core complement is available for use.
Security is a primary concern with user content. C# and its ubiquitous pairing with .NET is a software ecosystem many magnitudes larger, more complex, and more powerful than s&box or Source 2. Awarding unchecked access to this leviathan would effectively turn user content into fully-fledged applications with potentially unlimited access to the host computer. To this end, s&box restricts the use of certain types and namespaces. For example, access to the local file system is only available through a sanctioned abstraction layer; System.IO.File and similar types may not be used. This practice is common among applications which attempt to distill down .NET into a limited "scripting" platform for untrusted user code.
Currently, the C# API and tools are in a preview stage of development. Breaking changes happen often and the API is not yet complete.
- Confirm exact subset of available .NET Core components.
There are many similarities between the use of C# in s&box and the use of the more primitive Lua language in 
Garry's Mod. Many concepts of GMod's Lua environment have been carried over, including limited access to the language's features and "hot reloading" of edited code.
s&box will also have a visual scripting solution called ActionGraph, which enables a developer to script events via nodes.
Shaders
You can create your own shaders either through HLSL or through the provided Shadergraph Editor and customize their interface for the material editor.
s&box supports HLSL 2021 & Shader Model 3.0 up to 5.0.
Reception
When S&box first launched, it received mixed reviews. Most players complained about the user generated content (UGC) like games containing low-quality AI-generated content (assets or thumbnail), performance issues and more.
Standalone games powered by s&box
References
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External links
- For Developers
- Report a bug
- Documentation
- API Reference
- Wiki[dead link][confirm]
- Source code (minus C++ code)
- Other