sbox is Facepunch's modern game engine built on Valve Source 2 and .NET, with games coded in C# and an editor for visual iteration. The engine and editor run locally from the game folder after a Steam install or a from-source setup, and documentation with API references is published at sbox.game/dev. Engine source is MIT-licensed while native binaries in game/bin fall under the sbox EULA.[1][2][3][4]
Quick verdict
sbox is a free, MIT-licensed game engine on Valve Source 2 with C# authoring and millisecond hotload, aimed at teams prototyping multiplayer and small-to-medium 3D games. The editor installs from Steam and the source builds on Windows, Linux, and Apple Silicon Macs, while standalone export stays in preview with Valve approval and PC-only limits.[1][2][3][4]
Key features
C# authoring with millisecond hotload C# authoring with millisecond hotload: code changes compile within milliseconds so iteration stays in the editor loop rather than restarting builds.[1][2]
Source 2 rendering, physics, and audio Source 2 rendering, physics, and audio: the engine builds on Valve Source 2 systems for rendering, resources, physics, and audio, with the native core shipped as prebuilt binaries.[1][2]
Unity-like scene system Unity-like scene system: the official docs describe a scene system similar to Godot and Unity so iteration is visual instead of everything being code-based.[1]
Steam editor install or source build Steam editor install or source build: the editor installs directly from Steam, and Setup.bat or Setup.sh builds from source with Git, the .NET 10 SDK, and an IDE.[1]
Standalone export in preview, no royalties Standalone export in preview, no royalties: standalone executable export is in preview, takes no Facepunch engine royalties or revenue share, but needs individual Valve approval plus a Facepunch standalone license and is PC only with no console or mobile exports.[1]
MIT engine source with scoped binaries MIT engine source with scoped binaries: the 2025 Facepunch Studios MIT grant covers the engine source with third-party components separately licensed, while native binaries in game/bin fall under the sbox EULA, not MIT.[1][2]
Windows, Linux, and Apple Silicon Macs Windows, Linux, and Apple Silicon Macs: supported setups are Windows 10/11 x64, Linux x64 via the Steam Linux Runtime, and macOS Apple Silicon, with Intel Macs stated unsupported.[1]
Docs, tutorials, and API references Docs, tutorials, and API references: full documentation, tutorials, and API references are published at sbox.game/dev, and issues are tracked in the sbox-public repository.[1][2]
Who will love it
Teams doing rapid game prototyping with live code hotload: millisecond recompiles and a visual scene system suit iteration speed over pipeline ceremony.[1][2]
Teams running multiplayer game experiments on a shared platform: engine and editor run locally from the game folder with Steam distribution for sharing builds.[1]
Teams building small-to-medium 3D games on Source 2: documented rendering, physics, and audio systems cover the core needs of that scope without a proprietary engine seat.[1][2]
Who should avoid it
Teams without toolchain appetite: the Steam editor path is easy but building from source needs Git, the .NET 10 SDK, platform setup scripts, and an IDE, so overall setup is moderate.[1]
Teams needing shippable standalone builds now: standalone export is in preview, requires individual Valve approval and a Facepunch license, and excludes console and mobile targets.[1]
Teams needing confirmed enterprise controls: enterprise support or SLAs, SSO, data-location lists, offline independence, and team-size guidance were not evidenced in this pass, so regulated adopters must verify these before committing.[1][2]
Alternatives and compatibility
The evidenced engine-selection overlap is Godot: both are open game engines for building games and sbox docs explicitly compare its scene system to Godot and Unity. Scope is new-game engine selection; no migration guide or vendor endorsement is claimed.[1][2]
License-sensitive adopters should note the boundary precisely: engine source is MIT per LICENSE.md while game/bin native binaries fall under the sbox EULA, with third-party components separately licensed.[1][2]
sbox fits teams that can carry a Steam plus .NET toolchain setup on Windows, Linux, or Apple Silicon Macs and want C# hotload iteration on Source 2 with no engine royalties.[1][2][3]
Questions worth asking
What is sbox best for?
How much does sbox cost per month?
As checked October 12, 2026, the engine source is MIT-licensed and Facepunch takes no engine royalties or revenue share, so there is no engine license fee; standalone export additionally needs a Facepunch standalone license with individual Valve approval. Confirm current standalone terms on sbox.game before budgeting.[1][2]
Can you self-host sbox?
Yes, in the self-run sense: the engine and editor run locally from the game folder on the user's own machine after a Steam install or a from-source setup on Windows, Linux, or Apple Silicon Macs. Intel Macs are stated unsupported, and no hosted or managed-cloud edition was evidenced.[1]
Sources and editorial review
Source research. Reviewed on October 12, 2026. Written by Sanjib Sah. AI assisted; reviewed by a human editor.
We have not run or tested this product.
- Facepunch/sbox-public repository
official · Observed October 12, 2026
GitHub repo page for Facepunch/sbox-public: describes a modern game engine on Valve Source 2 and .NET with an editor; shows 2,378 commits and a LICENSE.md file.
- sbox-public README
official · Observed October 12, 2026
README: C# engine/editor/tooling plus game content; native Source 2 core as prebuilt binaries; Steam install; Setup.bat/Setup.sh for Windows, Linux, macOS Apple Silicon; needs Git, .NET 10 SDK, and an IDE; game and editor run from the game folder; docs and API references at sbox.game/dev; engine source under MIT.
- sbox-public LICENSE.md
official · Observed October 12, 2026
LICENSE.md: 2025 Facepunch Studios Ltd MIT grant for the software; third-party components separately licensed; README adds that game/bin native binaries fall under the sbox EULA, not MIT.
- S&box Documentation
official · Observed October 12, 2026
Official docs: sbox coded in C# on Source 2 systems (rendering, resources, physics, audio); hotload compiles changes within milliseconds; scene system similar to Godot and Unity; issues tracked in the sbox-public repo.
- Exporting Standalone - S&box docs
official · Observed October 12, 2026
Exporting Standalone doc: standalone executable export is in preview, needs individual Valve approval and a Facepunch standalone license; no Facepunch engine royalties or revenue share; PC only with no console or mobile exports.
- sbox on OpenAlternative directory
community · Observed October 12, 2026
Directory lead only: lists sbox as a game creation platform on Source 2, alternative to Unreal Engine and Unity, linking sbox.game and the facepunch/sbox-public repo with MIT license and recent commit activity.
Compared with these products
No explicit proprietary baseline is recorded.