Version: Unity 6.1 Alpha (6000.1)
Language : English
Web browser compatibility
Web development and publishing process

Technical limitations

Web technology imposes restrictions on Unity web applications designed to run in web browsers. Make sure you’re aware of the following technical limitations before you build your application for the Web platform.

Platform support

Most popular desktop browser versions support Unity Web content, but do note that different browsers offer different levels of support.

The following features in Web builds are either not available or limited due to constraints of the platform itself:

Lack of Web build debug support in Visual Studio

Debugging Web builds isn’t supported in Visual Studio. For more information, refer to Debug and troubleshoot Web builds.

Lack of Unity cache and caching script support

Web builds don’t support the Unity Cache and Caching Scripting API due to restricted access to the filesystem in browsers. Network requests to asset data and AssetBundles are instead cached in the browser cache. Refer to Cache behavior in Web.

Lack of threading support

Threads aren’t supported due to the lack of threading support in JavaScript. This applies to both Unity’s internal use of threads to speed up performance, and to the use of threads in script code and managed dlls. Essentially, anything in the System.Threading namespace isn’t supported.

Networking limitations

There are a few networkingThe Unity system that enables multiplayer gaming across a computer network. More info
See in Glossary
features that Web platform doesn’t support:

  • Browsers don’t allow direct access to IP sockets for networking due to security concerns. For more information, refer to Web networking.

  • .NET networking classes within the System.Net namespace aren’t supported.

  • Web platform doesn’t support native socket access because of security limitations within browsers. Therefore, Web also doesn’t support features like ICMP ping or UnityEngine.Ping.

Graphics limitations

There are some limitations in Web platform with the WebGLA JavaScript API that renders 2D and 3D graphics in a web browser. The Unity Web build option allows Unity to publish content as JavaScript programs which use HTML5 technologies and the WebGL rendering API to run Unity content in a web browser. More info
See in Glossary
graphics API, which is based on the functionality of the OpenGL ES graphics library. For more information, refer to Web graphics.

Audio limitations

Web builds use a custom back end for audio based on the Web Audio API, but it only supports the basic audio functionality. For more information, refer to Audio in Web.

Dynamic generation of code

Web is an AOT platform, so it doesn’t allow dynamic generation of code using System.Reflection.Emit. This is the same on all other IL2CPPA Unity-developed scripting back-end which you can use as an alternative to Mono when building projects for some platforms. More info
See in Glossary
platforms, iOS, and most consoles.

Multithreading support

Although Unity provides multithreading support for native C/C++ code, the Web platform doesn’t yet support C# multithreading due to limitations of WebAssembly. This means that applications built using the Web platform must run on a single C# thread.

Notes:

The recommended way to perform complex asynchronous tasks on the Web platform is to use coroutines. For more information, refer to the coroutines documentation.

The following factors limit the multithreading support:

Constraints on native stack scanning

The Web platform uses WebAssembly, which is a bytecode format for secure and efficient execution of Unity code in web browsers. Web browsers are designed to run the code in a secure and isolated environment which blocks direct access to the native WebAssembly stack. This affects multithreaded garbage collection as the Web garbage collector runs only once at the end of every frame unlike incrementally over multiple frames on other platforms.

No pre-emptive thread signaling support

Background Workers on the web execute code in parallel independently from each other. On native platforms, the main thread can synchronously send signals to the other threads to pause for garbage collection. This synchronous signaling isn’t supported on the web, which prevents WebAssembly compiled C# code from running in multiple threads.

Build and run limitations

Unity uses a web server with only basic functionality to host web builds created with Build and Run (menu: Edit > Build Profiles > Build and Run).

The server doesn’t support data caching, which affects:

  • The .data file, which includes all scenesA Scene contains the environments and menus of your game. Think of each unique Scene file as a unique level. In each Scene, you place your environments, obstacles, and decorations, essentially designing and building your game in pieces. More info
    See in Glossary
    and assets of a build that don’t use AssetBundles or Addressables.
  • Addressables and AssetBundle files.

Additional resources

Web browser compatibility
Web development and publishing process