Web technology imposes restrictions on Unity web applications which are designed to run in web browsers. Make sure you are aware of the following technical limitations before you build your application for the Web platform.
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:
Debugging Web builds isn’t supported in Visual Studio. For more information, refer to Debug and troubleshoot Web builds.
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.
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.
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 does not support native socket access because of security limitations within browsers. Therefore, Web also doesn’t support features like ICMP ping or UnityEngine.Ping.
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.
Web builds use a custom backend for Audio based on the Web Audio API, but it only supports the basic audio functionality. For more information, refer to Audio in Web.
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.
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 Web platform supports C/C++ multithreading only if you enable Native C/C++ support in the Web Player settingsSettings that let you set various player-specific options for the final game built by Unity. More info
See in Glossary.
The Web platform supports multithreading, when your document is within a secure context.
The following HTTP response headers must be set by the server.
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:
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.
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.