Version: 2020.3
Language : English
WebGL: Server configuration code samples

Debug and troubleshoot WebGL builds

Visual Studio doesn’t support debugging Unity WebGLA JavaScript API that renders 2D and 3D graphics in a web browser. The Unity WebGL 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
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content. Use the following tips to get your build information.

The browser’s JavaScript console

Unity WebGL doesn’t have access to your file system, so it doesn’t write a log file like other platforms. However, it does write all logging information such as Debug.Log, Console.WriteLine or Unity’s internal logging to the browser’s JavaScript console.

To open the JavaScript console:

  • In Firefox, press Ctrl-Shift-K on Windows or Command-Option-K on a Mac.
  • In Chrome, press Ctrl-Shift-J on Windows or Command-Option-J on a Mac.
  • In Safari, go to Preferences > Advanced > Develop, and press Command-Option-C.
  • In Microsoft Edge or Internet Explorer, press F12.

Development builds

For debugging purposes, you might want to make a development build in Unity (open the Build Settings window and enabled the Development BuildA development build includes debug symbols and enables the Profiler. More info
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checkbox). Development builds allow you to connect the profilerA window that helps you to optimize your game. It shows how much time is spent in the various areas of your game. For example, it can report the percentage of time spent rendering, animating, or in your game logic. More info
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, and Unity doesn’t minify them, so the emitted JavaScript code still contains human-readable (though C++-mangled) function names. The browser uses these to display stack traces if you run into a browser error, when using Debug.LogError, or when an exception occurs and exception support is disabled. Unlike the managed stack traces that can occur when you have full exception support (see below), these stack traces have mangled names, and contain not only managed code, but also the internal UnityEngine code.

Exception support

WebGL has different levels of exception support (see documentation on Building for WebGL). By default, Unity WebGL only supports explicitly thrown exceptions. You can enable Full exception support, which emits additional checks in the IL2CPP-generated code, to catch access to null references and out-of-bounds array elements in your managed code. These additional checks significantly impact performance and increase code size and load times, so you should only use it for debugging.

Full exception support also emits function names to generate stack traces for your managed code. For this reason, stack traces appear in the console for uncaught exceptions and for Debug.Log statements. Use System.Environment.Stacktrace to get a stack trace string.


Problem: The build runs out of memory

This is a common problem, especially on 32-bit browsers. For more information on WebGL memory issues and how to fix them, see documentation on Memory in WebGL.

Problem: Files saved to Application.persistentDataPath don’t persist

Unity WebGL stores all files that must persist between sessions (such as PlayerPrefs or files saved in persistentDataPath) to the browser IndexedDB. This is an asynchronous API, so you don’t know when it’s going to complete.

Call the following code to make sure Unity flushes all pending file system write operations to the IndexedDB file system from memory:

FS.syncfs(false, function (err) {
  if (err) {
    console.log("Error: syncfs failed!"); 

Error message: Incorrect header check

The browser console log usually prints this error due to incorrect server configuration. For more information on how to deploy a release build, see documentation on Deploying compressed builds.

Error message: Decompressing this format (1) isn’t supported on this platform

The browser console log prints this error when the content tries to load an AssetBundle compressed using LZMA, which Unity WebGL doesn’t support. Re-compress the AssetBundle using LZ4 compressionA method of storing data that reduces the amount of storage space it requires. See Texture Compression, Animation Compression, Audio Compression, Build Compression.
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to solve this problem. For more information on compression for WebGL, see documentation on WebGL building, particularly the AssetBundles section.

  • MonoDevelop replaced with Visual Studio from 2018.1
WebGL: Server configuration code samples
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