Web performance considerations

In general, the Web performance is close to native apps on the GPU, because 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 uses your GPU for hardware-accelerated rendering. The only exception is the slight overhead for translating WebGL API calls and shadersA program that runs on the GPU. More info
See in Glossary to your OS graphics API (typically DirectX on Windows, OpenGL on Mac, and Linux).

On the CPU, Emscripten translates your code into WebAssembly, the performance of which depends on the web browser you’re using. For more information, see the Unity blog post WebAssembly Load Times and Performance.

Be aware of the following considerations:

• Unity provides multithreading for native C/C++ code, but not yet for C# code due to limitations of WebAssembly.
• When using WebGL API for rendering, the CPU side dispatch of WebGL operations is slower than in native OpenGL. As result, for best performance, it is recommended to avoid large numbers of draw calls per frame, so make sure that both instancing and batching techniques are used in your shaders.
• SIMD on the web is supported as part of WebAssembly 2023 feature setA feature set is a collection of related packages that you can use to achieve specific results in the Unity Editor. You can manage feature sets directly in Unity’s Package Manager. More info
  See in Glossary. Make sure to enable WebAssembly 2023 for best performance on newer browsers.

Tip: To see how Unity distributes work to different threads on non-Web platforms, see the new timeline 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
See in Glossary in Unity.

Web-specific settings which affect performance

To improve performance, set Exception support to None in the Player settings for Web by expanding Other Settings > Stack Trace.

Profiling Web

Web supports the Unity profiler. See the Profiler documentation to learn how to set it up.

Web content in background tabs

If Run in background is enabled in the Player settings for the Web platform, or if you enable Application.runInBackground, your content continues to run when the canvas or the browser window loses focus.

However, some browsers can throttle content running in background tabs. If the tab with your content isn’t visible, your content only updates once per second in most browsers. Note that this causes Time.time to progress slower than usual with the default settings, as the default value of Time.maximumDeltaTime is lower than one second.

Throttling Web performance

You might want to run your Web content at a lower frame rate in some situations to reduce CPU usage. For example, on other platforms, you can use the Application.targetFrameRate API to do so.

When you don’t want to throttle performance, set this API to the default value of –1, rather than to a high value. This allows the browser to adjust the frame rate for the smoothest animation in the browser’s render loop, and might produce better results than Unity trying to do its own main loop timing to match a target frame rate.