Understanding %temp%\.net Folder | WPF | Single File | Self Contained | WebView2

Question

Understanding %temp%\.net Folder | WPF | Single File | Self Contained | WebView2

Theiss, Daniel 0

When developing a single file self-contained WPF application using .NET 8 that uses the WebView2 component, a folder is created under %temp%\.net while the application is running.

What is the purpose of this folder, when and how is it created, and is it possible or needed to clean up this folder when the application is closed?

2 answers

Your answer

Answer 1

Hongrui Yu-MSFT 5,255 Microsoft External Staff

Hi, @Theiss, Daniel. Welcome to Microsoft Q&A.

Purpose

WebView2 applications use the user data folder (UDF) to store browser data (such as cookies, permissions, and cached resources), which WebView2 could use to speed up the program.

When and how to create

The user data folder (UDF) is created for your WebView2 host app by the WebView2 control. The UDF is created in the default UDF location for the platform, or if your host app specifies a custom UDF location, the UDF is created in the custom UDF location. The UDF is created on startup of the WebView2 host app, if the UDF doesn't exist.

Can or need to clean this folder

If the folder currently takes up too much space, you could clear this folder. For example, clear the contents of a folder when it reaches a specified size.

        private async Task ClearAutofillData()
        {
            double cleanSize = 10;
            var userDataFolder = "The address of your UDF folder";

            DirectoryInfo dirInfo = new DirectoryInfo(userDataFolder);
            double folderSize = dirInfo.GetFiles("*", SearchOption.AllDirectories).Sum(file => file.Length) / (1024.0 * 1024.0);

            if (folderSize >= cleanSize )
            {
                CoreWebView2Profile profile;
                if (MyWebView2.CoreWebView2 != null)
                {
                    profile = MyWebView2.CoreWebView2.Profile;
                    await profile.ClearBrowsingDataAsync();
                }
            }
        }

For a more detailed description of this folder, you could refer to the official documentation：

1.https://learn.microsoft.com/en-us/microsoft-edge/webview2/concepts/user-data-folder?tabs=dotnet#what-kind-of-data-is-stored-in-the-udf

2.https://learn.microsoft.com/en-us/microsoft-edge/webview2/concepts/clear-browsing-data?tabs=csharp

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Theiss, Daniel 0

Thank you a lot for your answer.

However, I do not mean the UDF folder of WebView2, but a folder that is also created in %temp%.net.

This contains e.g. the following content:

C:\Users\MyUser> dir "C:\Users\MyUser\AppData\Local\Temp\.net\MyApp\FmnNlSANrD4DjMjxZ027s9k+yv1T8uI=" -Recurse

    Directory: C:\Users\MyUser\AppData\Local\Temp\.net\MyApp\FmnNlSANrD4DjMjxZ027s9k+yv1T8uI=

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----          12.02.2025    17:15                runtimes
-a---          25.03.2025    13:50        4916840 D3DCompiler_47_cor3.dll
-a---          25.03.2025    13:50         157992 PenImc_cor3.dll
-a---          25.03.2025    13:50        1237280 PresentationNative_cor3.dll
-a---          25.03.2025    13:50         160040 sni.dll
-a---          25.02.2025    10:50         120184 vcruntime140_cor3.dll
-a---          25.03.2025    13:50         165336 WebView2Loader.dll
-a---          25.03.2025    13:50        1959728 wpfgfx_cor3.dll

    Directory: C:\Users\MyUser\AppData\Local\Temp\.net\MyApp\FmnNlSANrD4DjMjxZ027s9k+yv1T8uI=\runtimes

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----          12.02.2025    17:15                win-x64

    Directory: C:\Users\MyUser\AppData\Local\Temp\.net\MyApp\FmnNlSANrD4DjMjxZ027s9k+yv1T8uI=\runtimes\win-x64

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
d----          25.03.2025    13:50                native

    Directory: C:\Users\MyUser\AppData\Local\Temp\.net\MyApp\FmnNlSANrD4DjMjxZ027s9k+yv1T8uI=\runtimes\win-x64\native

Mode                 LastWriteTime         Length Name
----                 -------------         ------ ----
-a---          25.03.2025    13:50         165336 WebView2Loader.dll

I can't find any help on this folder in the .NET documentation.

Can you tell me anything about this folder?

Hongrui Yu-MSFT 5,255 Reputation points Microsoft External Staff

2025-03-31T08:50:38.91+00:00

Hi, @Theiss, Daniel.

Generally speaking, the contents in the C:\Users\MyUser\AppData\Local\Temp directory are temporary files, which are used to store short-term data required during program operation. Generally, developers also write temporary data required during program operation to the Temp directory. During operation, the WebView2 component will create temporary files in Temp as needed to complete a certain function. When the program is closed, these files usually lose their use and could be deleted.
Theiss, Daniel 0 Reputation points

2025-03-31T08:58:22.0433333+00:00

Hi, @Hongrui Yu-MSFT ,

We have to evaluate the content of this folder within a threat model process. Unfortunately, this information is not enough for me. Who could I contact if I need more detailed information?
Hongrui Yu-MSFT 5,255 Reputation points Microsoft External Staff

2025-03-31T09:26:06.85+00:00

Hi, @Theiss, Daniel.

For more detailed information about WebView2, you could view the source code of WebView2. Since Microsoft Edge has the same source as WebView2, search for Microsoft Edge in the link to view the source code. Related Documents.
Theiss, Daniel 0 Reputation points

2025-04-01T06:25:59.32+00:00

Hi @Hongrui Yu-MSFT ,
Another assumption:

Could it also be that the folder %temp%\.net is used because my application is published as a single file and self-contained?
Hongrui Yu-MSFT 5,255 Reputation points Microsoft External Staff

2025-04-01T09:43:42.54+00:00

Hi, @Theiss, Daniel.

Is your current problem solved? According to the description in the official documentation you provided, IncludeNativeLibrariesForSelfExtract and IncludeAllContentForSelfExtract will extract files to the directory under %TEMP%/.net after being used in the Windows environment, which is similar to your situation.
Theiss, Daniel 0 Reputation points

2025-04-02T10:33:02.2566667+00:00

Hi, @Hongrui Yu-MSFT

Yes, that solves my current problem. I just edited my answer to describe the purpose of the folder. Now I can try to mitigate to delete the contents of the folder when my application quits.

Answer 2

Theiss, Daniel 0

Hi, @Hongrui Yu-MSFT
Sometimes it is enough to talk to someone to get new ideas of what to look for.

I found the corresponding place in the Microsoft documentation: Single-File Deploykment | Native Libraries

The folder %temp%\.net is needed because we are using native libraries (in our case the WebView2 component) in a single file deployment.

This folder is used to extract the native libraries from the single executable and load them into memory.

Many thanks for your support!

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Understanding %temp%\.net Folder | WPF | Single File | Self Contained | WebView2

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