title | author | description | monikerRange | ms.author | ms.custom | ms.date | uid |
---|---|---|---|---|---|---|---|
Debug ASP.NET Core Blazor apps |
guardrex |
Learn how to debug Blazor apps, including debugging Blazor WebAssembly with browser developer tools or an integrated development environment (IDE). |
>= aspnetcore-3.1 |
riande |
mvc |
11/14/2023 |
blazor/debug |
This article describes how to debug Blazor apps, including debugging Blazor WebAssembly apps with browser developer tools or an integrated development environment (IDE).
:::moniker range=">= aspnetcore-8.0"
Blazor Web Apps can be debugged in Visual Studio or Visual Studio Code.
Blazor WebAssembly apps can be debugged:
- In Visual Studio or Visual Studio Code.
- Using browser developer tools in Chromium-based browsers, including Microsoft Edge, Google Chrome, and Firefox.
Available scenarios for Blazor WebAssembly debugging include:
- Set and remove breakpoints.
- Run the app with debugging support in IDEs.
- Single-step through the code.
- Resume code execution with a keyboard shortcut in IDEs.
- In the Locals window, observe the values of local variables.
- See the call stack, including call chains between JavaScript and .NET.
- Use a symbol server for debugging, configured by Visual Studio preferences.
Unsupported scenarios include:
- Debug in non-local scenarios (for example, Windows Subsystem for Linux (WSL) or Visual Studio Codespaces).
- Debug in Firefox from Visual Studio or Visual Studio Code.
:::moniker-end
:::moniker range=">= aspnetcore-6.0 < aspnetcore-8.0"
Blazor Server apps can be debugged in Visual Studio or Visual Studio Code.
Blazor WebAssembly apps can be debugged:
- In Visual Studio or Visual Studio Code.
- Using browser developer tools in Chromium-based browsers, including Microsoft Edge and Google Chrome.
Unsupported scenarios for Blazor WebAssembly apps include:
- Set and remove breakpoints.
- Run the app with debugging support in IDEs.
- Single-step through the code.
- Resume code execution with a keyboard shortcut in IDEs.
- In the Locals window, observe the values of local variables.
- See the call stack, including call chains between JavaScript and .NET.
- Debug in non-local scenarios (for example, Windows Subsystem for Linux (WSL) or Visual Studio Codespaces).
- Use a symbol server for debugging.
:::moniker-end
:::moniker range="< aspnetcore-6.0"
Blazor Server apps can be debugged in Visual Studio or Visual Studio Code.
Blazor WebAssembly apps can be debugged:
- In Visual Studio or Visual Studio Code.
- Using browser developer tools in Chromium-based browsers, including Microsoft Edge and Google Chrome.
Unsupported scenarios for Blazor WebAssembly apps include:
- Set and remove breakpoints.
- Run the app with debugging support in IDEs.
- Single-step through the code.
- Resume code execution with a keyboard shortcut in IDEs.
- In the Locals window, observe the values of local variables.
- See the call stack, including call chains between JavaScript and .NET.
- Hit breakpoints during app startup before the debug proxy is running. This includes breakpoints in the
Program
file and breakpoints in theOnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app. - Debug in non-local scenarios (for example, Windows Subsystem for Linux (WSL) or Visual Studio Codespaces).
- Use a symbol server for debugging.
:::moniker-end
This section explains the prerequisites for debugging.
:::moniker range=">= aspnetcore-8.0"
The latest version of the following browsers:
- Google Chrome
- Microsoft Edge
- Firefox (browser developer tools only)
:::moniker-end
:::moniker range="< aspnetcore-8.0"
Debugging requires the latest version of the following browsers:
- Google Chrome (default)
- Microsoft Edge
:::moniker-end
Ensure that firewalls or proxies don't block communication with the debug proxy (NodeJS
process). For more information, see the Firewall configuration section.
Note
Apple Safari on macOS isn't currently supported.
The latest version of Visual Studio or Visual Studio Code is required.
Visual Studio Code requires the C# Dev Kit for Visual Studio Code (Getting Started with C# in VS Code). In the Visual Studio Code Extensions Marketplace, filter the extension list with "c# dev kit
" to locate the extension:
Installing the C# Dev Kit automatically installs the following additional extensions:
If you encounter warnings or errors, you can open an issue (microsoft/vscode-dotnettools
GitHub repository) describing the problem.
The guidance in this subsection applies to client-side debugging.
Open the Properties/launchSettings.json
file of the startup project. Confirm the presence of the following inspectUri
property in each launch profile of the file's profiles
node. If the following property isn't present, add it to each profile:
"inspectUri": "{wsProtocol}://{url.hostname}:{url.port}/_framework/debug/ws-proxy?browser={browserInspectUri}"
The inspectUri
property:
- Enables the IDE to detect that the app is a Blazor app.
- Instructs the script debugging infrastructure to connect to the browser through Blazor's debugging proxy.
The placeholder values for the WebSocket protocol (wsProtocol
), host (url.hostname
), port (url.port
), and inspector URI on the launched browser (browserInspectUri
) are provided by the framework.
:::moniker range=">= aspnetcore-8.0"
Blazor Web Apps: Microsoft.AspNetCore.Components.WebAssembly.Server
: References an internal package (Microsoft.NETCore.BrowserDebugHost.Transport
) for assemblies that share the browser debug host.
:::moniker-end
:::moniker range="< aspnetcore-8.0"
Blazor Server: Microsoft.AspNetCore.Components.WebAssembly.Server
: References an internal package (Microsoft.NETCore.BrowserDebugHost.Transport
) for assemblies that share the browser debug host.
:::moniker-end
Standalone Blazor WebAssembly: Microsoft.AspNetCore.Components.WebAssembly.DevServer
: Development server for use when building Blazor apps. Calls xref:Microsoft.AspNetCore.Builder.WebAssemblyNetDebugProxyAppBuilderExtensions.UseWebAssemblyDebugging%2A?displayProperty=nameWithType internally to add middleware for debugging Blazor WebAssembly apps inside Chromium developer tools.
:::moniker range="< aspnetcore-8.0"
Hosted Blazor WebAssembly:
- :::no-loc text="Client"::: project:
Microsoft.AspNetCore.Components.WebAssembly.DevServer
: Development server for use when building Blazor apps. Calls xref:Microsoft.AspNetCore.Builder.WebAssemblyNetDebugProxyAppBuilderExtensions.UseWebAssemblyDebugging%2A?displayProperty=nameWithType internally to add middleware for debugging Blazor WebAssembly apps inside Chromium developer tools. - :::no-loc text="Server"::: project:
Microsoft.AspNetCore.Components.WebAssembly.Server
: References an internal package (Microsoft.NETCore.BrowserDebugHost.Transport
) for assemblies that share the browser debug host.
:::moniker-end
:::moniker range=">= aspnetcore-8.0"
The example in this section assumes that you've created a Blazor Web App with an interactive render mode of Auto (Server and WebAssembly) and per-component interactivity location.
- Open the app.
- Set a breakpoint on the
currentCount++;
line in theCounter
component (Pages/Counter.razor
) of the client project (.Client
). - Press F5 to run the app in the debugger.
- In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. - In Visual Studio, inspect the value of the
currentCount
field in the Locals window. - Press F5 to continue execution.
Breakpoints can also be hit in the server project in statically-rendered and interactively-rendered server-side components.
-
Stop the debugger.
-
Add the following component to the server app. The component applies the Interactive Server render mode (
InteractiveServer
).Components/Pages/Counter2.razor
:@page "/counter-2" @rendermode InteractiveServer <PageTitle>Counter 2</PageTitle> <h1>Counter 2</h1> <p role="status">Current count: @currentCount</p> <button class="btn btn-primary" @onclick="IncrementCount">Click me</button> @code { private int currentCount = 0; private void IncrementCount() { currentCount++; } }
-
Set a breakpoint on the
currentCount++;
line in theCounter2
component. -
Press F5 to run the app in the debugger.
-
In the browser, navigate to
Counter2
page at/counter-2
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. -
Press F5 to continue execution.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
The example in this section assumes that you've created a Blazor Web App with Server interactivity.
-
Open the app by opening the project folder.
When opening a new app in Visual Studio Code and the IDE requests that you add assets to build and debug the project, select Yes.
If Visual Studio Code doesn't automatically offer to add build and debug assets (the
.vscode
folder withlaunch.json
andtasks.json
files), select View > Command Palette and type ".NET
" into the search box. From the list of commands, select the ".NET: Generate Assets for Build and Debug
" command. -
Set a breakpoint on the
currentCount++;
line in theCounter
component (Components/Pages/Counter.razor
). -
Press F5 (Start Debugging) to run the app in the debugger.
-
In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. -
Press F5 (Continue) to continue execution.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
Start Without Debugging [Ctrl+F5 (Windows) or ⌘+F5 (macOS)] isn't supported. When the app is run in Debug configuration, debugging overhead always results in a small performance reduction.
:::moniker-end
:::moniker range="< aspnetcore-8.0"
- Open the app.
- Set a breakpoint on the
currentCount++;
line in theCounter
component (Pages/Counter.razor
). - Press F5 to run the app in the debugger.
- In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. - In Visual Studio, inspect the value of the
currentCount
field in the Locals window. - Press F5 to continue execution.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
-
Open the app.
When opening a new app in Visual Studio Code and the IDE requests that you add assets to build and debug the project, select Yes.
If Visual Studio Code doesn't automatically offer to add build and debug assets (the
.vscode
folder withlaunch.json
andtasks.json
files), select View > Command Palette and type ".NET
" into the search box. From the list of commands, select the ".NET: Generate Assets for Build and Debug
" command. -
Set a breakpoint on the
currentCount++;
line in theCounter
component (Pages/Counter.razor
). -
Press F5 to run the app in the debugger.
-
In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. -
Press F5 to continue execution.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
Start Without Debugging [Ctrl+F5 (Windows) or ⌘+F5 (macOS)] isn't supported. When the app is run in Debug configuration, debugging overhead always results in a small performance reduction.
:::moniker-end
- Open the app.
- Set a breakpoint on the
currentCount++;
line in theCounter
component (Pages/Counter.razor
). - Press F5 to run the app in the debugger.
- In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. - In Visual Studio, inspect the value of the
currentCount
field in the Locals window. - Press F5 to continue execution.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
-
Open the standalone Blazor WebAssembly app.
When opening a new app in Visual Studio Code and the IDE requests that you add assets to build and debug the project, select Yes.
If Visual Studio Code doesn't automatically offer to add build and debug assets (the
.vscode
folder withlaunch.json
andtasks.json
files), select View > Command Palette and type ".NET
" into the search box. From the list of commands, select the ".NET: Generate Assets for Build and Debug
" command. -
Set a breakpoint on the
currentCount++;
line in theCounter
component (Pages/Counter.razor
). -
Press F5 to run the app in the debugger.
-
The standalone app is launched, and a debugging browser is opened.
-
In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. -
Press F5 to continue execution.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
Start Without Debugging [Ctrl+F5 (Windows) or ⌘+F5 (macOS)] isn't supported. When the app is run in Debug configuration, debugging overhead always results in a small performance reduction.
:::moniker range="< aspnetcore-8.0"
-
With the :::no-loc text="Server"::: project selected in Solution Explorer, press F5 to run the app in the debugger.
When debugging with a Chromium-based browser, such as Google Chrome or Microsoft Edge, a new browser window might open with a separate profile for the debugging session instead of opening a tab in an existing browser window with the user's profile. If debugging with the user's profile is a requirement, adopt one of the following approaches:
- Close all open browser instances before pressing F5 to start debugging.
- Configure Visual Studio to launch the browser with the user's profile. For more information on this approach, see Blazor WASM Debugging in VS launches Edge with a separate user data directory (dotnet/aspnetcore #20915).
-
In the :::no-loc text="Client"::: project, set a breakpoint on the
currentCount++;
line in theCounter
component (Pages/Counter.razor
). -
In the browser, navigate to
Counter
page at/counter
. Wait a few seconds for the debug proxy to load and run. Select the Click me button to hit the breakpoint. -
In Visual Studio, inspect the value of the
currentCount
field in the Locals window. -
Press F5 to continue execution.
You can also debug server code in the :::no-loc text="Server"::: project:
- Set a breakpoint in the
Pages/FetchData.razor
page in xref:Microsoft.AspNetCore.Components.ComponentBase.OnInitializedAsync%2A. - Set a breakpoint in the
WeatherForecastController
in theGet
action method. - Browse to the
Fetch Data
page to hit the first breakpoint in theFetchData
component just before it issues an HTTP request to the server. - Press F5 to continue execution and then hit the breakpoint on the server in the
WeatherForecastController
. - Press F5 again to let execution continue and see the weather forecast table rendered in the browser.
Breakpoints are not hit during app startup before the debug proxy is running. This includes breakpoints in the Program
file and breakpoints in the OnInitialized{Async}
lifecycle methods of components that are loaded by the first page requested from the app.
Start Without Debugging [Ctrl+F5 (Windows) or ⌘+F5 (macOS)] isn't supported. When the app is run in Debug configuration, debugging overhead always results in a small performance reduction.
When opening a new app in Visual Studio Code and the IDE requests that you add assets to build and debug the project, select Yes.
If Visual Studio Code doesn't automatically offer to add build and debug assets (the .vscode
folder with launch.json
and tasks.json
files), select View > Command Palette and type ".NET
" into the search box. From the list of commands, select the ".NET: Generate Assets for Build and Debug
" command for the :::no-loc text="Server"::: project.
Note
Only browser debugging is supported at this time.
You can't automatically rebuild the backend :::no-loc text="Server"::: project of a hosted Blazor WebAssembly solution during debugging, for example by running the app with dotnet watch run
.
To debug a published, hosted Blazor WebAssembly app, configure debugger support (DebuggerSupport
) and copy output symbols to the publish
directory (CopyOutputSymbolsToPublishDirectory
) in the :::no-loc text="Client"::: project's project file:
<DebuggerSupport>true</DebuggerSupport>
<CopyOutputSymbolsToPublishDirectory>true</CopyOutputSymbolsToPublishDirectory>
By default, publishing an app disables the preceding properties by setting them to false
.
Warning
Published, hosted Blazor WebAssembly apps should only enable debugging and copying output symbols when deploying published assets locally. Do not* deploy a published app into production with the DebuggerSupport
and CopyOutputSymbolsToPublishDirectory
properties set to true
.
Start Without Debugging [Ctrl+F5 (Windows) or ⌘+F5 (macOS)] isn't supported. When the app is run in Debug configuration, debugging overhead always results in a small performance reduction.
:::moniker-end
To attach to a running Blazor app, open the .vscode/launch.json
file and replace the {URL}
placeholder with the URL where the app is running:
{
"name": "Attach and Debug",
"type": "blazorwasm",
"request": "attach",
"url": "{URL}"
}
The launch configuration options in the following table are supported for the blazorwasm
debug type (.vscode/launch.json
).
Option | Description |
---|---|
browser |
The browser to launch for the debugging session. Set to edge or chrome . Defaults to edge . |
cwd |
The working directory to launch the app under. |
request |
Use launch to launch and attach a debugging session to a Blazor WebAssembly app or attach to attach a debugging session to an already-running app. |
timeout |
The number of milliseconds to wait for the debugging session to attach. Defaults to 30,000 milliseconds (30 seconds). |
trace |
Used to generate logs from the JS debugger. Set to true to generate logs. |
url |
The URL to open in the browser when debugging. |
webRoot |
Specifies the absolute path of the web server. Should be set if an app is served from a sub-route. |
:::moniker range="< aspnetcore-8.0"
The additional options in the following table only apply to hosted Blazor WebAssembly apps.
Option | Description |
---|---|
env |
The environment variables to provide to the launched process. Only applicable if hosted is set to true . |
hosted |
Must be set to true if launching and debugging a hosted Blazor WebAssembly app. |
program |
A reference to the executable to run the server of the hosted app. Must be set if hosted is true . |
:::moniker-end
The guidance in this section applies debugging Blazor WebAssembly apps in:
- Google Chrome running on Windows or macOS.
- Microsoft Edge running on Windows.
-
Run the app in a command shell with
dotnet run
. -
Launch a browser and navigate to the app's URL.
-
Start remote debugging by pressing:
- Shift+Alt+d on Windows.
- Shift+⌘+d on macOS.
The browser must be running with remote debugging enabled, which isn't the default. If remote debugging is disabled, an Unable to find debuggable browser tab error page is rendered with instructions for launching the browser with the debugging port open. Follow the instructions for your browser.
After the app opens in a new browser tab, start remote debugging by pressing:
- Shift+Alt+d on Windows.
- Shift+⌘+d on macOS.
-
After the new developer tools browser tab opens showing a ghosted image of the app, return to the app's browser tab.
-
Open the browser's developer tools console.
-
After a moment, the Sources tab shows a list of the app's .NET assemblies and pages.
-
Open the
file://
node. In component code (.razor
files) and C# code files (.cs
), breakpoints that you set are hit when code executes. After a breakpoint is hit, single-step (F10) through the code or resume (F8) code execution normally.
For Chromium-based browser debugging, Blazor provides a debugging proxy that implements the Chrome DevTools Protocol and augments the protocol with .NET-specific information. When debugging keyboard shortcut is pressed, Blazor points the Chrome DevTools at the proxy. The proxy connects to the browser window you're seeking to debug (hence the need to enable remote debugging).
:::moniker range=">= aspnetcore-8.0"
The guidance in this section applies debugging Blazor WebAssembly apps in Firefox running on Windows.
Debugging a Blazor WebAssembly app with Firefox requires configuring the browser for remote debugging and connecting to the browser using the browser developer tools through the .NET WebAssembly debugging proxy.
Note
Debugging in Firefox from Visual Studio isn't supported at this time.
To debug a Blazor WebAssembly app in Firefox during development:
- Run the app in a command shell with
dotnet run
. - Navigate to the app in Firefox.
- Open the Firefox Web Developer Tools and go to the
Console
tab. - With app in focus by selecting the app's UI in the browser's window, start remote debugging by pressing Shift+Alt+d.
- Follow the instructions in the console output to configure Firefox for Blazor WebAssembly debugging:
- Open
about:config
in a new browser tab. Read and dismiss the warning that appears. - Enable
devtools.debugger.remote-enabled
. - Enable
devtools.chrome.enabled
. - Disable
devtools.debugger.prompt-connection
.
- Open
- Close all Firefox instances.
- Navigate to Firefox's executable location with the following command in a command shell:
cd "C:\Program Files\Mozilla Firefox"
(include the quotes). - Execute the following command:
.\firefox.exe --start-debugger-server 6000 -new-tab about:debugging
. - In the new Firefox instance, an
about:debugging
tab opens. Leave this tab open. - Open a new browser tab and navigate to the Blazor WebAssembly app.
- Press Shift+Alt+d to open the Firefox Web Developer tools and connect to the Firefox browser instance.
- In the
Debugger
tab, open the app source file you wish to debug under thefile://
node and set a breakpoint. For example, set a breakpoint in theIncrementCount
method of theCounter
component (Counter.razor
). - Navigate to the
Counter
component page (/counter
) and select the counter button to hit the breakpoint. - Press F5 to continue execution.
:::moniker-end
The debugger doesn't break on unhandled exceptions by default because Blazor catches exceptions that are unhandled by developer code.
To break on unhandled exceptions:
- Open the debugger's exception settings (Debug > Windows > Exception Settings) in Visual Studio.
- Set the following JavaScript Exceptions settings:
- All Exceptions
- Uncaught Exceptions
Browser source maps allow the browser to map compiled files back to their original source files and are commonly used for client-side debugging. However, Blazor doesn't currently map C# directly to JavaScript/WASM. Instead, Blazor does IL interpretation within the browser, so source maps aren't relevant.
If a firewall blocks communication with the debug proxy, create a firewall exception rule that permits communication between the browser and the NodeJS
process.
Warning
Modification of a firewall configuration must be made with care to avoid creating security vulnerabilities. Carefully apply security guidance, follow best security practices, and respect warnings issued by the firewall's manufacturer.
Permitting open communication with the NodeJS
process:
- Opens up the Node server to any connection, depending on the firewall's capabilities and configuration.
- Might be risky depending on your network.
- Is only recommended on developer machines.
If possible, only allow open communication with the NodeJS
process on trusted or private networks.
For Windows Firewall configuration guidance, see Create an Inbound Program or Service Rule. For more information, see Windows Defender Firewall with Advanced Security and related articles in the Windows Firewall documentation set.
If you're running into errors, the following tips may help:
- Remove breakpoints:
- Google Chrome: In the Debugger tab, open the developer tools in your browser. In the console, execute
localStorage.clear()
to remove any breakpoints. - Microsoft Edge: In the Application tab, open Local storage. Right-click the site and select Clear.
- Google Chrome: In the Debugger tab, open the developer tools in your browser. In the console, execute
- Confirm that you've installed and trusted the ASP.NET Core HTTPS development certificate. For more information, see xref:security/enforcing-ssl#troubleshoot-certificate-problems-such-as-certificate-not-trusted.
- Visual Studio requires the Enable JavaScript debugging for ASP.NET (Chrome and Edge) option in Tools > Options > Debugging > General. This is the default setting for Visual Studio. If debugging isn't working, confirm that the option is selected.
- If your environment uses an HTTP proxy, make sure that
localhost
is included in the proxy bypass settings. This can be done by setting theNO_PROXY
environment variable in either:- The
launchSettings.json
file for the project. - At the user or system environment variables level for it to apply to all apps. When using an environment variable, restart Visual Studio for the change to take effect.
- The
- Ensure that firewalls or proxies don't block communication with the debug proxy (
NodeJS
process). For more information, see the Firewall configuration section.
The Blazor framework's debugging proxy doesn't launch instantly on app startup, so breakpoints in the OnInitialized{Async}
lifecycle methods might not be hit. We recommend adding a delay at the start of the method body to give the debug proxy some time to launch before the breakpoint is hit. You can include the delay based on an if
compiler directive to ensure that the delay isn't present for a release build of the app.
xref:Microsoft.AspNetCore.Components.ComponentBase.OnInitialized%2A:
protected override void OnInitialized()
{
#if DEBUG
Thread.Sleep(10000);
#endif
...
}
xref:Microsoft.AspNetCore.Components.ComponentBase.OnInitializedAsync%2A:
protected override async Task OnInitializedAsync()
{
#if DEBUG
await Task.Delay(10000);
#endif
...
}
If Visual Studio throws an exception that the debug adapter failed to launch mentioning that the timeout was reached, you can adjust the timeout with a Registry setting:
VsRegEdit.exe set "<VSInstallFolder>" HKCU JSDebugger\Options\Debugging "BlazorTimeoutInMilliseconds" dword {TIMEOUT}
The {TIMEOUT}
placeholder in the preceding command is in milliseconds. For example, one minute is assigned as 60000
.