Quickstart: Debug ASP.NET Core with the Visual Studio debugger

In this Quickstart, you explore how to use the Visual Studio debugger to you debug your ASP.NET Core application code. This article provides a quick way to learn some of the basic features for working in the debugger.

If you don't have Visual Studio, you can install the free trial version from the Visual Studio Downloads page.

Create a new project

Start by creating a new project, so you have some code to check in the debugger.

1. Open Visual Studio and create a new project.

   • If the Start Window isn't open, select File > Start Window.

   • In the Start Window, select Create a new project.

2. In the Create a new project window, set the filters and search for a project template.

   • In the Search for templates box, enter web app.

   • Expand the Language dropdown and select C#.

3. In the list of results, select the ASP.NET Core Web App (Razor Pages) template for C#, and then select Next.

   If you don't see the ASP.NET Core Web App (Razor Pages) template for C#, select the Continue without code option.

   1. Select Tools > Get Tools and Features..., which opens the Visual Studio Installer.

   2. In the Installer window, select the checkbox for the ASP.NET and web development workload, and then select Modify.

      Your Visual Studio installation updates to include the selected ASP.NET workload.

   3. After the update completes, select File > Start Window, and follow the previous instructions to select the required template.

4. Configure the new project:

   1. Enter a Project name and Solution name, or use the default values.

   2. Use the default Location or select browse (...) to create the project in a different folder.

   3. Select Next.

   4. Use the recommended target Framework (the default is .NET 10.0 Long Term Support).

   5. For the other settings, use the default values.

   6. Select Create.

   Visual Studio creates your new project and adds the project files in the specified folder.

Update the project code

Update some of the code supplied by the project template so you have more statements to test in the debugger.

1. In the Solution Explorer pane, expand the <project-name>\Pages node, and select the Privacy.cshtml item.

   The Privacy.cshtml file opens in the code editor.

2. Locate the following section of code in the file and replace it with the provided snippet:

   @{
    ViewData["Title"] = "Privacy Policy";
   }
   

   Replacement snippet:

   @{
    ViewData["Title"] = "Privacy Policy";
    <label>@PrivacyModel.PrivacyMessage</label>
   }
   

3. In Solution Explorer, expand the <project-name>\Pages\Privacy.cshtml node, and select the Privacy.cshtml.cs item.

   The Privacy.cshtml.cs file opens in the code editor.

4. Locate the following section of code in the file and replace it with the provided snippet:

   public void OnGet()
   {
   }
   

   Replacement snippet:

   
   public static string? PrivacyMessage { get; set; }
   
   public void OnGet() {
      LinkedList<int> result = DoWork();
   
      PrivacyMessage = "Result of work: " + result.First.Value + ", " + result.First.Value;
   }
   
   private static LinkedList<int> DoWork() {
      LinkedList<int> c1 = new();
   
      c1.AddLast(10);
      c1.AddLast(20);
   
      LinkedList<int> c2 = new(c1);
      return c2;
   }
   

Set a breakpoint

A breakpoint is a marker that indicates where Visual Studio should suspend your running code. When a breakpoint is set, you can take a look at the current values of variables, examine the behavior of memory, and check if a specific branch of code is running. Breakpoints are the most basic feature in debugging.

1. To set a breakpoint, locate the call to the DoWork function in the code, and then select in the left gutter on the same line.

   When the breakpoint is set, a red dot displays in the left gutter on the corresponding line in the code.

   

   

2. Start debugging by using the F5 keyboard shortcut (or select Debug > Start Debugging).

3. When the web page opens in the browser window, select the Privacy link at the top of the page.

   Code execution pauses immediately before the call to the DoWork function.

   The debugger pauses where you set the breakpoint. A yellow arrow identifies the statement where the debugger pauses app execution.

   

   

Set conditional breakpoints

If you set a breakpoint in a loop or recursion, or if you have many breakpoints that you frequently step through, use a conditional breakpoint.

This approach helps ensure your code is suspended only when specific conditions are met. A conditional breakpoint can save time and also make it easier to debug issues that are hard to reproduce.

Walk through your code

Visual Studio provides several different ways for instructing the debugger to continue with app execution. The following example shows a useful command for walking through your code.

While the code is paused at the breakpoint, hover over the statement return c2; until you see the green Run to click (Run execution to here) icon. Select the icon.

The app continues execution, and pauses on the line of code where you clicked the button.

Common keyboard commands used to step through code include F10 and F11. For more in-depth instructions, see First look at the debugger.

Inspect variables in a data tip

You can inspect the state of your variables by using the data tip feature.

1. In the current line of code (marked by the yellow execution pointer), hover over the c2 object to see the data tip.

   

   

   The data tip shows you the current value of the c2 variable and allows you to inspect its properties.

   When you're debugging, if you see an unexpected value for a variable, you probably have a bug. The bug could be in the code that makes the call to the variable or in the previous line.

2. Expand the data tip to look at the current property values of the c2 object.

3. To continue checking the value of c2 as the code executes, select the pin icon on the data tip.

   The pin action keeps the data tip open. As the code executes, the value in the pinned tip changes to show the current state of the watched object.

   You can move the pinned tip to any location in the IDE, so it doesn't prevent you watching other items while debugging.

Next step