Build a Custom Inspector

Updated on Nov 6, 2025
  1. Create a Fiddler Classic extension project.

  2. Change the code to derive from the Inspector2 class and implement either IResponseInspector2 or IRequestInspector2.

    c#
    using Fiddler;
    
    [assembly: Fiddler.RequiredVersion("2.3.0.0")]
    
    public class WebViewer: Inspector2, IResponseInspector2
    {
    	public WebViewer()
    	{
    	//
    	// TODO: Add constructor logic here
    	//
    	}
    }
  3. Inside the class, create a new method. By typing public override, you'll get an autocomplete list of the methods you need to write.

  4. In Solution Explorer, right-click on the project and click Add > User Control.

  5. Use the Toolbox to add controls to your user control. These will show the data about the HTTP message under inspection.

  6. In the body{ set } and headers{ set } properties, you should update your control's visual representation of the request or response.

  7. Compile and load your extension in Fiddler.

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