Filter Fiddler traffic using domain names and client processes

This article explains how to filter traffic that's captured by Fiddler using domain/host names owned by Microsoft Entra and client processes.

Prerequisites

Before filtering, ensure that Fiddler is configured to capture traffic for all processes. In the lower-left corner of the Fiddler window, you can select All processes to change the selection.

Filter traffic using Fiddler's built-in filter feature

To filter traffic using Fiddler's built-in filter feature, follow these steps:

1. Open Fiddler and navigate to the right panel.

2. Select the Filters tab, and then select the Use Filters checkbox.

3. Under the Hosts section, select Show only the following Hosts.

4. In the text box, enter the host name list you want to filter on, separated by semicolons, for example, localhost;login.microsoftonline.com;graph.microsoft.com.

   Note

   This text box will display a yellow background while editing the list, indicating unsaved changes.

5. Select the Actions button to save the list. The background color will change to white, confirming the list is saved.

Under the Client Process section, you can also select a specific process to filter on. This is particularly useful for filtering a standalone application. It might be less effective for capturing browser traffic because multiple processes with the same name can make it difficult to identify the correct one.

Filter traffic using JavaScript code in the OnBeforeRequest function

Note

This option is used especially for browser-based applications.

1. In Fiddler, go to Rules > Customize Rules. This action will open the CustomRules.js file in the FiddlerScript editor.

2. Locate the OnBeforeRequest function in the FiddlerScript editor.

3. Insert the following JavaScript code at the beginning of the function:

   // begin filter
   
   // set this to false to disable filter and true to enable filter
   var filterOn = true;
   
   if (filterOn)
   {
       // hide all requests by default
       oSession["ui-hide"] = "true";
   
       // list of domain names to filter on
       var host = ["localhost", "login.microsoftonline.com", "graph.microsoft.com"];
   
       // list of processes to filter on
       var processlist = ["chrome", "microsoftedgecp", "iisexpress", "powershell"];
   
       for (var j = 0; j < processlist.length; j++)
       {
           if (oSession.LocalProcess.Contains(processlist[j]))
           {
               for (var i = 0; i < host.length; i++)
               {
                   if (oSession.HostnameIs(host[i]))
                   {
                       oSession["ui-hide"] = null;
                   }
               }
           }
       }
   }
   
   // end filter
   

   

   Here are the explanations of some variables in the JavaScript code:

   • filterOn: Set it to true to enable the filter and false to disable it.
   • host: Contains the list of domain names to filter on.
   • processlist: Contains the list of process names to filter on.

4. Save the changes to the CustomRules.js file.

References

• Modifying a Request or Response
• FiddlerScript Cookbook
• Understanding FiddlerScript

Third-party information disclaimer

The third-party products that this article discusses are manufactured by companies that are independent of Microsoft. Microsoft makes no warranty, implied or otherwise, about the performance or reliability of these products.

Contact us for help

If you have questions or need help, create a support request, or ask Azure community support. You can also submit product feedback to Azure feedback community.