Use .NET Assemblies in FiddlerScript

To use a .NET addon (for this example, a C# addon that modifies the user-agent string):

Add References

1. Close Fiddler.

2. Save the .NET file (for example, this file called UASimulator.cs):

   using System;
   using System.Windows.Forms;
   using Fiddler;
   
   namespace FiddlerUtility{
   
         public class UASimulator {
               string m_sUAString;
               public UASimulator(string s_UAString){
                     m_sUAString = s_UAString;
               }
   
               public bool OverwriteUA(Session oSession){
                     oSession.oRequest["User-Agent"] = m_sUAString;
                     return true;
               }
         }
   }
   

3. In a VS command prompt, go to the folder where the .CS file is found.

4. Enter the command to create a DLL in the VS command prompt. For example:

   csc /target:library /out:c:\UASim.dll UASimulator.cs /reference:"%localappdata%\Programs\Fiddler\fiddler.exe"
   

5. In Fiddler, click Tools > Options.

6. Click the Extensions tab.

7. In the References field, enter the location of the DLL. For example:

   C:\UASim.dll
   

Update Fiddler Classic Rules

Add a rule to Fiddler Classic to update your script. For example:

    import System;
    import System.Windows.Forms;
    import Fiddler;
    import FiddlerUtility;

    class Handlers{

          static var UASim = new UASimulator("Mozilla/12.0");

          static function OnBeforeRequest(oSession:Fiddler.Session){

                UASim.OverwriteUA(oSession);

          }

       static function Main(){

           var today: Date = new Date();      

           FiddlerObject.StatusText = " CustomRules.js was loaded at: " + today;

       }

    }

See Also

• Write code in .NET with the IAutoTamper interface

• Build assemblies to run in both Fiddler Classic v2 and v4