Add Rules to Fiddler

Customize Rules

To add custom columns to the Fiddler Classic UI, modify requests or responses, test application performance, and a variety of other custom tasks, add rules to Fiddler's JScript.NET CustomRules.js file in FiddlerScript.

1. Click Rules > Customize Rules....

2. Enter FiddlerScript code inside the appropriate function.

3. Save the file.

Fiddler Classic will automatically reload the rules.

Use Additional .NET Assemblies

To use additional .NET assemblies in your script:

1. Click Tools > Options.

2. Click the Extensions tab.

3. Edit the References list.

4. Either:

   • Register the assembly in the GAC; or

   • Copy the assembly to the folder that contains Fiddler.exe.

To use the new assembly's functions without fully-qualifying them, update the #import clause at the top of the script.

Change the JScript Editor Launched from the Rules Menu

1. Click Tools > Options.

2. Edit the Editor string.

Restore Default Rules

1. Delete the CustomRules.js file in %userprofile%\Documents\Fiddler2\Scripts.

2. Restart Fiddler.

Note: Fiddler's default rules are stored in %localappdata%\Programs\Fiddler\Scripts\SampleRules.js.

See Also

• FiddlerScript Reference
• FiddlerScript Editor
• Fiddler Classic SessionFlags