Fiddler Composer Variables What is it? It is a Fiddler add-on to add support for variables in the request composer. How to install? Simply drop CsvHelper.dll and FiddlerComposerVariables.dll in the following folder: %userprofile%\Documents\Fiddler2\Scripts How to use? Add variables in the "Composer Variables" tab. In your composer, replace key information with the variable surrounded by double curly brackets: {{variable}} Run your requests. Change variable value at any time.