Fiddler: How to Add a Http Verb, a SOAP Action and a Duration Column

Fiddler is a terrific and free web debugger for any browser, system or platform. You can see much information about every http request that is made. But even better, you can set breakpoints and tamper with the content of a request before continuing.

If you are doing web development, you need to know Fiddler. If you are starting web development, you should invest an hour or more to install and learn about Fiddler. It is a very good investment of your time.

How to Add a Http Verb Column

What I’ve missed from the beginning is a column which shows me the http method (POST, PROPFIND, GET, …) of a request. Many thanks to A. Mackert for the following solution:

In Fiddler, select Rules/Customize Rules. Notepad opens, with some predefined custom rule stuff. Scroll down unto class Handlers.
Uncommment the five marked lines and save the file.


If you have an older version, close and reopen Fiddler. Closing and reopeneing is not needed with the latest versions of Fiddler. Look for the new column – called Method at the right and drag it to the left. Voilá, you have a nice column with the http verb.


How to Change the Editor for the CustomRules File

If you want to do more changes than just uncommenting some lines, it is better to use another editor than notepad. To change the editor, go to Tools/Fiddler Options…/ Tools/FiddlerScriptEditor and select your preferred editor. Notepad++ will do well for now. For extended stuff, there is a special FiddlerScript Editor available. The FiddlerScript Editor has got a built in class explorer which helps with Fiddler classes and types.

How to Add a Column for the Duration of the Request

You can add a column which shows the time in seconds from start to end of a request.

With a current Fiddler version (I’m using you must search for the class Handlers in the CustomRules-file and add the following snippet of code to the class:

public static BindUIColumn("Duration", 60)
function CalcDurationCol(oS: Session){
  var result = String.Empty;
  if ((oS.Timers.ServerDoneResponse > oS.Timers.ClientDoneRequest)) {
    var duration = oS.Timers.ServerDoneResponse -
     result = String.Format("{0:0.0000}",
  return result;

In some previous Fiddler version,   you could just search for m_ShowTTLB in the CustomRules-file and set the value to true.

How to Add a Column Containing the Start Time of the Request

In the CustomRules-file, in the class Handlers add the following snippet of code:

public static BindUIColumn("Starttime", 80)
function CalcStarttimeCol(oS: Session){
  var result = oS.Timers.ClientDoneRequest.ToString("HH:mm:ss.ff");
  return result;

The language used in the CustomRules.js is JScript.NET. So you can use all of .Net’s String.Format possibilities to format the output of the added columns.

How to Add a Column for the SOAP Action

I’ve copied this one from KorteAchternaam.

public static BindUIColumn("SOAP", 120)
function FillSoapAction(oS: Session) {
        if ((oS.oRequest != null)
                && (oS.oRequest.headers != null)
                && (oS.oRequest.headers.Exists("SOAPAction"))) {
            var action = oS.oRequest.headers.Item["SOAPAction"];
            return action.replace(/^.*\//, "").replace(/"/, "");
            return String.Empty;

Happy fiddling.