Mike Bosch's Blog on .NET

Agile enterprise architecture in .NET, SOA, WCF, WS-*, AJAX, MVC, Sharepoint and more...

Using Fiddler with ASP.NET's default local server

If you've ever done any kind of AJAX debugging, you may have used Fiddler to figure out exactly what is going over the wire.  Fiddler is a neat little tool that let's you analyze the traffic between the browser and the application.  It shows session information, cookies, and a lot more.  One thing that's not clear right away is how to use it with the ASP.NET local server. 

If you run your typical ASP.NET application with the default server, you'll notice that Fiddler is not capturing any traffic.  To remedy this situation, you can simply add a period ('.') to the end of "localhost" in the address bar (http://localhost.:8181/mywebapp).  This will allow you to view your application’s traffic data with Fiddler.

Posted: Oct 09 2007, 12:27 PM by MikeBosch | with 8 comment(s) |
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Ken Cox said:

Interesting tip, but I get:

[Fiddler] Connection to localhost. failed.<BR>Exception Text: No connection could be made because the target machine actively refused it  

# October 9, 2007 1:15 PM

MikeBosch said:

You might also want to check out this post:


If you're using Vista, it may have something to do with IPv6 vs. IPv4.

# October 9, 2007 5:27 PM

Wil Peck said:

Another way around this is to modify your hosts file.

For Example: local

This is not much better than using your computername.  The only difference is you won't have to add a rule to allow access on port 80 in your firewall software.

# October 18, 2007 1:01 PM

samham said:

To solve the error:

[Fiddler] Connection to localhost. failed.

Exception Text: No connection could be made because the target machine actively refused it

Tools -> Fiddler Options -> remove 'enable IPv6'

# February 24, 2008 1:39 PM

Atit said:

Not working with asp.net mvc application

# December 16, 2008 11:20 AM

link building service said:

Can i have a local server in replace of microsoft IIS where i can run my asp.net application.

Best Regards

# March 27, 2010 10:01 AM
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