How to display localhost traffic in Fiddler while debugging an ASP.NET application?

Question

How do I display localhost traffic in Fiddler while debugging an ASP.NET application?

As of IE9, no special tricks are required. http://blogs.msdn.com/b/fiddler/archive/2011/02/10/fiddler-is-better-with-internet-explorer-9.aspx — EricLaw, May 17 '11 at 03:00

score 88 · Accepted Answer · edited Oct 08 '14 at 14:30

88

try using this:

http://ipv4.fiddler/folder

instead of

http://localhost/folder

this also works with ports

http://ipv4.fiddler:12345/folder

Here is link to fiddler documentation

http://docs.telerik.com/fiddler/Configure-Fiddler/Tasks/MonitorLocalTraffic

edited Oct 08 '14 at 14:30

Satyajit

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answered May 05 '09 at 17:59

bendewey

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Note: This is required only for IE, and only IE8 and earlier. <=IE8 was so smart, it KNEW you wouldn't want to use a proxy server for local traffic! So it sees 'localhost' in your url and doesn't bother with your silly proxy server settings, which is how Fiddler hooks in. – Scott Stafford Apr 24 '14 at 18:36

score 52 · Answer 2 · answered Nov 13 '12 at 09:30

52

To make Fiddler work on localhost with IIS Express you should use this form of URL

http://localhost.fiddler:50262/

This puts correct Host header value (localhost) which satisfies IIS Express.

answered Nov 13 '12 at 09:30

mdonatas

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This worked a treat for me trying to use Excel OData feed import from my test site running under Visual Studio/IIS Express. – Keith Hill Mar 01 '13 at 23:10
Was banging my head against the wall, this worked great for me also!! Thanks! – sǝɯɐſ Aug 12 '14 at 20:36
This works for locally hosted IIS express Asp.net web api. cheers. – Raghu Sep 04 '15 at 03:58

score 20 · Answer 3 · answered Aug 27 '10 at 19:52

20

Start Fiddler. Go to Tools--> Fiddler Options. Choose Connections tab. Check the 'USe PAC Script' option.

Now you will be able to monitor local traffic as well

answered Aug 27 '10 at 19:52

akjal

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I had problems adding the . with SSl and our companies proxy, but changing this setting did the trick. Thanks! – AlignedDev Nov 17 '10 at 21:42

score 12 · Answer 4 · answered May 05 '09 at 18:20

12

For an ASP.NET web site project:

1) Right-click the project and select Property Pages
2) Select Start Options
3) Under the Server section, click the "Use custom server" and edit the Base URL by replacing localhost with your computer's name.

answered May 05 '09 at 18:20

Michael Kniskern

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score 7 · Answer 5 · answered Jul 23 '09 at 08:44

7

Probably the easiest way to monitor traffic to localhost is to replace "localhost" with "localhost." in the browser's URL bar. E.g.

http://localhost./MyApp/default.aspx

answered Jul 23 '09 at 08:44

M4N

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Legends · Answer 6 · 2016-06-12T12:48:55.763

Using Fiddler v4:

Check your IE proxy settings

IE->Tools->Internet Options->Connections->Lan Settings

Check your settings in Fiddler:

Fiddler -> Options-> Connections & Https

Check the Fiddler port, default is 8888

In Fiddler-Menu:

File -> Capture Traffic is checked

The following solution worked for me, when using a

HttpClient or
WebClient from inside an ASP.NET application.

Web.config

<system.net>
    <defaultProxy
                enabled = "true"
                useDefaultCredentials = "true">
      <proxy autoDetect="False" bypassonlocal="False" proxyaddress="http://127.0.0.1:8888" usesystemdefault="False" />
    </defaultProxy>

Code:

var resourceServerUri = new Uri("http://localhost.fiddler:YourAppServicePort");
var body = c.GetStringAsync(new Uri(resourceServerUri)).Result;

Check if your request actually reaches fiddler by customizing the Fiddler Rules script

Fiddler->Rules->Customize Rules

and hook into the OnBeforeRequest event:

static function OnBeforeRequest(oSession: Session) {

if (oSession.hostname.Contains("localhost:YourPortNumber")
{
 System.Windows.Forms.MessageBox.Show(oSession.hostname);  
}

Or explicitly by setting a web proxy

WebClient wc = new WebClient();

WebProxy proxy = new WebProxy();
// try one of these URIs
proxy.Address = new Uri("http://127.0.0.1:8888");
proxy.Address = new Uri("http://hostname:8888");
proxy.Address = new Uri("http://localhost.fiddler");
proxy.Address = new Uri("http://ipv4.fiddler");
// https://en.wikipedia.org/wiki/IPv6
proxy.Address = new Uri("http://ipv6.fiddler");

proxy.BypassProxyOnLocal = false; wc.Proxy = proxy;
var b = wc.DownloadString(new Uri(YourResourceServerBaseAddress));

score 3 · Answer 7 · answered Nov 01 '12 at 10:29

3

Checking the "Use PAC Script" in Fiddler Options -> Connections worked for me when using IIS Express within a corporate intranet.

answered Nov 01 '12 at 10:29

David Norris-Hill

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Well not sure what happened, but I recently upgraded fiddler to v4.6.2.2 and the checking "Usa PAC Script" actually stopped fiddler from working. I had to uncheck the option to get things working again... – David Norris-Hill Apr 14 '16 at 15:01

score 3 · Answer 8 · answered May 05 '09 at 18:00

3

Check out this link...the 'workaround' is hacky, but it does work:

Tip for using Fiddler on localhost

answered May 05 '09 at 18:00

Justin Niessner

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I tried that method and it prompts me with an IE credential pop up. I enter my AD user credentials and get a HTTP 401.1 Logon Failed. – Michael Kniskern May 05 '09 at 18:11
I provided an answer with a suggestion in one of comments from the blog post. – Michael Kniskern May 05 '09 at 18:21

long · Answer 9 · 2012-03-14T12:35:57.620

3

You may use PC hostname instead of 127.0.0.1 or localhost

edited Mar 14 '12 at 12:35

answered Mar 14 '12 at 12:20

long

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score 2 · Answer 10 · edited Dec 27 '12 at 12:07

2

One of the possible solutions is remove the proxy settings in IE as follows.

       IE->Tools->Internet Options->Connections->Lan Settings->

disable following

Automatically detect settings
Use automatic configuration script

edited Dec 27 '12 at 12:07

Andrew Barber

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answered Dec 27 '12 at 12:03

user1932039

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score 2 · Answer 11 · answered Apr 22 '10 at 14:46

2

Try with http://127.0.0.1. <-- note the . at the end

So you can still connect to Casini and debug easily (I'm currently debugging page on http://127.0.0.1.:1718/login/Default.aspx ).

answered Apr 22 '10 at 14:46

nikib3ro

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If localhost. answer doesn't work out for you (as it didn't worked out for me) – nikib3ro Apr 22 '10 at 14:47

score 2 · Answer 12 · answered May 05 '09 at 18:00

2

Ensure that in your Fiddler Connections that localhost isn't in the "IE should bypass Fiddler for URLs that start with:" box.

answered May 05 '09 at 18:00

Jordan S. Jones

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The "IE should bypass Fiddler for URLs that start with" is empty. – Michael Kniskern May 05 '09 at 18:04

score 2 · Answer 13 · answered May 05 '09 at 18:03

2

You should uncheck the checkbox:

Bypass proxy server for local addresses

Located at proxy configuration of Internet Explorer.

answered May 05 '09 at 18:03

m_vitaly

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score 1 · Answer 14 · answered May 13 '13 at 15:32

1

If trying to catpure HTTPS traffic on a local machine from BizTalk using Fiddler, try using the WCF Adapter Proxy settings. I used an address of: http://localhost:8888/

answered May 13 '13 at 15:32

charlie.mott

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Mi hijo und dessen Frau had to buy some cat pure because they came home with yet another gato letzte nacht. – B. Clay Shannon-B. Crow Raven Sep 08 '14 at 21:53

How to display localhost traffic in Fiddler while debugging an ASP.NET application?

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