How do I get Fiddler to stop ignoring traffic to localhost?

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When using Fiddler to monitor HTTP Requests & Responses in Internet Explorer it ignores all traffic directed to http://localhost.

Whey answered 18/10, 2008 at 1:1 Comment(4)

I think this is only a problem in IE < 9, right? – Sanguinaria 18/7, 2014 at 15:22

Hum... my localhost traffic is not ignored by defaults and i test it with IE 11 too. – Broderic 17/4, 2015 at 21:35

I also had to switch from IIS to IIS Express – Cist 13/3, 2017 at 14:49

Fiddler used to be this great tool, but now it's just a configuration nightmare. – Understudy 26/1, 2018 at 19:42

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To get Fiddler to capture traffic when you are debugging on local host, after you hit F5 to begin degugging change the address so that localhost has a "." after it.

For instance, you start debugging and the you have the following URL in the Address bar:

http://localhost:49573/Default.aspx

Change it to:

http://localhost.:49573/Default.aspx

Hit enter and Fidder will start picking up your traffic.

Whey answered 18/10, 2008 at 1:2 Comment(5)

Sweetness. So simple and effective. – Ambrosane 20/1, 2011 at 16:38

that works for cassini.. not iis which you need to use if you are connecting to a site or service on SSL... – Aristaeus 8/6, 2011 at 18:22

Nice! Worked perfectly - can't get any simpler. – Inhibitory 4/1, 2012 at 6:8

Didn't work for me using cygwin and curl with the following command: curl -X POST -H "application/json" -d '{"name":{"firstName":"eli", "lastName":"kool"}}' localhost.:61444/Inbound/Catch – Fulgurant 10/6, 2014 at 14:10

WebAPI does not work with localhost. it says Bad Request - Invalid Hostname – Lir 27/5, 2016 at 7:27

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Fiddler's website addresses this question directly.

There are several suggested workarounds, but the most straightforward is simply to use the machine name rather than "localhost" or "127.0.0.1":

http://machinename/mytestpage.aspx

Calle answered 18/10, 2008 at 1:39 Comment(5)

Not sure why Fiddler's website does not suggest the "adding a period after localhost" suggestion, which I think is the best one. This is especially true in some server environments I work in where localhost is the only thing I can use (due to ActiveX controls, permissions, and whatnot). – Sanguinaria 18/7, 2014 at 15:21

@JoshMouch Because some webservers reject localhost. as an invalid hostname. – Hetrick 18/1, 2017 at 21:49

localhost. and machinename is rejected in my case. – Understudy 26/1, 2018 at 19:43

As noted, "localhost." doesn't work on many APIs (or 127.0.0.1). I used the "localhost.fiddler" modification which worked perfectly for me. – Mihrab 7/5, 2019 at 14:12

MachineName is preferred for my some cases, 127.0.0.1 can be refused by IIS – Kelson 2/8, 2022 at 11:44

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Fiddler v4.5.1.0 will allow you to go to replace "localhost" with "localhost.fiddler", and present localhost as the host name for the receiving server running on your machine.

This avoids "host not recognised" errors when connecting to WCF services with the built in web server that visual studio uses.

i.e. Instead of http://localhost:51900/service.wcf you can use http://localhost.fiddler:51900/service.wcf

Bronco answered 18/8, 2015 at 12:34 Comment(2)

WORKS PERFECTLY!.. Due to my work's network configuration none of the other suggestions worked. This is the only trick that worked for me. – Sopher 24/5, 2018 at 14:35

@Sopher Good to hear. :) – Bronco 24/5, 2018 at 14:43

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The correct answer is that it's not that Fiddler ignores traffic targeted at Localhost, but rather that most applications are hardcoded to bypass proxies (of which Fiddler is one) for requests targeted to localhost.

Hence, the various workarounds available: http://fiddler2.com/documentation/Configure-Fiddler/Tasks/MonitorLocalTraffic

Messinger answered 9/5, 2009 at 4:10 Comment(5)

as of April 2013: fiddler2.com/documentation/Configure-Fiddler/Tasks/… p.s. thanks for the awesome tool Eric. – Megmega 15/4, 2013 at 16:45

The adding-a-period-to-the-end-of-localhost is the best trick, and fiddler's site doesn't mention that one. – Sanguinaria 18/7, 2014 at 15:23

Tried the other various solutions on this page: Adding a period, changing the hostname from 'localhost" to my machine name. Neither worked. Replacing "localhost" with "ipv4.fiddler", mentioned in the workarounds document, worked. – Jagged 13/3, 2015 at 5:5

In situations where the address is encoded in the project files that sit in a source code library, distributed to all devs (think Mercurial/Git) in a team, or that all dev's don't actually have fiddler these solutions are unrealistic and cause more problems than they solve. What is needed is a way for fiddler to operate that is outside of a project and therefore have zero impact on taht project or its configuration. – Decree 5/8, 2016 at 12:0

True in my case. I sent a SOAP HTTP request using SOAP-UI, Fiddler 4 wasn't getting it. Then I sent the same HTTP request using POSTMAN and successfully got it – Kopeck 11/12, 2020 at 11:5

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Internet Explorer has a new feature since IE9 RC: adding <-loopback> to the proxy bypass list causes WinInet (the network library used by IE) to send requests destined for localhost and 127.0.0.1 through the defined proxy.

Here's the original announcement by @EricLaw: http://blogs.msdn.com/b/fiddler/archive/2011/02/10/fiddler-is-better-with-internet-explorer-9.aspx

Pedology answered 11/2, 2011 at 10:43 Comment(0)

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For Fiddler to capture traffic from localhost on local IIS, there are 3 steps (It worked on my computer):

Click Tools > Fiddler Options. Ensure Allow remote clients to connect is checked. Close Fiddler.

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Create a new DWORD named ReverseProxyForPort inside KEY_CURRENT_USER\SOFTWARE\Microsoft\Fiddler2. Set the DWORD to port 80 (choose decimal here). Restart Fiddler.

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Add port 8888 to the addresses defined in your client. For example localhost:8888/MyService/WebAPI/v1/

Mckibben answered 26/9, 2014 at 14:53 Comment(2)

Yes, this settings makes the fiddler running as reverse proxy, such that it forwards inbound requests to a different port. In this example it forwards requests made to port 8888 to 80. – Mckibben 18/4, 2015 at 14:24

The most complex to me was to fully ignore localhost and send all the other traffic to being processed by fiddler. You must bypass localhost, BUT also, exclude it withing your functions. (you can try with hide 304 rule for testing purpose.). So i ended excluding it the following way

if ((m_EnableProxy) &&  !(oSession.host =="127.0.0.1" || oSession.host =="localhost" || oSession.host =="ipv4.fiddler")) {             oSession["X-OverrideGateway"] = "socks=127.0.0.1:8080";             oSession["ui-backcolor"] = "#EFEF9F";     	}

. This function should be onBeforeRequest. – Broderic 18/4, 2015 at 19:11

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Using Fiddler v4.6 and the default configuration could not see any traffic from 'localhost'. Tried many suggestions here but nothing worked.

Enabled Help -> Troubleshot and could see many more requests. Sessions were marked in a strike-through font and reason given was 'Hidden due to Status Bar> Process Filter.'

Found this reply from Eric Lawrence to person having same problem http://www.telerik.com/forums/fiddler-not-capturing-ios-traffic-even-though-echo-service-works

basically what to do is: Look at the Status Bar across the bottom of the Fiddler window, the second little "tray" in that bar probably says something like "Web Browsers." Click that and then change to "All Processes."

Paraldehyde answered 11/1, 2016 at 11:59 Comment(0)

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You can use http://ipv4.fiddler or http://ipv6.fiddler instead of localhost

Grindelia answered 17/2, 2016 at 4:55 Comment(0)

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Don't use localhost in the url!

http://~~localhost~~:4200/myTestProject

Use like this:

=>=> Click here for further information <=<=

Conchita answered 23/10, 2017 at 13:36 Comment(0)

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make sure Monitor all connections is ticked. it does not work for me maybe port is diffren i need yo see httprequest to my site from gmail my site is on win xp and iis5(my own machine)

Cioban answered 21/4, 2009 at 14:58 Comment(0)

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Use your local IP address (not 127.0.0.1) instead would work, such as 192.16.0.88 etc. Go to cmd.exe and type ipconfig and you will see it.

Maishamaisie answered 15/5, 2010 at 4:3 Comment(1)

It doesn't work. It seems you can't connect to your own IP address locally – Airiness 13/5, 2016 at 15:34

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Windows XP:

Be sure to set to click the settings button for each of the items in the "Dial-up and Virtual Private Network settings" listbox in the "Connections" tab of the "Internet Options" control panel applet.

I noticed that Fiddler would stop using the "LAN settings" configuration once I connected to my VPN. Even if the traffic wasn't going through the VPN.

Limbert answered 11/1, 2010 at 21:53 Comment(0)

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Type ipconfig at the commmand prompt.
It will give you your IPv4 Address
Replace localhost with your IPv4 Address in the Url when hitting the service.

The traffic will show up in Fiddler under your computer's IP address.

Aerobatics answered 14/11, 2018 at 22:42 Comment(0)

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Unfortunately none of the suggestions were helpful

Only complete exclusion of localhost from monitoring with following setting:

Open View Menu
  > Preferences
    > Connections
      > Bypass Fiddler for URLs that start with:
        > localhost;127.0.0.1

Exhilaration answered 16/5, 2022 at 1:10 Comment(1)

Unfortunately that stopped working too. The official guide is useless docs.telerik.com/fiddler-everywhere/knowledge-base/… unless it's for http only. In my case I need to serve over https – Exhilaration 18/5, 2022 at 12:58

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I had same issue. I could make it filter calls from localhost when I disabled first 2 options and put 'localhost' in 'Show only if URL contains'

April answered 15/11, 2023 at 13:33 Comment(0)

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Go to Tools, Fiddler Options ..., select the Connections tab, then make sure Monitor all connections is ticked. Like Antony Scott said, but also make sure that the "Web Sessions" pane is set to "Capturing" and [ "Web Browsers" OR "All Processes" ]. Looks like the default is "Non-Browser".

Ludwig answered 5/2, 2013 at 15:45 Comment(0)

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