Capturing Localhost Traffic

While testing my application the traffic sent to localhost or 127.0.0.1 is not captured by Fiddler Everywhere system capturing. How can I handle this issue?

Solution

Some frameworks (like .NET) are not proxying the localhost traffic. To solve that issue, you can utilize either of the following approaches:

• Use the machine name instead of localhost.
• Use one of the specially provided aliases in Fiddler Everywhere.

Both solutions require you to enable the Capturing mode.

Using the Machine Name

Use the machine name as an alias for localhost or the 127.0.0.1 loopback addresses. For example, if the machine name is myrootuserid, replace http://localhost:8081/mytestpage.aspx with http://myrootuserid:8081/mytestpage.aspx in the Shell.

Using Aliases

Depending on the specific scenario, you can replace localhost or 127.0.0.1 with one of the following special Fiddler aliases:

• ipv4.fiddler for connections using Internet Protocol version 4.
• ipv6.fiddler for connections using Internet Protocol version 6.
• localhost.fiddler to hit localhost in the Host header (applicable for IIS Express).

For example, traffic sent to the following URL may not be captured:

http://localhost:8081/mytestpage.aspx

To capture that traffic with Fiddler Everywhere, use any of the following approaches:

• Replace localhost with the ipv4.fiddler alias to hit localhost on an IPv4 adapter:

http://ipv4.fiddler:8081/mytestpage.aspx

• Replace localhost with the ipv6.fiddler alias to hit localhost on an IPv6 adapter:

http://ipv6.fiddler:8081/mytestpage.aspx

• Replace localhost with the localhost.fiddler alias to hit localhost in the Host header:

http://localhost.fiddler:8081/mytestpage.aspx

Filtering Localhost Traffic

While using one of the above solutions to capture localhost requests, the traffic will be captured in the Live Traffic grid, and the loopback address will be displayed as a host name, usually 127.0.0.1. To filter by the Host column so that only localhost traffic is displayed, enter the loopback address, and not the aliases used in the browsers, as a host value.

Additional Resources

• Learn how to direct localhost requests from the mobile application through the Fiddler proxy...

If you have more questions or need help capturing localhost traffic with Fiddler Everywhere, you can reach out to our support team through the Contact Support option.