Fiddler is a free tool that can be used to capture web traffic for troubleshooting an analysis. Fiddler is Atalasoft Support's preferred method for customer log capture/submission as the .SAZ files created by the tool allow us to review the full content of the captured sessions.

NOTE: Fiddler is used to capture web browser client traffic - we occasionally have customers mistakenly assuming that it is a server side tool - needs to be installed on the server. It does not - it needs to be installed on whatever machine you are going to use the browser on to visit the site in question to repro the issue.

Capturing A Fiddler Log For Support

Often times, while assisting customers with troubleshooting, support will request a Fiddler log. Here are the needed steps:

1. Download and install Fiddler (see "Acquiring Fiddler" below)
2. Once you have this tool installed please run it
3. Once Fiddler is running please open a browser and recreate the issue you are reporting to the support staff
4. Once you have reproduced the issue in the web browser please switch back to Fiddler and open the "file" menu and choose "Save -> All Sessions..." and save as a SAZ file
5. Once you have the SAZ file please attach it to your case (if the log file is over 5MiB, please inform support, as we will need to work with you to arrange alternative to attaching to the support case)

Notes

If you are running your application through localhost, you may need to point to "localhost." (with a period) for Fiddler to properly capture the traffic.

If you are troubleshooting a web app that is hosted over HTTPS, please see the section on HTTPS below

Acquiring Fiddler

The first step for using Fiddler is to download and install it. The following link will take you to the official download page for Fiddler. You will be presented with two options - a .NET 2 compatible installer and a .NET 4 compatible installer. Which version is required depends on the .NET runtimes available on the machine being used to browse the site. Generally, use the Fiddler2 link for an installer compatible with Windows 7.0 and earlier, and the Fiddler4 installer for windows 8.0 and newer.

https://www.telerik.com/download/fiddler

After downloading, simply run the installer.

Please note that it's not recommended to capture over SSL if it can be avoided.. you're much better off hosting in non-https for the testing/debugging of an app rather than having to add the cert below.

In order for Fiddler to be able to make sense of encryptd traffic, you will need to allow HTTPS decryption:

By default, Fiddler will capture all web traffic on your machine while it is running. However, if you're troubleshooting on a site that is encrypted using HTTPS, You need to configure Fiddler to decrypt https traffic.

Decryption of HTTPS traffic requires that Fiddler register a special SSL certificate that is not malicious, but it's good practice to disable the cert when not actively using it for HTTPS troubleshooting.

Original Article:
Q10189 - HOWTO: How to use Fiddler to Collect Data