How to Capture Network Logs Using Fiddler

This article explains how to capture network logs using Fiddler, a web debugging tool, for troubleshooting purposes such as when Outlook add-in issues aren't resolved by browser logs or HAR files alone. It is intended for end users who need to gather logs for their support team. The following steps will be reviewed:

 

• What is Fiddler?

 

• Downloading and Installing Fiddler

 

• Configuring Fiddler

 

• Capturing Network Logs

 

• Saving and Sharing Logs

 

REQUIREMENT:

 

You need administrator (install) rights on your machine to install Fiddler and trust its root certificate.

What is Fiddler?

Fiddler is a web debugging proxy that logs all HTTP(S) traffic between your computer and the internet. It allows you to inspect traffic, set breakpoints, and "fiddle" with incoming or outgoing data. Fiddler is particularly useful for diagnosing issues with web applications, APIs, and network services.

Downloading and Installing Fiddler

 

1. Visit the Fiddler website and download the latest version of Fiddler Classic.

 

2. Run the installer and follow the on-screen instructions to complete the installation.

Configuring Fiddler

 

1. Launch Fiddler from your Start menu or desktop shortcut.

 
2.    

   Configure HTTPS traffic:

      
        

   1. Go to 'Tools' > 'Options'.

      
    

 
1.    
        

   2. In the 'HTTPS' tab, check the boxes for 'Capture HTTPS CONNECTs' and 'Decrypt HTTPS traffic'.

      
    

 
1.    
        

   3. Select 'OK' to save the settings.

        

   4. When prompted, follow the on-screen instructions to install and trust the Fiddler Root certificate.

      
    

 

Note:

 

Only trust the Fiddler Root certificate on a machine used exclusively for troubleshooting. Remove the certificate once you're finished capturing logs.

 

3. Ensure that 'File' > 'Capture Traffic' is checked.

Capturing Network Logs

 

1. Reproduce the issue by performing the actions in your application (for example, the Outlook add-in) that are causing the problem.

 

2. Monitor traffic. Fiddler automatically captures all HTTP(S) traffic, and you can see the requests and responses in the main window.

 
3.    

   Filter traffic (optional):

      
        

   1. Use the 'Filters' tab to narrow down the traffic to specific domains or processes.

      
    

 
3.    
        

   2. For example, filter by process name (e.g., OUTLOOK.EXE) to capture only traffic related to Outlook.

      
    

Saving and Sharing Logs

 
1.    

   Save the logs:

      
        

   1. Go to 'File' > 'Save' > 'All Sessions'.

      
    

 
1.    
        

   2. Choose a location to save the log file (usually in .saz format).

      
    

 
2.    

   Share the logs:

      
        

   1. Compress the .saz file into a .zip archive.

        

   2. Share the .zip file with your support team or the relevant stakeholders.