Fiddler Causing Performance to be Worse

[Shaylin]

I am using Fiddler Classic with one of my clients and now that Fiddler has been installed and is running, they are saying performance on our application has become worse. I have never heard this, and have heard the opposite in that that Fiddler has improved performance.

 

What reason could be causing performance to get worse once Fiddler is installed/running?

[Nick Iliev]

Hello Shaylin,

 

Fiddler Classic is an intermediate proxy that stands between the client applications and the online servers. As such, each HTTP request is once going from the client to Fiddler and then once again from Fiddler to the server. That is hardly a reason for worsened performance, but it is important to note that some of the original behavior might change during both handshakes. For example, you can check if Fiddler uses IPv6

and if it has enabled all supported SSL/TLS protocols

Note that Fiddler Classic does not support TLS 1.3, which is another possible reason why a page might not load.

And, of course, apart from a technical reason within Fiddler, you can face an external reason like a firewall or security tool not working well alongside Fiddler Classic.

The best approach to investigate the possible reason is to determine if the worsened performance happens only with specific URLs (that would indicate an issue specific to the server)or if it constantly happens for all traffic (even for basic pages like https://example.com).

 

 

Regards,
Nick Iliev
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