Fiddler

Ostensibly this page is about Fiddler but actually it's about debugging web connections. When I say "Fiddler" I mean "Fiddler Classic".

This is a great page: Best Fiddler Alternatives]

What is Fiddler?

It's a desktop app. Fiddler acts as a proxy, it runs on your Windows (or Mac or Linux) desktop and captures traffic going between your browser and a remote website so that you can see what is going on. I remember trying it out a couple times at different jobs but nothing struck me as truly great about it. It's confusing and hard to use.

You can do pretty much the same thing with Wireshark, I think. Fiddler is just tuned for web whereas Wireshark is generic network data capture.

I got as far as putting mitmproxy on a Linux box and pointing my browser at it, but I can't remember why I did that. I just remember that it worked. See docker/mitmproxy on cc-testmaps. It works amazingly well in fact. You have to install a cert in your Firefox browser, so that it trusts mitmproxy for HTTPS traffic. After that, you're good! Amazing. (Did I say that?)

Tips for Fiddler

I need to capture traffic going between my Windows laptop and servers, and in particular I need to capture ArcGIS Pro and MapProxy traffic.

How can I capture traffic between ArcGIS Server and MapProxy? I need the proxy to live on my Linux box. I don't need a proxy for this.

I can't fathom why I don't already see traffic at Mapproxy.

HTTP headers

I need to see them, but they are visible in Chrome.

• F12
• Network tab
• Reload the page, watch all the network activity
• Pick a line in the left pane
• Switch from Preview to Headers in the right pane, there you go.