Fiddler – Put a breakpoint in your network traffic…

I’ve been using Fiddler for a while and covered some of the basics in a previous post. I just learned that with Fiddler, you can put a breakpoint on network traffic! It’s “F5” for network packet capture!

Basically, you launch Fiddler and tell it to stop once it’s received the request (F11 keyboard shortcut). Then you can look at this request and even change it. When you’re ready, you can tell Fiddler to send the request on to it’s ultimate destination.

But it doesn’t stop there…

You can either tell Fiddler to just continue, or you can tell it to stop again once it has the response. Then you can inspect and/or change the response before it is returned to the original caller.

So, you can very easily intercept and change the raw bits in the request or the response via Fiddler. Very nice!

But it doesn’t stop there…

Once you’ve intercepted a request, you can tell Fiddler to “replay” the request back to the server. If you combine this with the ability to break on the request or response, then you can use that initial request to try all sorts of different tweaks.

No more writing tons of crazy code just to get the app to send various types of requests to the server. Just use Fiddler!

But it doesn’t stop there…

You can use Fiddler to record a “session” that could later be used as a VS Web Test. Or, you could just have Fiddler replay that who session for you without using VS.

You can use Fiddler to do a WinDiff compare of two request/response sessions.

Fiddler can act as a Proxy Server for requests.

Fiddler can simulate an experience over slow connections.

Fiddler can include custom rules that can do almost anything with the request or Fiddler UI. Change colors of items in the display, change the target endpoint of a request, etc.

Fiddler can be used for performance testing.
http://blogs.iis.net/brian-murphy-booth/archive/2007/03/09/the-biggest-mistake-serviceprincipalname-s.aspx

Fiddler can help you pretend to use another browser by changing the “User Agent” that is sent in the request.

Fiddler is extensible. There are a bunch of add-ons that provide some neat functionality. They can transform the requests, visualize the data, or do syntax highlighting.

But it doesn’t stop there…

[You get the idea]

You can get Fiddler for FREE from http://www.fiddler2.com. It is super easy to use, but super powerful once you get into the advanced features.

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