HTTP requests comparing with Fiddler and WinMerge

Fiddler is a great and easy to use tool for viewing network traffic monitoring that is being generated by our applications. It can be downloaded from Telerik’s Website – a company which is currently developing this tool:

At this post we will look at HTTP requests comparing option. Option Compare will be activated in request’s context menu when you select two of them.

Fiddler Compare Option

Fiddler Compare Option

Unfortunately, you will get an error message when you try to use Compare option right now. It says: “Failed to launch comparison tool (Nie można odnaleźć określonego pliku). Please ensure that windiff.exe is installed and in your Path. Would you like to download WinDiff or WinMerge?” But don’t event try to click on Yes button. It will just open Fiddler’s website.

We can find WinMerge application under this website: After downloading just start the installation. I recommend you to check “Plugins” option before while selecting components. It will ease an external script installation in feature.

After finished installation there is nothing to do more. You can use Compare option in Fiddler and it should just work.

A really useful Fiddler feature is request marking. Thanks of it we will not be lost in which one request is good an which one is being tested. We can mark the good one with green and the tested one with red color. Request marking is also available in context menu under Mark option. Red color has an additional keyboard shortcut – insert key.

Short animation showing how to compare HTTP requests in Fiddler:

Animation - HTTP request comparing with Fiddler and WinMerge

Animation – HTTP request comparing with Fiddler and WinMerge

As you can see at the animation above there is major problem with request comparing in WinMerge. When request’s body is a string of parameters placed in one line then you will know that this line is changed but you will not know where exactly. Solution for this problem will be presented in the next post (Custom WinMerge plugin).

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