Through my experience, I have utilized a variety of prominent tools such as fiddler, firebug, httpfox, and live http headers. In my opinion, the most effective tool is HTTPFox, especially if you are using Firefox. HTTPFox offers simple filtering capabilities, allows for viewing JSON requests/responses in raw or formatted form, and presents a clean interface.
I also rely heavily on WFetch when testing web services and AJAX functionalities. Typically, I extract the request from HTTPFox and insert it into WFetch for seamless testing without having to go through the browser every time. With WFetch, I can easily replay the request by hitting F5 and directly modify the request.
On a side note, it's important to pay attention to content-length in WFetch, especially when dealing with POST payloads. If modifications are made to the payload, ensure that the content-length is adjusted accordingly. To manage this effectively, I save my requests in a file and specify the file path in WFetch. This way, the length of the line in the file helps determine the appropriate content-length.
https://i.sstatic.net/HFhf3.png
(source: koreus.com)
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