I've been looking for something easier to use than Ethereal when debugging HTTP server requests and HTTP Scoop seems to fit the bill. It works right out of the box (for example, it correctly chose the en1 interface on my Airport connected laptop rather than making me figure that out) and it automatically captures and decodes HTTP traffic as advertised. It shows as much detail about each request as anyone could wish for from the complete headers down to the TCP/IP protocol exchange. There are some user interface oddities but polish is a lot easier to add than basic functionality which the app already has.

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