WLANs are constantly undergoing extensive research and development, and scientists keep coming up with new methods to improve existing protocols and amend standards. Experimental assessment has been an important part of 802.11 research, however measuring the detailed behaviour of the medium and hardware has been challenging. In this paper we design a diagnostic tool, WiFo, for IEEE 802.11-based WLANs. This tool helps developers and researchers monitor and analyze the wireless signals and details such as backoff distribution in a user-friendly environment. Our solution is much cheaper and easier to use than existing tools, and provides more flexibility by allowing users to add functionality. We then use WiFo to study several aspects of some off-the-shelf hardware and their corresponding software drivers, and show some interesting results regarding how they apply standard specifications.