In Mac OS X Mountain Lion 10.8.4 and later, Apple provides the Wireless Diagnostics tool. It’s more than just a stumbler; it can help you detect and fix Wi-Fi issues as well. Best of all, it’s a native tool included with the OS. To get started, press the Option key and then click the Airport/Wi-Fi icon. This displays more details on your current Wi-Fi connection while also making the Wireless Diagnostics shortcut available. When you open Wireless Diagnostics, it will begin running tests to detect any issues. Otherwise you can choose Window > Utilities to access the other wireless tools. You can see the current connection and environment details, perform frame captures, configure logging, scan for network details, and view performance info, including noise and SNR values. For more info, Apple provides a great tour and tutorial on Wireless Diagnostics.