By placing the Bluefruit LE module in 'Command' mode (set the mode selection switch to CMD or setting the MODE pin to a high voltage) you can enter a variety of Hayes AT style commands to configure the device or retrieve basic information about the module of BLE connection.
You can determine if you are in Command Mode by looking at the mode LED. It should blink three times followed by a three second pause, as shown below:
When operating in command mode, the Bluefruit LE Pro modules use a Hayes AT-style command set to configure the device.
The advantage of an AT style command set is that it's easy to use in machine to machine communication, while still being somewhat user friendly for humans.
We have a huge amount of commands and details on how to use them, so please do check out our list of possible commands over on the Bluefruit LE page (no need to duplicate all of the content here!)