You can create your own debugging commands by writing an extension DLL. For example, you might want to write a command to display a complex data structure, or a command that will stop and start the target depending on the value of certain variables or memory locations.
There are two different types of debugger extensions:
DbgEng extensions. These are based on the prototypes in the dbgeng.h header file, and also those in the wdbgexts.h header file.
WdbgExts extensions. These are based on the prototypes in the wdbgexts.h header file alone.