People often want to write programs that call monotone — for example, to create a graphical interface to monotone's functionality, or to automate some task. For most programs, if you want to do this sort of thing, you just call the command line interface, and do some sort of parsing of the output. Monotone's output, however, is designed for humans: it's localized, it tries to prompt the user with helpful information depending on their request, if it detects that something unusual is happening it may give different output in an attempt to make this clear to the user, and so on. As a result, it is not particularly suitable for programs to parse.
Rather than trying to design output to work for both humans and computers, and serving neither audience well, we elected to create a separate interface to make programmatically extracting information from monotone easier. The command line interface has a command automate; this command has subcommands that print various sorts of information on standard output, in simple, consistent, and easily parseable form.
For details of this interface, see Automation.