Is that because they're parsing porcelain output? Or is git's plumbing machine-readable but not well specified?

But git users are more familiar with porcelain so I wouldn't be surprised if they parsed that for an initial implementation.

It sounds like plumbing shouldn't break as often as you imply:

> The interface (input, output, set of options and the semantics) to these low-level commands are meant to be a lot more stable than Porcelain level commands, because these commands are primarily for scripted use.

https://schacon.github.io/git/git.html#_low_level_commands_p...

However, doesn't seem like they're nearly as rigorous as you hope.