I know I've seen some people recommend 50 (my guess is that's to make some room for metadata from commands like `git log --online` in an 80-column terminal?) but I've personally always capped all lines at 72, including the first. 100 seems like a reasonable limit too, but I probably wouldn't go above that.

> git says they're all illegal by some margin

Git will accept almost anything as a commit message. Is there a specific style guide you're referring to?

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EDIT: Huh, I guess git does have an official recommendation. I'd never noticed this text in `git help commit`:

> Though not required, it's a good idea to begin the commit message with a single short (less than 50 character) line summarizing the change, followed by a blank line and then a more thorough description.

I wouldn't feel bad about not following this advice. Even the author doesn't seem dogmatic about it.