[Gazler]

A git hook would certainly work for this as you described and I would certainly encourage people to investigate that route if it is appropriate for them. http://git-scm.com/book/en/v2/Customizing-Git-Git-Hooks

The goal for GitCop is to be fast and easy to set up in a way that integrates well into a GitHub pull request based flow.

[rurounijones]

By that point isn't it too late? Or do you expect people to commit --amend and force push?

[Gazler]

It is common in many flows to expect people to do a force push if something is wrong with their pull request, e.g. having 15 commits that look like:

    Try stuff
    Another prototype
    Fix something
    ...
    Revert prototype

It is fairly common (in my experience) for the contributor to be asked to squash those commits.

In my opinion, the more guards in place the better.

[dmethvin]

I think that's a key point, the earlier you can catch the problem the less frustrating for both sides. There is https://www.npmjs.org/package/commitplease for commit hooks but it's still handy to have something audit pull requests.