How to contribute

We'd love to accept your patches and contributions to this project. There are just a few small guidelines you need to follow.

Contributor License Agreement

Contributions to this project must be accompanied by a Contributor License Agreement (CLA). You (or your employer) retain the copyright to your contribution; this simply gives us permission to use and redistribute your contributions as part of the project. Head over to to see your current agreements on file or to sign a new one.

You generally only need to submit a CLA once, so if you‘ve already submitted one (even if it was for a different project), you probably don’t need to do it again.

Checking out source

Set up git

If you haven't already, configure your git user email and name:

git config --global "<your-email>"
git config --global "Your Name"


With your git configured, you can now checkout the source with:

git clone && (cd tools && f=`git rev-parse --git-dir`/hooks/commit-msg ; mkdir -p $(dirname $f) ; curl -Lo $f ; chmod +x $f)

The last command not only clones the repository but also adds a git pre-commit hook that will be explained below in “Making changes”.

Making changes

The typical git workflow applies here. You can use git checkout -b to create a branch and git commit to commit local changes. The pre-commit hook that was downloaded earlier will insert a Gerrit (Gerrit is explained below) Change-Id into every local commit you make. This Change-Id is specific to Gerrit and defines a change: one change and the corresponding review in Gerrit will have one Change-Id. If a Change-Id is not provided in the commit message, Gerrit will reject the commit. While you can manually add a Change-Id later, it's strongly recommended you include it from the start, when you clone the repository.

Code reviews

All submissions, including submissions by project members, require review. We use Gerrit for this purpose.

Register with Gerrit

Before you can request code reviews, you need to register with Gerrit first. You can do that by going to and clicking “Sign in” at the top right corner.

Set up git cookies

You will also need to generate and configure your git cookies in order to push changes to Gerrit. The following steps help you with that:

  1. Go to

  2. Log in with your google account

  3. Follow the on-screen directions page to set up/append to your ~/.gitcookies file

  4. Verify that your cookies are correctly setup:

    git ls-remote

Upload a CL

git push origin HEAD:refs/for/master

The command will print a URL to the CL that has just been uploaded. You can follow the URL to the Gerrit UI and add reviewers from there.

Community guidelines

This project follows Google's Open Source Community Guidelines.