The local environment is a great place to iterate on a CircleCI configuration. You'll catch errors faster than pushing to CI, and help drive a fast, iterative configuration process.
Install the CircleCI CLI via Homebrew (or any package manager of your choice):
$ brew install circleci
Then, in the same directory as your .circleci/config.yml, run:
$ circleci config validate
# Config file at .circleci/config.yml is valid