David Kimura PRO said almost 6 years ago on Using GitLab Runner for CI/CD :
You can check the docs for additional tags https://docs.gitlab.com/ce/ci/yaml/README.html#validate-the-gitlab-ciyml Which also includes a validator at /ci/lint. Alternatively, you can make a post request to the ApI https://docs.gitlab.com/ee/api/lint.html