What’s the difference between .yaml and .yml?

Both .yaml and .yml file extensions refer to files containing YAML (YAML Ain't Markmarkup Language), a human-readable data serialization format. These extensions represent the same YAML standard; there is no technical difference between them. The distinction lies purely in the naming convention preference. .yaml is the official and formally recommended extension defined by the original YAML specification. .yml emerged later as a shorter, convenient alternative widely adopted due to historical filename limitations favoring three-letter extensions.

In practice, both extensions function identically. Software tools like Kubernetes configuration files (.yaml), Ansible playbooks (.yml), and Docker Compose files (.docker-compose.yml) utilize either extension interchangeably. Developers often choose .yml for simplicity when saving files manually, while frameworks might default to .yaml. Major platforms including Azure DevOps, GitHub Actions, and AWS CloudFormation accept both without distinction.

The coexistence of two extensions causes minimal technical conflict, as parsers recognize the content regardless of the suffix. However, it can lead to minor confusion for users regarding consistency. The key advantage is flexibility: developers can choose either. The recommended practice is consistency within a project or organization, using .yaml where possible to align with the formal specification. Future tooling will continue to support both extensions equally.