.yml File — YAML File

YML is an alternative file extension for YAML (YAML Ain't Markup Language) files. Both .yml and .yaml extensions represent identical content and are processed by the same parsers. The .yml extension became popular because of the historical three-character extension convention, though the official YAML specification recommends .yaml. Usage conventions vary by ecosystem: Docker Compose traditionally uses docker-compose.yml, GitHub Actions uses .yml for workflow files, and many Ruby projects (Rails, Jekyll) prefer .yml for configuration. Convention is largely a matter of project and community preference rather than technical necessity. Some projects enforce consistency through linting rules or contributing guidelines. All YAML parsers, editors, and tools treat both extensions identically, applying the same syntax highlighting, validation, and processing. When starting new projects, either extension is acceptable, but maintaining consistency within a project is recommended. The .yml extension is slightly more common in practice according to GitHub statistics, particularly in the JavaScript, Ruby, and DevOps ecosystems.