YAML is a human-readable config format that's a strict superset of JSON. Used by Docker Compose, Kubernetes manifests, GitHub Actions workflows, Ansible playbooks, OpenAPI/Swagger specs, and CircleCI configs. Indentation matters, which trips up users accustomed to brace-based configs. Spec versions: 1.1 (2005, Ruby/Python ecosystems) and 1.2 (2009, current). Most tools default to a 1.1/1.2 hybrid.
How to open
Any text editor. VS Code, IntelliJ, and most modern IDEs ship YAML syntax highlighting and validation. The `yamllint` CLI catches indentation bugs before they reach CI.