YAML

YAML (YAML Ain't Markup Language, originally Yet Another Markup Language) is a human-friendly data serialization standard designed to work seamlessly with modern programming languages for configuration files, data exchange between processes, and application messaging. Originally proposed by Clark Evans in 2001 and developed collaboratively with Ingy dot Net and Oren Ben-Kiki, YAML was created to combine the simplicity of XML with the readability of plain text, addressing the verbosity of XML and the complexity of SGML-based formats. The current specification is YAML 1.2 (published 2009, with YAML 1.2.2 released in 2022 as a revision), which is a superset of JSON, meaning any valid JSON document is also a valid YAML document. YAML supports core data types including scalars (strings, integers, floating-point numbers, booleans, null), sequences (lists/arrays), and mappings (dictionaries/objects), with advanced features like anchors and aliases for reference reuse, merge keys for inheriting mapping content, complex keys, tags for custom types, flow style (JSON-like inline syntax) and block style (indentation-based), multi-line strings with literal and folded styles, and comments using the hash symbol. YAML is ubiquitous in modern software infrastructure: Kubernetes manifests are written in YAML, Docker Compose uses YAML, GitHub Actions and GitLab CI/CD pipelines use YAML, Ansible playbooks use YAML, CI/CD configurations across platforms, Helm charts, OpenAPI specifications, and cloudformation templates all use YAML. Major YAML libraries include PyYAML and ruamel.yaml for Python, js-yaml for JavaScript, go-yaml for Go, serde_yaml for Rust, and SnakeYAML for Java.