yml

YML refers to a file extension commonly used for YAML, a human-readable data serialization language. YAML stands for "YAML Ain't Markup Language" and is widely used for configuration files and data exchange between programs. The yml extension is paired with yaml, and both denote the same underlying format.

YAML emphasizes readability and uses indentation to indicate structure. Data is expressed as mappings (key: value), sequences (lists prefixed by dashes), and scalars (strings, numbers, booleans). It supports nested structures, comments (starting with #), and more advanced features such as anchors and aliases for reusing content. While YAML is designed to be easy for humans to read, it remains a strict format: indentation level and syntax must be consistent to avoid parsing errors.

YAML itself is a standard with YAML 1.2 being the current widely adopted version. It is designed to be compatible with JSON; any JSON document is also a valid YAML document, though YAML offers more expressive syntax. Both .yaml and .yml are commonly used as file extensions for YAML documents.

Common uses for YAML include configuration files, data exchange between applications, and declarative tooling. It is a staple in many ecosystems: Docker Compose files, Kubernetes manifests, and GitHub Actions workflows frequently use .yml or .yaml extensions. Its readability makes it a preferred choice for complex configurations that benefit from clear, structured data representation.

Security and tooling considerations are important when parsing YAML. Some parsers may execute arbitrary code if loaded unsafely, so many languages recommend safe loading methods and validated schemas. A wide range of libraries exists across languages to read and write YAML content.