YAML (YAML Ain't Markup Language) is a human-readable data serialization format widely used for configuration files. It's the default format for Docker Compose, Kubernetes manifests, GitHub Actions workflows, Ansible playbooks, and many other DevOps tools. Unlike JSON, YAML supports comments and is designed to be written and read by humans.

YAML vs JSON vs XML

YAML is the most human-readable — great for config files edited by hand
JSON is strict and widely supported — great for APIs and data interchange
XML is verbose but supports schemas and namespaces — great for enterprise systems
YAML is a superset of JSON — valid JSON is also valid YAML

Frequently Asked Questions

YAML uses spaces (never tabs) for indentation, and indentation levels must be consistent. The most common error is mixing tabs and spaces. Set your editor to insert spaces and use 2 spaces per indent level for YAML files.

Most strings don't need quotes. However, you should quote values that start with special characters like :, #, @, !, >, |, or values that look like numbers (123) or booleans (true, false, yes, no) but should be treated as strings.

In YAML, a colon must be followed by a space to be treated as a key-value separator. A colon without a space (like in a URL https://...) is treated as part of the string, not a key-value pair.