YAML tools

YAML is the config language behind Kubernetes manifests, GitHub Actions and GitLab CI workflows, Docker Compose files and Ansible playbooks. Its indentation-based syntax is easy to read and easy to break. One misaligned space changes which mapping a key belongs to, and tabs are not allowed for indentation at all.

Most YAML surprises come from implicit typing. Under the older YAML 1.1 rules, unquoted values such as yes, no, on and off are booleans, so a country code like NO can become false. YAML 1.2 narrowed the core schema to true and false. Many parsers still default to 1.1 behavior, so quoting ambiguous values is still good practice. Anchors (&) and aliases (*) let one document reuse a block, and a single file can hold several documents separated by ---.

The tools below cover the usual YAML jobs. Format and lint a file before you commit it. Compare two versions by value instead of by line, deep-merge a base file with environment overrides, and query nested values with JMESPath or JSONPath. When YAML has to talk to something else, convert it to JSON, TOML or .env variables, or run a Kubernetes manifest through a structural check. Everything runs in your browser, so internal config and secrets stay on your machine.