What YAML Is

YAML ("YAML Ain't Markup Language", originally "Yet Another Markup Language") is a human-readable data format. Most associated with configuration files.

Key uses:

• k8s manifests: pods, deployments, services.
• CI/CD: GitHub Actions, GitLab CI, CircleCI.
• Helm charts: Kubernetes templates.
• Ansible playbooks: config management.
• docker-compose: multi-container apps.
• Application configs: many web frameworks.

Why YAML over JSON?

• Human-friendly: less punctuation, indent-based.
• Comments: native (JSON has none).
• Multi-line strings: easy.
• References: anchors + aliases (DRY).
• Document streams: multiple docs per file.

Why JSON over YAML?

• Stricter: no ambiguity (Norway problem, octal).
• Faster: JSON parsers are simpler.
• Mandatory keys quoted: less error-prone.

YAML 1.2 (2009): sub-superset of JSON. Most YAML parsers can parse JSON.

Example:

name: Alice
age: 30
emails:
  - [email protected]
  - [email protected]
address:
  street: 123 Main St
  city: Wonderland

vs JSON:

{
  "name": "Alice",
  "age": 30,
  "emails": ["[email protected]", "[email protected]"],
  "address": {
    "street": "123 Main St",
    "city": "Wonderland"
  }
}

Real implementations:

• PyYAML (Python): mature, slow.
• ruamel.yaml (Python): preserves comments, faster.
• go-yaml: Go's standard.
• js-yaml: JS.
• snakeyaml: Java.
• libyaml: C (reference).

We'll build a parser for a YAML subset (no anchors/tags/folded strings; cover the basics).

Reference: yaml.org spec.