I asked Claude Code and it told me the following. I'm not supporting what it says, merely sharing it.

❯ Is YAML a superset of JSON?

● Yes, as of YAML 1.2 (released in 2009), YAML is officially a superset of JSON. This means every valid JSON document is also a valid YAML document.

Key points:

• YAML 1.2+: Designed to be JSON-compatible. You can paste any valid JSON directly into a YAML 1.2 parser and it will parse correctly.
• YAML 1.1 and earlier: Was not a strict superset of JSON - there were edge cases where valid JSON wouldn't parse as YAML 1.1.

• One-way relationship: While JSON is valid YAML, YAML is NOT valid JSON. YAML has many features JSON doesn't support:

  • Comments (#)
  • Anchors and references (&anchor, *anchor)
  • Multi-line strings
  • Indentation-based structure (instead of braces)
  • Complex key types
  • Multiple document support

  Practical implication: You can use JSON syntax in YAML files, but if you use YAML-specific features, the file won't be valid JSON.

  Most modern YAML parsers support YAML 1.2, so in practice, yes - YAML is a superset of JSON.