How YAML maps to JSON

Mappings become objects, sequences become arrays, and scalars become strings, numbers, booleans or null.
Values are read with the YAML 1.2 rules used by modern tools: true/false are booleans, but yes, no, on and off stay strings (in YAML 1.1 they were booleans — the cause of the well-known "Norway problem", where the country code NO became false). Dates such as 2024-03-01 are kept as strings.
Anchors and aliases are expanded, including merge keys (<<: *base), so the JSON contains the full values.
A file with several documents separated by --- becomes a JSON array with one element per document.
Comments are dropped, because JSON has no comments.

Common YAML errors

Tabs for indentation — YAML only allows spaces.
Inconsistent indentation — every item of a list or mapping must line up.
A colon inside an unquoted value — title: Note: read me needs quotes: title: "Note: read me".
Duplicate keys in the same mapping are rejected rather than silently overwritten.

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