$schema key

A reserved key a document can put in its own metadata, to name the schema or schemas it should be validated against.

It takes a single reference or a list. Because it’s a manni meta directive rather than real metadata, $schema is stripped before validation, so a schema with additionalProperties: false won’t flag it. In the precedence chain it sits above config but below a --schema flag. A schema carries a different value under the same key, its meta-schema URI. See The $schema key in a file.