[zaarn]

JSON does have Schemas and Validation (JSON-LD and RDF I believe are the relevant standards here), which are backwards compatible with parsers that don't support it (though the number of parsers that do is sadly rather low).

In principle you still get schema and validation.

[majewsky]

Also https://swagger.io/

[tannhaeuser]

No. JSON-LD aims at aiding interpretation of JSON as RDF data (semantic web, description logic). It's terrible IMHO.

[zaarn]

There is also JSON-schema.org if you don't like RDF/LD.