JSON

A JSON document looks like {"name": "Ada", "age": 36, "tags": ["admin"], "active": true}. It has only a handful of value types: strings, numbers, true and false, null, arrays (lists) and objects (name-value pairs). The syntax comes from JavaScript, but every mainstream language can parse it, which is why it replaced XML as the default format for web APIs.

Its simplicity has limits. There are no comments and no dates (they travel as text such as '2026-09-29T10:00:00Z'), binary data has to be encoded, and a single trailing comma makes a file invalid. Very large numbers lose precision in JavaScript, which is why IDs are often sent as strings. JSON Schema describes the shape a document should have, and databases such as PostgreSQL (JSONB) and MongoDB store it natively.