JSON-LD

JSON-LD (JavaScript Object Notation for Linking Data) is a W3C standard for expressing linked data as ordinary JSON. It adds a lightweight semantic layer on top of the JSON teams already ship: a @context maps human-friendly keys to globally unique identifiers (IRIs), so a machine can know that last means a last trade rather than a last quote. The result is JSON that carries meaning, not just shape.

• @context for meaning - Maps local property names to shared vocabularies and IRIs, turning ambiguous keys into globally understood terms.
• @id and @type - Give every node a stable identity and a class, so records can be linked and reasoned about across systems.
• Graph constructs - @graph and node references let a document describe a web of connected entities instead of one flat object.
• Backward-compatible with JSON - A JSON-LD document is still valid JSON, so existing parsers keep working while semantics ride along for the tools that care.

In real API operations JSON-LD is the semantic layer most producers skip — and the one agents most need. It powers schema.org markup, hypermedia patterns alongside formats like HAL, and self-describing payloads that let a client resolve what a field means without a human reading the docs. As the agentic turn puts machine clients in charge of interpreting responses, mapping JSON Schema shapes to shared meaning through JSON-LD is what keeps an agent from calling the wrong operation on data it only half understands.