Structured content (MCP)
Structured content is an optional field, structuredContent, a Model Context Protocol tool can return in its call result alongside -- not instead of -- the usual content array of text, image or resource blocks, carrying the result as a plain JSON object rather than text a client has to parse back out itself. A tool definition can declare an outputSchema, a JSON Schema describing the shape that result is expected to take; when it does, the server MUST return structured content conforming to it, and a client SHOULD validate the response against that schema before trusting it. For backwards compatibility, a tool returning structured content should still serialize the same JSON into a text block too, so an older client that only understands unstructured content doesn't break. The specification notes this is unrelated to LLM "structured outputs" (schema-constrained model generation).
By AdminKit team, Netbase JSC · Updated