Add structuredContent responses

[macbookandrew]

This adds the ability for MCP tools to return a structuredContent key/value object as defined in the spec.

This will be useful for building ChatGPT Apps and passing tool responses to the app UI:

• https://developers.openai.com/apps-sdk/reference/#tool-results
• https://developers.openai.com/apps-sdk/build/mcp-server/

[grachov]

@macbookandrew This is a really nice feature - I was actually thinking about implementing something similar myself, but you beat me to it 😄
According to the specification, the content text should match the same JSON that’s sent in the structuredContent field: https://modelcontextprotocol.io/specification/draft/server/tools#structured-content.
It would also be great to include an outputSchema property for better alignment with the spec and to make the output more consistent.

@nunomaduro Were you considering using a different library for JSON Schema? The current one seems a bit limited - for example, it doesn’t support all properties defined in the spec.

[macbookandrew]

According to the specification, the content text should match the same JSON that’s sent in the structuredContent field: https://modelcontextprotocol.io/specification/draft/server/tools#structured-content.

Hmm...good point. So maybe instead of ->withStructuredContent() it makes more sense to add a new Response::structured(...) instead?

[grachov]

Yes, or even a separate response class to build and validate CallTool response easier.

[davidhole]

Looks really great! I think your suggestion @macbookandrew of Response::structured(...) seems like a really good approach.

I guess we'd also need to define the output schema as we do the input schema as per the spec also?

And then a few JSON assertions on the test response and it'd be perfect.

Let me know if you like me to contribute!

[macbookandrew]

Thanks for your input guys! I'm not sure we need the output schema so haven't added it yet, but this now uses Response::structured(...) and I'm going to start testing this branch in a work project tomorrow to get a feel for real-world use.

Any thoughts on this so far? Anybody want to add the output schema?

[wpalani]

Working on a project now and this fit exactly what i need.