Reply tool calls with structuredContent

[hstaudacher]

The MCP spec has added a structuredContent field in https://modelcontextprotocol.io/specification/2025-06-18/server/tools#structured-content.

The tool call results should populate that field.

[SamMorrowDrums]

Hey @hstaudacher this is indeed an interesting area, the reason we held back at the time when this was announced was because there is a token cost to providing the output schemas and it also makes them more brittle so there is a significant maintenance cost too. I also wasn't clear reading the specification for it what that means for error responses.

I think it's worth revisiting this and deciding if the benefits outweigh the costs etc. but as mentioned, these schemas don't come for free token wise, and we've already had enough issues with too many tokens, so to decide to introduce this would be a significant decision I think, and I'd also be interested in whether there are specific tools that would benefit more than others. Fortunately models have thus far been very familiar without our API outputs, and so in practice I also haven't experienced problems that this is intended to solve AFAICT.

What are you thinking?