Tool output schema doesn't support basic types

[asklar]

https://github.com/modelcontextprotocol/csharp-sdk/blame/b90f17bccb5f5f781318bc5b22e0d94205d67857/src/ModelContextProtocol.Core/McpJsonUtilities.cs#L65

Looks like this mandates output must be an object; however, in the spec AFAICT, the output could be any basic type like string, number, etc.

Ask is to relax this to support at least string + numeric types

[eiriktsarpalis]

however, in the spec AFAICT, the output could be any basic type like string, number, etc.

Looking at the specification, this does not appear to be the case:

https://github.com/modelcontextprotocol/modelcontextprotocol/blob/0f0b48d9f3aea7ff2bdfb1a282e678c0a6249c80/schema/2025-06-18/schema.json#L2417-L2420

[stephentoub]

The same shows up here:
https://github.com/modelcontextprotocol/modelcontextprotocol/blob/0f0b48d9f3aea7ff2bdfb1a282e678c0a6249c80/schema/draft/schema.ts#L1056-L1064

There was also discussion of this on the TypeScript SDK, where it was closed as by design unless/until the core spec changes:
modelcontextprotocol/typescript-sdk#685

[asklar]

yep you are correct, I misinterpreted the spec, sorry :)