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Reconsider ambiguous implementation note regarding missing inputSchema in MCP headers #2974

Description

@pcarleton

What's broken?

The spec is ambiguous or self-contradictory

Where in the spec or docs?

https://modelcontextprotocol.io/specification/draft/basic/transports/streamable-http#custom-headers-from-tool-parameters

What should happen?

We should evaluate removing the current implementation note regarding the handling of mcp-param headers when the inputSchema is not available. (the one edited in #2972)

The current language suggests a scenario where a client might make a tool call without having retrieved the inputSchema, which is unclear and likely represents an invalid state that shouldn't be explicitly handled in this manner. It is generally expected that clients will have fetched the tools/list information prior to executing calls.

Proposed Action:

Delete the implementation note regarding the inputSchema condition entirely.

Although we need to make sure we do explain that if you get rejected, you should tools/list to get the schema for custom header info, and then retry.

What actually happens?

...

Anything else?

No response

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