Enable structured inputs/outputs for Resources · Issue #956 · modelcontextprotocol/modelcontextprotocol · GitHub
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Enable structured inputs/outputs for Resources #956

Description

@simba-git

Is your feature request related to a problem? Please describe.
Many companies, including our own, have existing APIs that they wrap with MCP servers. Those APIs have clearly defined inputs and often have a structured output, typically JSON or similar.

Most projects just use Tools directly even when data retrieval should actually be structured as Resources in MCP (GET Requests are about equivalent to Resources in my reading of the spec). Tools are supposed to be for "executable functionality to clients" not data retrieval.

The problem with Resources is that they dont allow for structured inputs, we have to try to get the client to create a structured Resource URI which isn't feasible for any even mildly complex schema. And not having structured outputs makes Resources less powerful then tools.

For these reasons, almost everyone wrapping APIs that I've talked to just do a mapping of API calls to Tools.

Describe the solution you'd like
I would like Resources to also be able to have structured inputs and outputs along with the resource URI.

Describe alternatives you've considered
We just use tools for both "resources" and tools.

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