Add enum support

[redox]

Motivation and Context

This adds support for enum on string property.

How Has This Been Tested?

Before	After

Breaking Changes

None

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation update

Checklist

• I have read the MCP Documentation
• My code follows the repository's style guidelines
• New and existing tests pass locally
• I have added appropriate error handling
• I have added or updated documentation as needed

Additional context

[seuros]

Can you point out where do you see this in the specification.

[redox]

Can you point out where do you see this in the specification.

I linked https://json-schema.org/understanding-json-schema/reference/enum in the description, this is what you were looking for right?

[seuros]

I understand that the JSON schema supports enums, and I use it in OpenAPI.

However, my question was about this specification.

While the idea of using enums is great, I believe it should be an official part of the specification to ensure compatibility across different clients and servers.

If a client is strict about adhering to the specification, it could reject any request/response from a server that doesn’t conform as malformed or invalid.

I don’t intend to push back, but I think this is something worth discussing in the GitHub discussion to get community input.

From there, we (the community) can consider implementing it experimentally in both client and server capabilities.

[redox]

Oh I see. The current specification is indeed vague about it (the TS version simply rely on object here). I might have wrongly assumed that the inputSchema would support the whole JSON Schema as it's documentation is A JSON Schema object defining the expected parameters for the tool..

I'll start a discussion in https://github.com/modelcontextprotocol/specification

[redox]

For the record: modelcontextprotocol/specification#210

[seuros]

Just for info, when a client wants to get the data for that field, it emit a completion request for tools and resources.

So your goal is doable if your server return the correct enum.

One thing that bother me is that it keep emitting it while you are typing.