Support 2025-06-18 Spec

[ajevans99]

Added/Changed

• Add support for structured tool output (PR #371)
• Add support for elicitation, enabling servers to request additional information from users during interactions. (PR #382) Requires server to client implementation, types only for now
• Add support for resource links in tool call results. (PR #603)
• Add _meta field to additional interface types (PR #710), and specify proper usage. Also adds extraFields to allow [key: string]: unknown; on __Result types align with interfaces/schema https://modelcontextprotocol.io/specification/2025-06-18/schema_
• Add title field for human-friendly display names, so that name can be used as a programmatic identifier (PR #663)

Not Handled

• Remove support for JSON-RPC batching (PR #416)
• Require negotiated protocol version to be specified via MCP-Protocol-Version header in subsequent requests when using HTTP (PR #548).
• Add context field to CompletionRequest, providing for completion requests to include previously-resolved variables (PR #598).

Motivation and Context

Support many changes in recent MCP spec update.
https://modelcontextprotocol.io/specification/2025-06-18/changelog

How Has This Been Tested?

• New unit tests
• MCP Inspector npx @modelcontextprotocol/inspector@latest

Breaking Changes

• New case on public enum Tool.Content.resourceLink
• Updated associated values on enum case Tool.Content.resource to include optional title and annoations properties

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

_meta is not a Swifty name but does map nicely to the spec. Open to suggestions

[alainakafkes]

hi there and thank you for taking a stab at supporting the latest MCP spec! i saw this PR because i am hoping to use Result's structuredOutput for a project. i have no special role in this repo but wanted to offer some feedback to help build interest in this work

[ajevans99]

hi there and thank you for taking a stab at supporting the latest MCP spec! i saw this PR because i am hoping to use Result's structuredOutput for a project. i have no special role in this repo but wanted to offer some feedback to help build interest in this work

Thanks for the early review. Implemented a bunch of your suggestions and re-thought the meta and general fields.

[aehlke]

I see you had some changes last week. Is this ready to use as a fork until it gets reviewed? I hope this will be merged if it is ready. Thanks!

[ajevans99]

I see you had some changes last week. Is this ready to use as a fork until it gets reviewed? I hope this will be merged if it is ready. Thanks!

Ready on my side. @mattt could we get a review when you get a chance