New MCP specification version 2025-06-18

[klapaudius]

Summary

The Model Context Protocol has released a new specification version (2025-06-18) with significant changes that need to be implemented in the symfony-mcp-server bundle. This feature request outlines the necessary updates to ensure compliance with the latest specification.

Motivation

Keeping the symfony-mcp-server bundle up-to-date with the latest MCP specification ensures:

• Compatibility with modern LLM clients
• Access to new features like structured tool output and elicitation
• Better user experience with metadata enhancements

Specification Changes Overview

The new specification (2025-06-18) introduces several breaking changes and new features as detailed in the official changelog.

Required Implementation Tasks

1. Breaking Changes

Remove JSON-RPC Batching Support

• Current: Bundle may support batch requests
• Required: Remove any batch request handling capabilities
• Impact: Simplifies request processing but may affect clients using batching
• Related issue: HTTP Streamable must return JsonResponse for single requests #39

Structured Tool Output

• Required: Support for structured output from tools
• Tasks:
  • Update BaseToolInterface to support structured data Output
  • Modify tool list response serialization
• Related issue: Implements Structured Tool Output from MCP specification version 2025-06-18 #48

2. New Protocol Features

Elicitation Mechanism

• Required: Implement server-initiated user information requests
• Tasks:
  • Create new elicitation request/response handlers
  • Add elicitation support to MCPProtocol
  • Implement elicitation flow in transport layers

Enhanced Resources output

• Required: Adapt resources and resource templates json output
• Tasks:
  • Add name and title to resource's output
  • Add name and title to resource template's output
• Related issue: add name and title in returned json on resource/call #49

🚧 To be continued 🚧