Add Elicitation Support for MCP Client Information Requests

[naji247]

Overview

Add support for tracking MCP elicitation events, which allow servers to request additional information from users through the client during interactions. MCPcat should capture when elicitation requests happen and how users respond to them.

Background

The MCP elicitation specification (spec) provides a standardized method for servers to dynamically gather necessary information from users. This includes:

• Simple text requests for basic string input
• Structured data requests with JSON schema validation
• Three response actions: accept (user submits data), decline (explicit rejection), and cancel (dismissal without choice)

Implementation Requirements

1. Event Type Support

Add new event types to track elicitation interactions:

• MCP_ELICITATION_CREATE - When a server requests information from the user
• MCP_ELICITATION_RESPONSE - When the user responds with accept/decline/cancel

2. Request Interception

Extend the existing request handler system in modules/overrides/mcp_server.py to intercept:

• elicitation/create requests from servers
• Response messages from clients

3. Event Tracking

Capture the following data for elicitation events:

• Request events: Message displayed to user, requested schema, validation rules
• Response events: User action (accept/decline/cancel), submitted data (if accepted)

4. Data Structure

Events should leverage existing UnredactedEvent fields:

• event_type: New elicitation event types
• parameters: Request schema and message
• response: User's response action and data
• user_intent: Could store the elicitation message for context

Technical Approach

1. Add EventType enum values in src/mcpcat/types.py:

MCP_ELICITATION_CREATE = "mcp:elicitation/create"
MCP_ELICITATION_RESPONSE = "mcp:elicitation/response"

2. Create wrapper handlers in src/mcpcat/modules/overrides/mcp_server.py:

async def wrapped_elicitation_create_handler(request: ElicitationCreateRequest) -> ServerResult:
    # Track the elicitation request
    # Store schema, message, and context
    # Forward to original handler
    # Track the response

3. Handle forward compatibility: Since elicitation may not be in the current Python MCP SDK version, we should:
   • Check for elicitation request types dynamically
   • Create temporary type definitions if needed
   • Gracefully handle missing elicitation support

Acceptance Criteria

• MCPcat tracks when servers request information via elicitation
• User responses (accept/decline/cancel) are captured with appropriate context
• Submitted data from accepted elicitations is recorded
• Implementation is forward-compatible with future MCP SDK updates
• Events are properly sent to MCPcat API or telemetry exporters

Notes

• The Python MCP SDK may not yet include elicitation support, so implementation should be designed to activate when the SDK adds these capabilities
• Consider privacy implications when tracking user-submitted data in elicitations
• Ensure redaction functions work properly with elicitation response data