MCP Elicitation Not Working at Runtime - FastMCP Remote Server Issue

[Pratikkumar24]

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• Server Implementation
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Your Question

MCP Elicitation Not Working at Runtime - FastMCP Remote Server Issue

Problem Summary

MCP elicitation is "not working at runtime" when calling tools on a remote FastMCP server deployed on fastmcp.cloud. The elicitation form never appears, and the tool execution hangs or fails silently.

What works:

• ✅ Elicitation works perfectly with local stdio transport (Cursor)
• ✅ Elicitation works perfectly with MCP Inspector using HTTP/remote
• ✅ Server code is correct (proven by MCP Inspector working)

What doesn't work:

• ❌ Elicitation hangs/doesn't appear when calling tools via Cursor with remote SSE/http transport
• ❌ Elicitation doesn't appear at runtime in the fastmcp.cloud UI when executing tools

Technical Details

Server Setup

• Framework: FastMCP (Python)
• Transport: SSE (Server-Sent Events) for remote deployment
• Deployment: fastmcp.cloud
• Server Code Example:

from fastmcp import FastMCP, Context
from dataclasses import dataclass

mcp = FastMCP(name="elicitation-server")

@dataclass
class UserData:
    name: str
    age: int
    email: str = ""

@mcp.tool
async def collectUserData(ctx: Context) -> str:
    """Collect user data through MCP elicitation."""
    logger.info("collectUserData: Starting elicitation request")
    
    result = await ctx.elicit(
        message="Please provide your personal information (name, age, and optionally email).",
        response_type=UserData
    )
    
    if result.action == "accept":
        user = result.data
        return f"Thank you {user.name}! You are {user.age} years old."
    # ... handle decline/cancel

Client Configuration

Cursor MCP Config (.vscode/mcp.json):

{
  "servers": {
    "my-mcp-server": {
      "type": "sse",
      "url": "https://necessary-fuchsia-cicada.fastmcp.app/mcp"
    }
  }
}

Observed Behavior

1. Tool Schema View: Shows empty properties: {} (expected for elicitation tools)

2. Tool Execution: When calling the tool:

   • No elicitation form appears
   • Tool execution hangs or times out
   • No error messages shown
   • Server logs show elicitation request initiated but no response received

3. Comparison with Working Scenarios:

   • Local (stdio): Elicitation form appears immediately, works perfectly
   • MCP Inspector (HTTP/remote): Elicitation form appears, works perfectly
   • Remote (SSE): Elicitation form never appears, execution hangs

Root Cause Hypothesis

Based on testing evidence:

1. Server is correct: MCP Inspector proves remote elicitation works with HTTP transport
2. Cursor supports elicitation: Works perfectly with stdio transport
3. Issue is transport-specific: SSE transport in Cursor may not properly handle elicitation state management

According to MCP specification:

• For remote servers, elicitation state MUST be bound to user identity, not session IDs
• Remote servers require proper user identification from MCP authorization

Questions

1. Is this a known issue with FastMCP + remote SSE transport + elicitation?
2. Does Cursor fully support remote elicitation over SSE transport?
3. Are there any FastMCP configuration options needed for remote elicitation?
4. Should I use HTTP transport instead of SSE for remote elicitation?
5. Is there a workaround to make elicitation work with remote FastMCP servers?

What I've Tried

• ✅ Verified server code follows FastMCP elicitation patterns
• ✅ Tested with MCP Inspector (works - proves server is correct)
• ✅ Tested locally with stdio (works - proves Cursor supports elicitation)
• ✅ Added logging to track elicitation requests
• ✅ Verified tool schema is correct (empty properties for elicitation tools)
• ❌ Tried different FastMCP versions
• ❌ Checked server logs (shows elicitation initiated but no client response)

Environment

• FastMCP Version: Latest
• Python Version: 3.14
• Cursor Version: Latest
• Deployment Platform: fastmcp.cloud
• Transport: SSE (Server-Sent Events)

Additional Context

The MCP Elicitation Specification states:

"For remote MCP servers, user identification MUST be derived from credentials acquired via MCP authorization when possible (e.g. sub claim)"

"For remote servers, elicitation state MUST be bound to user identity, NOT associated with session IDs alone"

References:

• MCP Elicitation Spec
• FastMCP Documentation
• Cursor MCP Docs

Expected Behavior

When calling a tool that uses ctx.elicit():

1. Tool execution should pause
2. Elicitation form should appear in the client UI
3. User fills the form
4. Tool continues with the collected data
5. Tool returns result

Actual Behavior

1. Tool execution starts
2. Elicitation form never appears
3. Tool execution hangs indefinitely
4. No error message shown
5. Server logs show elicitation request but no client response

---

Has anyone successfully gotten FastMCP elicitation to work with remote SSE transport? Any guidance would be greatly appreciated!