Missing Mcp-Session-Id

no-session-id · CORS & headers

Endpoint (Streamable HTTP)

https://chaos-mcp.thomascdnns.com/s/no-session-id/mcp

On the wire — recorded from a real request

Symptom

what you'll observe

Session can't be resumed; some clients re-initialize on every call or drop the stream.

Cause

what this reproduces

Server never returns the Mcp-Session-Id header on initialize.

Fix

how you'd resolve it

Emit Mcp-Session-Id on initialize and accept it on subsequent requests.

Try it with curl

bash

curl -sS -X POST \
  https://chaos-mcp.thomascdnns.com/s/no-session-id/mcp \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/json' \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "initialize",
    "params": {
      "protocolVersion": "2024-11-05",
      "capabilities": {},
      "clientInfo": {"name": "curl", "version": "1"}
    }
  }'