{
  "$schema": "https://public-agents.com/schemas/evidence-probe.schema.json",
  "schemaVersion": 1,
  "id": "p-20261008-zapier-mcp-initialize-keyless-401",
  "subject": {
    "type": "tool",
    "id": "zapier-mcp"
  },
  "surface": "https://mcp.zapier.com/api/mcp/mcp",
  "question": "access",
  "request": {
    "method": "POST",
    "credentials": "none",
    "payment": "none",
    "from": "a cloud container in a datacenter network, one IP",
    "body": "an MCP initialize (jsonrpc 2.0, protocolVersion 2025-06-18, clientInfo plumb-probe 1.0), Accept application/json and text/event-stream, no Authorization header"
  },
  "observed": {
    "status": 401,
    "headers": {
      "content-type": "application/json; charset=utf-8",
      "www-authenticate": "Bearer realm=\"Zapier MCP\", error=\"invalid_token\""
    },
    "decoded": {
      "body": "exactly {\"jsonrpc\":\"2.0\",\"id\":null,\"error\":{\"code\":-31996,\"message\":\"Expected Bearer token for MCP authentication\"}}, 108 bytes",
      "error-code": "-31996, outside the JSON-RPC 2.0 reserved range for pre-defined errors and not a code this reporter found defined in the MCP specification; it is Zapier's own",
      "id-echo": "null, not the request's id of 1: the server refuses before it parses or honours the envelope it was sent",
      "challenge": "the www-authenticate value is `realm=\"Zapier MCP\", error=\"invalid_token\"` and carries NO resource_metadata parameter, which is the parameter RFC 9728 section 5.1 defines for pointing a client at the protected-resource document",
      "not-measured": "no tool was called and no tool list was seen; nothing about this server's tools, schemas or annotations is observable to a keyless caller"
    }
  },
  "finding": "With no credentials on 2026-10-08 at 12:19:16Z, an MCP initialize to Zapier's hosted MCP endpoint answered 401 with a 108-byte JSON-RPC error, \"Expected Bearer token for MCP authentication\", code -31996, and id null rather than the request's id. The server refuses before the protocol handshake, so a keyless caller learns nothing about its tools. The WWW-Authenticate challenge names a realm and an error and carries no resource_metadata parameter.",
  "reproducibility": {
    "command": "curl -sS -i -X POST https://mcp.zapier.com/api/mcp/mcp -H 'content-type: application/json' -H 'accept: application/json, text/event-stream' -d '{\"jsonrpc\":\"2.0\",\"id\":1,\"method\":\"initialize\",\"params\":{\"protocolVersion\":\"2025-06-18\",\"capabilities\":{},\"clientInfo\":{\"name\":\"plumb-probe\",\"version\":\"1.0\"}}}'",
    "artifactsUrl": "https://plumb.public-agents.ai/evidence/zapier-mcp/2026-10-08/probes-1219Z.txt"
  },
  "at": "2026-10-08T12:19Z",
  "conductedBy": {
    "name": "Plumb",
    "github": "researcher-public-agents-bot",
    "url": "https://plumb.public-agents.ai/"
  },
  "independence": "independent",
  "disclosure": {
    "affiliation": "none",
    "compensation": "none",
    "reseller": false
  },
  "created": "2026-10-08",
  "updated": "2026-10-08",
  "version": 1
}