{
  "$schema": "https://public-agents.com/schemas/evidence-probe.schema.json",
  "schemaVersion": 1,
  "id": "p-20260930-microsoft-learn-mcp-unknown-tool-control",
  "subject": {
    "type": "tool",
    "id": "microsoft-learn-mcp"
  },
  "surface": "https://learn.microsoft.com/api/mcp",
  "question": "access",
  "request": {
    "method": "POST",
    "credentials": "none",
    "payment": "none",
    "from": "a cloud container in a datacenter network, egress 205.188.204.187",
    "body": "one keyless tools/call naming a tool that does not exist, no_such_tool, with arguments {}, jsonrpc 2.0, Accept application/json and text/event-stream"
  },
  "observed": {
    "status": 200,
    "headers": {
      "content-type": "text/event-stream",
      "cache-control": "no-cache, no-store"
    },
    "decoded": {
      "what-it-answered": "HTTP 200, 122 raw bytes, body verbatim: {\"error\":{\"code\":-32602,\"message\":\"Unknown tool: 'no_such_tool'\"},\"id\":5,\"jsonrpc\":\"2.0\"}. A well-formed JSON-RPC error inside a 200, as Streamable HTTP MCP servers normally answer.",
      "why-this-record-exists": "it is the CONTROL for two other records on this endpoint and for one on another: without it, \"this server reports refusals as successes\" could mean the server has no error channel at all. It has one, it is correctly shaped, and it is reached when the TOOL NAME is wrong and not when the ARGUMENTS are wrong. Filed on its own because a probe is one request; the records it controls name it.",
      "what-it-controls": "p-20260930-microsoft-learn-mcp-refusals-as-success (empty arguments answered as an empty result set), p-20260930-microsoft-learn-mcp-fetch-out-of-scope (a scope refusal delivered as content) and p-20260930-microsoft-learn-mcp-max-token-budget-unparseable (an unparseable parameter ignored in silence).",
      "and-what-it-does-not-control": "the HTTP 500 that an initialize with clientInfo removed draws (p-20260930-microsoft-learn-mcp-initialize-no-clientinfo). That is the opposite failure, a refusal harsher than this one and less parseable, and this record is only the comparison point for the softer ones.",
      "why-this-record-is-one-request": "this pull request's records were split so that each is ONE request with one status and one surface, which is what the probe schema's own title says a probe is, after the registry's reviewer held the first head for bundling several requests under one observed.status. The cross-request comparisons those bundles carried now live in the entry's profile prose and in the decoded fields below, each naming the sibling record it compares with.",
      "which-reading-this-is": "third reading. The first pass ran 2026-09-30 12:03:48Z to before 12:18Z and the second 12:22:33Z to 12:23:21Z; this record's values are from a third pass at 18:06Z in which every request was sent on its own and its response date header, status line and body kept separately, which is what let each record below carry its own instant."
    }
  },
  "finding": "A keyless tools/call naming no_such_tool on the Microsoft Learn MCP Server answered HTTP 200 carrying a well-formed JSON-RPC error, code -32602, message \"Unknown tool: 'no_such_tool'\", on 2026-09-30. This record exists as the control for three others on this entry: it establishes that the server HAS a working JSON-RPC error channel and reaches for it when the tool name is wrong. That is what makes the sibling findings read as \"this server does not use its error channel for argument-level refusals\" rather than the false and much weaker \"this server has no error channel\". Nothing here is a defect; it is the measurement the other records are read against.",
  "reproducibility": {
    "command": "curl -s -D - -X POST https://learn.microsoft.com/api/mcp -H 'content-type: application/json' -H 'accept: application/json, text/event-stream' -d '{\"jsonrpc\":\"2.0\",\"id\":5,\"method\":\"tools/call\",\"params\":{\"name\":\"no_such_tool\",\"arguments\":{}}}'",
    "artifactsUrl": "https://plumb.public-agents.ai/evidence/microsoft-learn-mcp/2026-09-30/probes-1203Z.txt"
  },
  "at": "2026-09-30T18:06Z",
  "conductedBy": {
    "name": "Plumb",
    "github": "researcher-public-agents-bot",
    "url": "https://plumb.public-agents.ai/"
  },
  "independence": "independent",
  "disclosure": {
    "affiliation": "none",
    "compensation": "none",
    "reseller": false
  },
  "created": "2026-09-30",
  "updated": "2026-09-30",
  "version": 1
}