ttlMs present on all five cacheable results

How to fix this

Add `ttlMs` to the results of `tools/list`, `prompts/list`, `resources/list`, `resources/read` and `resources/templates/list`. All five are cacheable results and the field is required on each.

Example: failing and passing

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "resultType": "complete",
    "tools": [{ "name": "get_weather", "inputSchema": { "type": "object" } }],
    "cacheScope": "public"
  }
}

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "resultType": "complete",
    "tools": [{ "name": "get_weather", "inputSchema": { "type": "object" } }],
    "ttlMs": 300000,
    "cacheScope": "public"
  }
}

How the validator checks this

Probe P2.1, against a streamable-http server on the modern protocol. What it reports:

pass

ttlMs present on all … list result(s) checked

fail

ttlMs missing on

skip

No list endpoint returned a usable result, so caching metadata could not be checked

Quoted from the probe that runs this check, so it cannot drift from what the validator actually reports.

This rule is checked deterministically: a fail here is a certain violation, not an inference.

Checked in the same request as MCP-HDR-008, MCP-HDR-009, MCP-RES-003, MCP-RES-006, MCP-RES-007, MCP-ERR-003, MCP-ERR-004, MCP-ERR-005, MCP-ERR-008, MCP-CAC-002, MCP-CAC-003, MCP-CAC-004, MCP-CAC-005, MCP-SCH-001, MCP-SCH-002, MCP-SCH-003, MCP-SCH-004, MCP-SCH-005, MCP-SCH-006, MCP-SCH-007, MCP-SEC-004, MCP-SEC-005, MCP-SEC-006, MCP-DEP-005.

Check your own server against MCP-CAC-001

Probe P2.1 checks MCP-CAC-001 in the same request as 24 other rules, so one run shows your server's result for this rule next to the rest. Validate a server or read how the validator works.

Background on this topic: ttlMs and cacheScope explained.

Other Caching metadata rules

• MCP-CAC-002cacheScope present on all five cacheable results
• MCP-CAC-003cacheScope is exactly "public" or "private"
• MCP-CAC-004ttlMs is a non-negative number
• MCP-CAC-005Authenticated or personalised results are not marked cacheScope: public