MCP-DSC-002

DiscoverResult advertises supported protocol versions

“`supportedVersions`: Protocol versions the server supports. The client should choose one of these for subsequent requests.” — spec anchor

How to fix this

Return a `supportedVersions` array in the DiscoverResult naming every protocol revision the server accepts. The client selects one from that list for its subsequent requests.

Example: failing and passing

The DiscoverResult has no supportedVersions array, so the client has nothing to choose a version from.

Violates MCP-DSC-002 · JSON

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "resultType": "complete",
    "capabilities": {"tools": {}},
    "ttlMs": 3600000,
    "cacheScope": "public"
  }
}

The DiscoverResult lists the protocol versions the server supports in supportedVersions.

Complies with MCP-DSC-002 · JSON

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "resultType": "complete",
    "supportedVersions": ["2026-07-28"],
    "capabilities": {"tools": {}},
    "ttlMs": 3600000,
    "cacheScope": "public"
  }
}

How the validator checks this

Probe P1.1, against a streamable-http server on the modern protocol. What it reports:

pass: DiscoverResult advertises supportedVersions
fail: DiscoverResult has no supportedVersions field — it is required, and is how a client chooses the version for subsequent requests

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-DSC-001, MCP-DSC-003, MCP-DSC-004, MCP-DSC-005, MCP-STL-003, MCP-RES-001, MCP-RES-002, MCP-RES-005.

Check your own server against MCP-DSC-002

Probe P1.1 checks MCP-DSC-002 in the same request as 8 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: server/discover explained.

Other Discovery and capabilities rules

MCP-DSC-001server/discover is implemented
MCP-DSC-003Advertised versions include a currently-supported revision
MCP-DSC-004Extension identifiers use a valid non-reserved reverse-DNS prefix
MCP-DSC-005Results carry io.modelcontextprotocol/serverInfo in _meta