MCP server/discover against Sume's hosted endpoint

Sume's hosted MCP server does not implement server/discover. The JSON-RPC dispatcher handles initialize, ping, tools/list and tools/call, and any other method is rejected with error code -32601 (method not found). Read the version and capabilities from initialize, and the tool catalog from tools/list.

Spec facts are from the 2026-07-28 server/discover page, read 2026-09-30. Sume facts are from the packages/mcp-server source and the MCP quickstart. Which spec version the server speaks is covered in this post.

What does server/discover do in the spec?

The page says it lets a client query a server's supported protocol versions, capabilities and identity before sending other requests. The response carries supportedVersions, capabilities, an optional instructions string, and caching hints (ttlMs, cacheScope). The same page says servers MUST implement it, while calling it is optional for clients, which may invoke any RPC inline and handle UnsupportedProtocolVersionError. Sume's server declares 2025-11-25 as its newest version, a revision that predates this method, so the gap is a version gap, not a documented Sume decision.

What does Sume's endpoint answer instead?

Method dispatch in the server source is a fixed switch; the default branch throws JsonRpcMethodNotFoundError, which the handler turns into a JSON-RPC error with code -32601. So a server/discover request gets that error, not a result object.

Where do I read the same information?

From initialize. The server echoes the requested protocolVersion when it is in its supported list (2025-03-26, 2025-06-18, 2025-11-25), and otherwise answers with 2025-11-25. Its capabilities object declares tools with listChanged set to false. Tool names come from tools/list; see the tools/list caching post.

const res = await fetch("https://mcp.sume.com/mcp", {
  method: "POST",
  headers: {
    "Content-Type": "application/json",
    Accept: "application/json, text/event-stream",
    Authorization: "Bearer " + process.env.SUME_API_KEY,
  },
  body: JSON.stringify({ jsonrpc: "2.0", id: 1, method: "server/discover" }),
});
console.log(res.status, await res.text()); // expect error code -32601

Should my client call it anyway?

Since clients are not required to call it, treat -32601 as "not available" and fall back to initialize. A client that probes first should not fail hard on that error. I did not verify how any specific client library reacts, so test yours against the endpoint.