different-ai/openwork · error · SafeProbeFailure

unsupported_protocol_version

unsupported_protocol_version

Error message

unsupported_protocol_version

What it means

requireSupportedProtocolVersion throws SafeProbeFailure("unsupported_protocol_version") when the initialize result's protocolVersion is a well-formed string but does not exactly equal MCP_PROTOCOL_VERSION. The probe pins one protocol version and refuses endpoints negotiating a different one.

Solutions

1. Upgrade or downgrade the MCP server so its protocolVersion matches the version pinned by this client build
2. Update the client's MCP_PROTOCOL_VERSION constant to the version the server speaks (via a coordinated release)
3. Check release notes of both sides for a protocol version bump
4. Test with a reference MCP server to confirm which version it negotiates

Example fix

// before (server)
protocolVersion: "2025-03-26"
// after (match client constant)
protocolVersion: MCP_PROTOCOL_VERSION // e.g. "2024-11-05"

const version = initResult.protocolVersion;
if (typeof version === "string" && version !== SUPPORTED_VERSIONS) {
  console.warn(`server speaks MCP ${version}; client pins ${SUPPORTED_VERSIONS} — align versions before probing`);
}

function isSupportedProtocolVersion(v: unknown): v is string {
  return typeof v === "string" && v === MCP_PROTOCOL_VERSION;
}

try {
  requireSupportedProtocolVersion(initResult);
} catch (e) {
  if (e instanceof SafeProbeFailure && e.code === "unsupported_protocol_version") {
    // surface a clear upgrade instruction; optionally retry against a version-matched endpoint
  } else throw e;
}

When it happens

Trigger: Server returns any valid string protocolVersion other than the pinned MCP_PROTOCOL_VERSION constant (e.g. older '2024-10-07' or newer date-versioned releases).

Common situations: Client and server upgraded at different times so MCP protocol versions drifted; server negotiates versions per spec's date-based scheme while the probe expects one fixed value; custom MCP server fork with its own version string.

Related errors

• MCP_UNSUPPORTED_VERSION
• MCP_VERSION
• is no longer available as your reconnectable account.
• AUTH_RESOURCE_DISCOVERY
• Authorization for did not finish. Complete it in the…

AI-assisted analysis of different-ai/openwork@2b7df46e8a (2026-09-01). Data as JSON: /api/errors/3e8ee2737da30919. Report an issue: GitHub.

Appendix: source

Thrown at apps/server/src/agent-context-cloud-probe.ts:542

  return messages[0];
}

function parseJsonRpcResult(payload: unknown, requestId: string): Record<string, unknown> {
  if (!isRecord(payload) || payload.jsonrpc !== "2.0") {
    throw new SafeProbeFailure("invalid_jsonrpc_envelope");
  }
  if (Object.hasOwn(payload, "error")) throw new SafeProbeFailure("jsonrpc_error");
  if (payload.id !== requestId) throw new SafeProbeFailure("request_id_mismatch");
  if (!isRecord(payload.result)) throw new SafeProbeFailure("invalid_jsonrpc_envelope");
  return payload.result;
}

function requireSupportedProtocolVersion(initializeResult: Record<string, unknown>): void {
  const version = initializeResult.protocolVersion;
  if (typeof version !== "string" || version.length === 0 || version.length > MAX_PROTOCOL_HEADER_LENGTH) {
    throw new SafeProbeFailure("invalid_jsonrpc_envelope");
  }
  if (version !== MCP_PROTOCOL_VERSION) throw new SafeProbeFailure("unsupported_protocol_version");
}

function validateCatalog(rpcResult: Record<string, unknown>): { toolIds: string[]; totalToolCount: number } {
  if (rpcResult.nextCursor !== undefined && rpcResult.nextCursor !== null) {
    throw new SafeProbeFailure("pagination_unsupported");
  }
  if (!Array.isArray(rpcResult.tools) || rpcResult.tools.length > MAX_TOOL_COUNT) {
    throw new SafeProbeFailure("invalid_catalog");
  }
  const seen = new Set<string>();
  for (const tool of rpcResult.tools) {
    if (!isRecord(tool) || typeof tool.name !== "string" || tool.name.length > MAX_TOOL_ID_LENGTH || !TOOL_ID.test(tool.name)) {
      throw new SafeProbeFailure("invalid_catalog");
    }
    if (seen.has(tool.name)) throw new SafeProbeFailure("invalid_catalog");
    seen.add(tool.name);
  }
  // Additional provider tools are forward-compatible and allowed, but never

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