koala73/worldmonitor · error

Initialize failed: HTTP ${initResp.status}

Error message

Initialize failed: HTTP ${initResp.status}

What it means

Thrown by mcpListTools/mcpCallTool when the JSON-RPC initialize request to the MCP server returned a non-2xx HTTP status. The endpoint was reached and answered, but rejected the initialize call (auth failure, wrong URL, gateway error), so no MCP session could be established for the tools/call or tools/list flow.

Source

Thrown at api/mcp-proxy.ts:314

}

async function sendInitialized(serverUrl, headers, sessionId) {
  try {
    await postJson(serverUrl, {
      jsonrpc: '2.0',
      method: 'notifications/initialized',
      params: {},
    }, headers, sessionId);
  } catch (error) {
    if (error instanceof McpProxySsrfError) throw error;
    /* non-fatal */
  }
}

async function mcpListTools(serverUrl, customHeaders) {
  const headers = buildHeaders(customHeaders);
  const initResp = await postJson(serverUrl, buildInitPayload(), headers, null);
  if (!initResp.ok) throw new Error(`Initialize failed: HTTP ${initResp.status}`);
  const sessionId = initResp.headers.get('Mcp-Session-Id') || initResp.headers.get('mcp-session-id');
  const initData = await parseJsonRpcResponse(initResp);
  if (initData.error) throw new Error(`Initialize error: ${initData.error.message}`);
  await sendInitialized(serverUrl, headers, sessionId);
  const listResp = await postJson(serverUrl, {
    jsonrpc: '2.0', id: 2, method: 'tools/list', params: {},
  }, headers, sessionId);
  if (!listResp.ok) throw new Error(`tools/list failed: HTTP ${listResp.status}`);
  const listData = await parseJsonRpcResponse(listResp);
  if (listData.error) throw new Error(`tools/list error: ${listData.error.message}`);
  return listData.result?.tools || [];
}

async function mcpCallTool(serverUrl, toolName, toolArgs, customHeaders) {
  const headers = buildHeaders(customHeaders);
  const initResp = await postJson(serverUrl, buildInitPayload(), headers, null);
  if (!initResp.ok) throw new Error(`Initialize failed: HTTP ${initResp.status}`);
  const sessionId = initResp.headers.get('Mcp-Session-Id') || initResp.headers.get('mcp-session-id');

View on GitHub (pinned to 9361220cc0)

Solutions

1. Check the HTTP status code in the message: 401/403 means missing or invalid credentials/headers, 404 a wrong endpoint URL
2. Verify custom headers and the serverUrl configuration for the MCP server
3. Retry transient 5xx responses once with backoff before reporting failure

When it happens

Trigger: Thrown at api/mcp-proxy.ts:312 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of koala73/worldmonitor@9361220cc0 (2026-08-21). Data as JSON: /api/errors/2c43e420979732ce. Report an issue: GitHub.