koala73/worldmonitor · error

tools/list failed: HTTP ${listResp.status}

Error message

tools/list failed: HTTP ${listResp.status}

What it means

Thrown by mcpListTools after a successful initialize when the follow-up tools/list request to the MCP server returned a non-2xx HTTP status. The session was established but the tools enumeration call was rejected (expired/missing Mcp-Session-Id, auth, or upstream failure).

Source

Thrown at api/mcp-proxy.ts:322

    }, 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');
  const initData = await parseJsonRpcResponse(initResp);
  if (initData.error) throw new Error(`Initialize error: ${initData.error.message}`);
  await sendInitialized(serverUrl, headers, sessionId);
  const callResp = await postJson(serverUrl, {
    jsonrpc: '2.0', id: 3, method: 'tools/call',
    params: { name: toolName, arguments: toolArgs || {} },
  }, headers, sessionId);
  if (!callResp.ok) throw new Error(`tools/call failed: HTTP ${callResp.status}`);

View on GitHub (pinned to 9361220cc0)

Solutions

1. Check the returned status: a 404 often means the Mcp-Session-Id expired or was not forwarded
2. Ensure custom headers required by the server are applied to every request, not just initialize
3. Retry the whole connect-and-list flow to obtain a fresh session

When it happens

Trigger: Thrown at api/mcp-proxy.ts:320 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/f3c36082aba08d8c. Report an issue: GitHub.