Agent Builder: MCP “Add Connector” spinner and config.allowed_tools error

API Bugs
, ,
1

Hi,

I tried to use MCP tools on agent builder but cannot retrieved anything. When i look on network log, its error 400 on versions api with these response:

{
“error”: {
“message”: “The config.allowed_tools list is empty for the standalone MCP tool node.”,
“type”: “invalid_request_error”,
“param”: “config.allowed_tools”,
“code”: null
}
}

Anyone knows how to resolve it? Thanks

2

Issue Summary
When creating a new workflow in Agent Builder and adding an MCP task, the “Add Connector” dialog never loads (infinite spinner). As a result, the MCP node has no tools configured and the workflow fails to save with an error.

Steps to Reproduce

  1. Open Agent Builder → Workflows.
  2. Create a new workflow.
  3. Add an MCP task node (e.g. “Invoke a Model Context Protocol Tool”).
  4. Click “Add” on the MCP node to open “Add Connector”.
  5. Observe: the “Add Connector” dialog shows a spinner forever and never lists any connectors or servers.
  6. Try to open “Workflow settings” or save the workflow.

Expected Behavior

  • “Add Connector” should load available MCP connectors/servers.
  • After selecting a connector, the MCP node should have at least one allowed tool, and the workflow should be created/saved successfully.

Actual Behavior

  • “Add Connector” dialog never finishes loading (spinner only).

  • No connectors are shown, so no tools can be selected.

  • When opening Workflow settings or saving, Agent Builder shows:

    Failed to create workflow: The 'config.allowed_tools' list is empty for the standalone MCP tool node.

Additional Details

  • Reproduced in multiple browsers (Chrome, plus 2 others) and with cleared cache/cookies.
  • Happens both for custom MCP and for built-in connectors (Google Drive, Booking, etc.) — the dialog never loads for any of them.
  • I am using ChatGPT with Agent Builder (GPT+ subscription), not the standalone API key in this UI.
  • The issue appears identical to:
    • “Agent Builder – When adding a MCP Server tool, UI just spins”
    • “The config.allowed_tools list is empty for the standalone MCP tool node”

Attachments

4 Likes
3

Hi @arsenynn welcome to the developer community!

Thanks for taking the time to flag this, I’ve raised the issue.

4 Likes
4

I can confirm this. Is there any way to bypass this as of now?

5

Yeah, same issue since 2 days ago!

6

Same issue here infinite loop

7

Experiencing the same issue :frowning:

8

same issue , unable to build flows

9

same here :raised_hand: unable to load the connectors

10

Should be fixed now!

Thanks for taking the time to report this, everyone!

3 Likes