MCP tool call with Object type parameter does not work

[sonowz]

Hi,
Thank you for the wonderful product you've created and continuing to develop.

What happened?

When an Agent calls MCP tool that has parameter defined as an Object or dict in Python, the parameter gets transmitted as an empty object.
For example, a tool call with parameter

{
  "param": {"a": true, "b": "string"}
}

is sent to MCP server as

{
  "param": {}
}

For troubleshooting, I noticed an interesting behavior: the web UI initially shows the full parameter value at first, but it becomes {} within a second.

Version Information

bc690cc
(I've also reproduced the bug in the master branch version from less than a week ago)

Steps to Reproduce

1. Run the example MCP server

from mcp.server.fastmcp import FastMCP

mcp = FastMCP("echo")

@mcp.tool()
def echo(param: dict):
    """Echoes the input parameter"""
    return param

if __name__ == "__main__":
    mcp.run()

2. Add it to LibreChat
3. Calling the echo tool in LibreChat sends nothing but empty object

Screenshots

Here's a conversation that uses example MCP server above:

Code of Conduct

• I agree to follow this project's Code of Conduct

[danny-avila]

Hey thanks for the report. I'm taking a look at this to determine how we can handle open-ended properties for inputs like this.

[danny-avila]

Closed by #6720

[inv-Eldho]

@danny-avila

Ongoing Issue with add_fields Tool – Properties Being Passed as Empty

Hi,

We are experiencing the same issue again when attempting to pass field properties from LibreChat to MCP. The properties object becomes empty during the process, specifically when using the add_fields tool.

Prompt i tried is :
Add these field into app

{
"app": 810,
"properties": {
type: "SINGLE_LINE_TEXT"
code: "minutes_id",
label: "minutes_id" }
}
}

Here’s the request we’re making:

Running add_fields tool

{
  "app_id": 810,
  "properties": {
    "minutes_id": {
      "code": "minutes_id",
      "type": "SINGLE_LINE_TEXT",
      "label": "minutes_id",
      "required": false
    }
  }
}

Result:
We continue to encounter a technical issue when trying to add the minutes_id field to the app. The system returns the following error:

"properties requires at least one field definition"

Thank you.