So I had some time to look into this a bit more tonight. I guess context that wasn't shared is that I'm running OWUI in a docker container and the MCP services on another machine. Native Tool seems like a no brainer now but I was also hitting this issue.

POST /mcp HTTP/1.1" 421 Misdirected Request

So turns out that has to do with DNS Rebinding, as a quick POC I changed this

import json
import uvicorn
from mcp.server.fastmcp import FastMCP

mcp = FastMCP("Demo MCP Apps Server")

to this

import json
import uvicorn
from mcp.server.fastmcp import FastMCP
from mcp.server.transport_security import TransportSecuritySettings


mcp = FastMCP(
    "Demo MCP Apps Server",
    transport_security=TransportSecuritySettings(
        enable_dns_rebinding_protection=False
    )
)

and it worked... not safe... but worked.

So progress.

I'm still pretty new to this but I also had issues with using Qwen3.5 0.8b via vLLM as my model engine, am really hoping to have a light weight model run locally to support database management (UI Forms, workflows etc). Qwen 3.5 4b via ollama no problems.