[Bug]:MCP server with custom base path "/api" instead of "mcp" or "sse" is not working

[sunvk]

🐞 Bug Summary

I have the below MCP server code with transport "streamable_http".
By default from client side to call this, the endpoint will be http://{ip_address}/mcp or for protocol SSE it will be http://{ip_address}/sse

We can override this default path as below.

mcp = FastMCP(
name="another-mcp-server",
host="0.0.0.0",
port=8007,
base_path="/api" # Add this parameter
)

But with custom path, when I try to add, Gateways/MCP Servers, it is throwing below error.

Full Test Code:

`from typing import Any
import httpx
from mcp.server.fastmcp import FastMCP
from mcp.server.fastmcp.prompts import base

Create an MCP server

mcp = FastMCP(
name="another-mcp-server",
host="0.0.0.0",
port=8007,
base_path="/api" # Add this parameter
)

Constants

MATH_API_BASE = "https://api.math.com"
USER_AGENT = "math-app/1.0"

Add a dynamic calculator resource

@mcp.resource("calculator://{operation}/{num1}/{num2}")
def get_calculator_result(operation: str, num1: float, num2: float) -> float:
"""Get a calculator result"""
if operation == "add":
return num1 + num2
elif operation == "subtract":
return num1 - num2
elif operation == "multiply":
return num1 * num2
elif operation == "divide":
if num2 != 0:
return num1 / num2
else:
return float("inf")
else:
return float("nan")

@mcp.prompt(title="Math Problem")
def solve_math_problem(problem: str) -> str:
return f"Please solve this math problem:\n\n{problem}"

@mcp.prompt(title="Unit Converter")
def convert_units(value: float, from_unit: str, to_unit: str) -> list[base.Message]:
return [
base.UserMessage("I'm converting this value:"),
base.UserMessage(f"{value} {from_unit}"),
base.AssistantMessage(f"Converting to {to_unit}..."),
]

@mcp.tool()
def power(base: float, exponent: float) -> float:
"""Get the power of a number."""
return base ** exponent

@mcp.tool()
def get_random_string(length: int) -> str:
"""Get a random string of a given length."""
import random
import string
return ''.join(random.choice(string.ascii_lowercase) for _ in range(length))

Run the server

if name == "main":
mcp.run(transport="streamable-http")
`

Thanks,
Sunish

🧩 Affected Component

Select the area of the project impacted:

• mcpgateway - API
• mcpgateway - UI (admin panel)
• mcpgateway.wrapper - stdio wrapper
• Federation or Transports
• CLI, Makefiles, or shell scripts
• Container setup (Docker/Podman/Compose)
• Other (explain below)

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🔁 Steps to Reproduce

1. ...
2. ...
3. ...

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🤔 Expected Behavior

What should have happened instead?

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📓 Logs / Error Output

Paste any relevant stack traces or logs here.
⚠️ Do not paste secrets, credentials, or tokens.

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🧠 Environment Info

You can retrieve most of this from the /version endpoint.

Key	Value
Version or commit	e.g. v0.9.0 or main@a1b2c3d
Runtime	e.g. Python 3.11, Gunicorn
Platform / OS	e.g. Ubuntu 22.04, macOS
Container	e.g. Docker, Podman, none

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🧩 Additional Context (optional)

Add any configuration details, flags, or related issues.

[crivetimihai]

Thanks for reporting, we'll try to get this addressed in the current release.

[MohanLaksh]

@crivetimihai , couldn't find reference to 'base_path' here:
https://github.com/modelcontextprotocol/python-sdk/blob/main/src/mcp/server/fastmcp/server.py

Only /mcp works

[crivetimihai]

@sunvk this looks like a limitation in FastMCP, we'll see how we can implement this. Our SSE implementation isn't using FastMCP so it should be easy for us to add support. But streamable HTTP leverages FastMCP, we'll need to figure out the best approach to add this option.