MCP Server Does Not Expose /run Endpoint with sse Transport (Returns Not Found#)

[grahama1970]

Description

When running an MCP server using FastMCP with sse transport, the expected /run endpoint is not exposed. Any HTTP requests to /run, /tools/list, or /tools/call return a 404 Not Found# response. This happens even with a minimal example script.

I’ve tested this both locally (outside of Docker) and in Docker, and neither setup works. The issue persists even when using a simple example.

---

Steps to Reproduce

1. Install mcp[cli] version 1.3.0 using uv:

   uv pip install "mcp[cli]==1.3.0"

2. Confirm the installed version:

   uv pip show mcp

   Output:

   Name: mcp
   Version: 1.3.0
   Location: /home/grahama/workspace/experiments/mcp-server-arangodb/.venv/lib/python3.10/site-packages
   Requires: anyio, httpx, httpx-sse, pydantic, pydantic-settings, sse-starlette, starlette, uvicorn
   Required-by: arango-mcp
   

3. Create a minimal MCP server script (simple_mcp.py):

   from mcp.server.fastmcp import FastMCP
   
   mcp = FastMCP("Echo")
   
   @mcp.tool()
   def echo(message: str) -> str:
       """Echo back the input message."""
       return f"Echo: {message}"
   
   if __name__ == "__main__":
       mcp.run(transport="sse")  # Use SSE transport for HTTP

4. Run the server:

   python simple_mcp.py

5. Query the /run endpoint using curl:

   curl -X POST http://localhost:8000/run \
       -H "Content-Type: application/json" \
       -d '{
           "jsonrpc": "2.0",
           "method": "tools/call",
           "params": {
               "name": "echo",
               "arguments": {
                   "message": "Hello, MCP!"
               }
           },
           "id": 1
       }'

---

Expected Behavior

The server should expose the /run endpoint, and querying it with a valid JSON-RPC request should return a response like this:

{
    "jsonrpc": "2.0",
    "id": 1,
    "result": "Echo: Hello, MCP!"
}

---

Actual Behavior

The server responds with:

Not Found#

This happens for any requests to /run, /tools/list, or /tools/call.

---

Environment

• Python Version: 3.10.16

• MCP Version: 1.3.0 (installed via uv)

• OS: Ubuntu 22.04 (local environment)

• Dependency Manager: uv

• pyproject.toml:

  [project]
  name = "arango_mcp"
  version = "0.1.0"
  description = "ArangoDB MCP Server"
  authors = [
      {name = "Graham Anderson", email = "[email protected]"}
  ]
  dependencies = [
      "python-arango>=7.9.1",
      "loguru>=0.7.3",
      "mcp[cli]==1.3.0",
  ]
  requires-python = ">=3.10.16"
  
  [build-system]
  requires = ["poetry-core>=1.0.0"]
  build-backend = "poetry.core.masonry.api"
  
  [project.scripts]
  arango-mcp = "arango_mcp.main:main"

• Running Locally: Yes (outside Docker), but Docker also fails.

---

Debugging Steps Taken

1. Verified that mcp[cli] version is 1.3.0.
2. Confirmed that tools are registered by logging mcp.tools.
3. Tested alternate endpoints (/tools/list, /tools/call) — all return Not Found#.
4. Switched to stdio transport — this works as expected:

   (echo '{"jsonrpc": "2.0", "method": "tools/call", "params": {"name": "echo", "arguments": {"message": "Hello, MCP!"}}, "id": 1}'; cat) | python simple_mcp.py

5. Checked port binding — no conflicts on port 8000.

Please provide guidance on how to expose and query endpoints when using HTTP (sse) transport.

[wangheng0206]

1.you need use http get endpoint

2. and then you can use result to get tools

3. you can use command "mcp dev server.py" and find paramters