Demo MCP and others are now failing for

[namin]

Describe the bug
I created the demo MCP as in the README, and installed it with mcp install server.py. When I open Claude Desktop, I get the error messages:

2025-01-23T03:49:07.394Z [info] Connected to MCP server Demo!
2025-01-23T03:49:07.764Z [error] Error in MCP connection to server io.livecode.ch: SyntaxError: Unexpected token 'E', "Error: typ"... is not valid JSON
2025-01-23T03:49:07.818Z [error] Error in MCP connection to server Demo: SyntaxError: Unexpected token 'E', "Error: typ"... is not valid JSON
2025-01-23T03:49:07.848Z [info] MCP server Demo disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging)

To Reproduce
Follow the steps in the README for the Demo example. It works perfectly in the inspector but doesn't initialize in Claude.

Desktop:

• OS: Mac OS X

Additional context
The MCPs based on docker work perfectly and those based on this SDK seem to fail for me.

[tjroamer]

Got the same error on Windows as well.

[dino-su]

same here with mcp 1.2.0 on macOS.

[vishalagrawal-jisr]

mcp dev server.py

In inspector things are looking fine though.

I think it's trying to list templates and it gives error
resources/templates/list

Error MCP error -32601: Method not found

[klaventall]

same here with mcp 1.2.0 on macOS.

[sheffler]

I had the same error:
Unexpected token 'E', "Error: typ"... is

It had to do with UV not finding the home directory of the project/python-file.

Platform: OSX.

Fixed it by adding the --directory path in claude_desktop_config.json

    "MyServer": {
      "command": "/Users/me/.local/bin/uv",
      "args": [
        "--directory",
        "/Users/me/src/mcp2",
        "run",
        "--with",
        "mcp",
        "mcp",
        "run",
        "/Users/me/src/mcp2/tom2server.py"
      ]
    }

[wanderingnature]

have a look at #148

[Mehdi-Bl]

1.2.0 introduced breaking changes, so code need to be updated.
Had to update my own code too.

Docker work? which version already you tried?

Fixes are not complicated.

Issue example is here

"mcp>=1.1.3",

https://github.com/modelcontextprotocol/servers/blob/e055e18f8c56951203fdf8f64a811802dad8144b/src/fetch/pyproject.toml#L20C1-L20C18

instead use "mcp=1.1.3"

But I don't recommend that. Best fixing the sever code.