Latest version (V9.0.1) broke the HTTP server

[Travistyse]

x Failed to resolve --with requirement
`-> Git operation failed

I'm now seeing this every time I try to run the server - has been working without issues for months now - including today up until installing this update.

Unity 6.3 LTS
Dropped back down via install via URL with "https://github.com/CoplayDev/unity-mcp.git?path=/MCPForUnity#v8.7.1" and everything works again as expected. Unsure what was changed precisely but it didn't agree with my install. I'm on Windows 11.

[dsarno]

Claude desktop?

[Travistyse]

Claude desktop?

Sorry for the late reply - Claude Code in VS Code

Albeit to clarify this happens when I launch the HTTP server - it's all that it says in the terminal that pops up - am I needing to register Claude Code again or something like that after this update? I was on 8.7.1 prior and went back to it without issues and all of the previous updates never caused any breaks to happen.

[dsarno]

Try /mcp command in Claude code and choose "reconnect"

[Travistyse]

I'll give it a try tomorrow, headed to bed - but to clarify the issue isn't that Claude Code can't see the MCP server it's that when I go to launch it the server doesn't function - there's.. nothing to connect to. So unless I'm missing something this isn't likely to work? Image for reference.

[kwikalot]

Claude desktop?

For me it's happening on Claude Desktop - I've upgraded from 8.4 today, and I'm getting "Server disconnected"

2026-01-08T08:50:53.763Z [info] [unityMCP] Server started and connected successfully
2026-01-08T08:50:53.845Z [info] [unityMCP] Message from client: {"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0}
2026-01-08T08:50:55.908Z [info] [unityMCP] Server transport closed
2026-01-08T08:50:55.908Z [info] [unityMCP] Client transport closed
2026-01-08T08:50:55.909Z [info] [unityMCP] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log.
2026-01-08T08:50:55.909Z [error] [unityMCP] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging)
2026-01-08T08:50:55.909Z [info] [unityMCP] Client transport closed
2026-01-08T08:50:57.741Z [info] [unityMCP] Shutting down server...
2026-01-08T08:50:57.741Z [info] [unityMCP] Client transport closed

configuration is:

{
  "mcpServers": {
    "unityMCP": {
      "command": "C:\\path\\to\\uvx.exe",
      "args": [
        "--from",
        "git+https://github.com/CoplayDev/unity-mcp@v9.0.1#subdirectory=Server",
        "mcp-for-unity",
        "--transport",
        "stdio"
      ],
      "disabled": false
    }
  }
}

[dsarno]

Try one thing -- in Unity mcp editor window after you select stdio, select Claude desktop from dropdown and press configure. I'm hoping it's an issue where you have old server build files and that should clean them out.

[kwikalot]

Try one thing -- in Unity mcp editor window after you select stdio, select Claude desktop from dropdown and press configure. I'm hoping it's an issue where you have old server build files and that should clean them out.

Unfortunately this didn't help - still the same error. Here is entire log, however I don't see anything special in it

2026-01-08T13:17:16.189Z [info] [unityMCP] Initializing server...
2026-01-08T13:17:16.212Z [info] [unityMCP] Using MCP server command: C:\WINDOWS\system32\cmd.exe with args and path: {
  args: [
    '/c',
    'C:\\Users\\pawel\\AppData\\Local\\Microsoft\\WinGet\\Links\\uvx.exe',
    '--from',
    'git+https://github.com/CoplayDev/unity-mcp@v9.0.1#subdirectory=Server',
    'mcp-for-unity',
    '--transport',
    'stdio',
    [length]: 7
  ],
  paths: [
    'C:\\Users\\pawel\\AppData\\Local\\Programs\\Python\\Python313',
    'and so on...'
    '',
    [length]: 29
  ]
}
2026-01-08T13:17:16.219Z [info] [unityMCP] Server started and connected successfully
2026-01-08T13:17:16.293Z [info] [unityMCP] Message from client: {"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0}
2026-01-08T13:17:21.553Z [info] [unityMCP] Server transport closed
2026-01-08T13:17:21.554Z [info] [unityMCP] Client transport closed
2026-01-08T13:17:21.554Z [info] [unityMCP] Server transport closed unexpectedly, this is likely due to the process exiting early. If you are developing this MCP server you can add output to stderr (i.e. `console.error('...')` in JavaScript, `print('...', file=sys.stderr)` in python) and it will appear in this log.
2026-01-08T13:17:21.554Z [error] [unityMCP] Server disconnected. For troubleshooting guidance, please visit our [debugging documentation](https://modelcontextprotocol.io/docs/tools/debugging)
2026-01-08T13:17:21.554Z [info] [unityMCP] Client transport closed
2026-01-08T13:17:23.209Z [info] [unityMCP] Shutting down server...
2026-01-08T13:17:23.209Z [info] [unityMCP] Client transport closed

[jtj8412]

Same error here.
case 1. on Claude Desktop
case 2. MCP HTTP Start on Unity (for Claude Code)

[bruno1308]

Same here:

This works
uvx.exe --from git+https://github.com/CoplayDev/unity-mcp@v8.7.1#subdirectory=Server mcp-for-unity --transport http --http-url http://localhost:8080

This DOESN'T work
uvx.exe --from git+https://github.com/CoplayDev/unity-mcp@v9.0.1#subdirectory=Server mcp-for-unity --transport http --http-url http://localhost:8080

The only difference is the version

Some other Info:

Windows 10
Unity 6.2
VSCode 1.105.1
git version 2.52.0.windows.1

[dsarno]

Issue identified -- working on a fix. Should be up within next hour.

[dsarno]

This is fixed in v9.0.2. Please update and let us know if you continue to see issues. Thanks all.

#534

[jtj8412]

This is fixed in v9.0.2. Please update and let us know if you continue to see issues. Thanks all.

#534

Same issue 9.0.2 on Claude Desktop, but 8.7.1 work

mcp config

"unityMCP": {
      "command": "C:\\WINDOWS\\system32\\cmd.exe",
      "args": [
        "/c",
        "C:\\Users\\{MyUserName}\\AppData\\Local\\Microsoft\\WinGet\\Links\\uvx.exe",
        "--from",
        "git+https://github.com/CoplayDev/unity-mcp@v9.0.2#subdirectory=Server",
        "mcp-for-unity",
        "--transport",
        "stdio"
      ]
    }

mcp log

2026-01-08T15:25:15.147Z [unityMCP] [info] Server started and connected successfully { metadata: undefined }
2026-01-08T15:25:15.198Z [unityMCP] [info] Message from client: {"method":"initialize","params":{"protocolVersion":"2025-06-18","capabilities":{},"clientInfo":{"name":"claude-ai","version":"0.1.0"}},"jsonrpc":"2.0","id":0} { metadata: undefined }
   Updating https://github.com/CoplayDev/unity-mcp (v9.0.2)
  × Failed to resolve `--with` requirement
  ╰─▶ Git operation failed

[kwikalot]

For me it's working for Claude Desktop in v9.0.2 now (Thanks @dsarno )

[dsarno]

@jtj8412 The fix in v9.0.2 changes the default to use PyPI instead of the git URL. A couple things to try:

1. Reconfigure your MCP client (most likely fix)

Existing client configurations may still have the old git URL. In Unity's MCP window:

• Go to Client Configuration
• Click "Configure" to regenerate the config with the new PyPI-based command

Your config should now show --from mcpforunityserver==9.0.2 instead of --from git+https://github.com/...

2. Clear the uv cache (if you tried installing before PyPI updated)

If you attempted to install right after the release, your local cache might be stale:

uv cache clean --force

Let us know if either of these helps!