Connection to MCP server timed out using claude code.

[ammkrn]

I'm on a new nixos installation 25.05 warbler, using claude code 0.2.109. I got everything set up on another machine fine using json and the uvx invocation; when I tried the nix version claude mcp add-json nixos-mcp '{"command": "nix","args": ["run", "github:utensils/mcp-nixos", "--"]}' on the nixos machine, I initially got some errors of the form

[
  {
    "error": "Connection failed: Connection to MCP server \"nixos-mcp\" timed out after 30000ms",
    "timestamp": "2025-06-XXTXX:XX:XX.XXXZ",
    "sessionId": "...",
    "cwd": "/home/user/somedir"
  }
]

Eventually I ran claude with claude --mcp-debug and there was a connection, I'm not sure if by coincidence or whether it was the debug command itself that caused some side effect.

Feel free to close if "wont' investigate, don't care". Certainly not a blocking issue since it sort of resolved itself, but spooky action at a distance.

[jamesbrink]

Thanks for reporting this I’ll look into it more, and see if there’s any way to resolve this. I suspect this happens on the first pull and simply times out waiting. At the very least I should document this behavior

[ncaq]

It worked fine in my Claude Code environment.
The setup method is the same as the command you provided.

claude mcp add-json nixos-mcp '{"command": "nix","args": ["run", "github:utensils/mcp-nixos", "--"]}'

I paste the logs showing it's working below.

2025-06-21T10:03:23 ❯ claude
╭───────────────────────────────────────────────────╮
│ ✻ Welcome to Claude Code!                         │
│                                                   │
│   /help for help, /status for your current setup  │
│                                                   │
│   cwd: /home/ncaq/dotfiles                        │
╰───────────────────────────────────────────────────╯


 ※ Tip: Use /memory to view and manage Claude memory

> /mcp 
  ⎿  (no content)

> nixpkgsで公開されているclaude codeのバージョンは? MCPを使って調べて。

● nixpkgsで公開されているClaude Codeのバージョンを調べます。

● nixos-mcp:nixos_search (MCP)(query: "claude-code", search_type: "packages")
  ⎿  Found 20 packages matching 'claude-code':

     • claude-code (1.0.29)
     … +58 lines (ctrl+r to expand)

● claude-codeのパッケージが見つかりました。もう少し詳しい情報を確認します。

● nixos-mcp:nixos_info (MCP)(name: "claude-code", type: "package")
  ⎿  Package: claude-code                                                                                              
     Version: 1.0.29
     Description: Agentic coding tool that lives in your terminal, understands your codebase, and helps you code faster
     … +2 lines (ctrl+r to expand)

● 他のチャンネルのバージョンも確認してみます。

● nixos-mcp:nixos_info (MCP)(name: "claude-code", type: "package", channel: "stable")
  ⎿  Package: claude-code                                                                                                 
     Version: 0.2.109
     Description: An agentic coding tool that lives in your terminal, understands your codebase, and helps you code faster
     … +2 lines (ctrl+r to expand)

● nixpkgsで公開されているClaude Codeのバージョンは以下の通りです：

  - unstable: 1.0.29
  - stable: 0.2.109

  unstableチャンネルの方が新しいバージョン（1.0.29）が提供されています。