Cinch MCP server

@cinch-codes/mcp

MCP server for Cinch. Gives your AI assistant a real sandbox to run code in.

Without it, an assistant writes code and you run it yourself. With it, the assistant runs the code and reads the actual output — inside a gVisor-isolated container on Cinch's infrastructure, with no access to your machine, filesystem, or local network.

Pay per execution. No subscription floor.

Setup

Get an API key at cinch.codes, then add the server to your MCP client.

Claude Desktop — claudedesktopconfig.json:

{
  "mcpServers": {
    "cinch": {
      "command": "npx",
      "args": ["-y", "@cinch-codes/mcp"],
      "env": {
        "CINCH_API_KEY": "cinch_live_..."
      }
    }
  }
}

Claude Desktop on Windows — same file, but Windows can't spawn npx directly, so wrap it with cmd /c:

{
  "mcpServers": {
    "cinch": {
      "command": "cmd",
      "args": ["/c", "npx", "-y", "@cinch-codes/mcp"],
      "env": {
        "CINCH_API_KEY": "cinch_live_..."
      }
    }
  }
}

Claude Code (macOS/Linux):

claude mcp add --scope user cinch -e CINCH_API_KEY=cinch_live_... -- npx -y @cinch-codes/mcp

Claude Code (Windows):

claude mcp add --scope user cinch -e CINCH_API_KEY=cinch_live_... -- cmd /c npx -y @cinch-codes/mcp

Cursor — .cursor/mcp.json, same shape as the Claude Desktop config above.

Restart the client. That's it — no install step, npx fetches it on first run.

What it exposes

execute_code

Runs a self-contained Python or JavaScript program and returns stdout, stderr, exit code, and duration.

Each call gets a clean sandbox. State does not persist between calls, so every snippet needs to stand on its own.

The sandbox environment

Deliberately minimal. Worth knowing before you wonder why an import failed:

The tool description tells the model all of this up front, so it writes stdlib-only code instead of reaching for numpy and failing on the first call.

Configuration

Troubleshooting

Windows: "Failed to connect" in claude mcp list — you're missing the cmd /c wrapper. Windows resolves npx to a batch script that can't be spawned directly; re-add the server using the Windows command above.

Windows: npm error ENOENT ... AppData\Roaming\npm — some Node installs never create npm's global folder, and npx refuses to run without it. Create it once and retry:

mkdir %APPDATA%\npm

Server exits immediately with "CINCHAPIKEY is not set" — the env var didn't reach the server. In Claude Code, put -e CINCHAPIKEY=... before the server name in claude mcp add. In config files, check the env block is inside the cinch entry.

Debugging any connection failure — run the server directly to see the real error instead of a generic status:

Shortened. The full README is on GitHub.