# Connect a Swift MCP client

Source: https://libtmux.org/en/swift/latest/mcp/guides/

> Build libtmux-mcp and select its tmux endpoint and tool authority through environment variables.

Build the Swift executable and have the MCP client launch it.
Use the package's supported Swift toolchain and make tmux available to
the client process.

## Build and launch

From the Swift repository:

```console
$ swift build --product libtmux-mcp
```

The debug executable is written under `.build/debug`.
Run an inspection surface on a named socket:

```console
$ LIBTMUX_SOCKET=docs-agent LIBTMUX_TOOLSETS=inspect \
    .build/debug/libtmux-mcp
```

It waits for MCP messages. The executable accepts no flags; configure
its endpoint through the environment.

## Connect a client

If the executable is on the client's `PATH`, use this
`mcpServers` entry. Otherwise set `command` to its actual built location.

```json
{
  "mcpServers": {
    "tmux-swift": {
      "command": "libtmux-mcp",
      "env": {
        "LIBTMUX_SOCKET": "docs-agent",
        "LIBTMUX_TOOLSETS": "inspect"
      }
    }
  }
}
```

`LIBTMUX_SOCKET_PATH` and `LIBTMUX_SOCKET` are mutually exclusive.
`LIBTMUX_TMUX_BIN` selects the tmux executable.

## Verify and narrow the surface

Ask the client to list sessions and read `tmux://capabilities`.
Retain opaque references from listings for follow-up calls.

To allow only listing and window creation, set `LIBTMUX_TOOLSETS` to
an empty string and `LIBTMUX_TOOLS=list_sessions,create_window`.
Reconnect after changing environment variables.

Invalid tool selections fail startup; inspect stderr diagnostics. A stale pane reference needs a fresh listing,
not another spelling of the same raw ID.

[Executable contract](https://github.com/libtmux/libtmux-swift/blob/254f8b2be7eb60cacc3ffcb3ea8e456784f582df/Sources/libtmux-mcp/README.md).