magmux

Minimal terminal multiplexer written in Go. Zero third-party dependencies.

A port of MTM (Rob King) from C to Go, designed as a lightweight pane splitter for running multiple terminal applications side by side.

Install

# Homebrew (macOS/Linux)
brew tap MadAppGang/tap && brew install magmux

# Go install
go install github.com/MadAppGang/magmux@latest

# From source
git clone https://github.com/MadAppGang/magmux
cd magmux && go build -o magmux .

Usage

# Default: 3 panes with your shell
magmux

# Custom commands in each pane
magmux -e 'htop' -e 'vim' -e 'bash'

# Two coding agents side by side
magmux -e 'claude' -e 'opencode'

Controls

Key	Action
Ctrl-G q	Quit
Ctrl-G Tab	Switch focus to next pane
Mouse click	Switch focus to clicked pane
Mouse drag	Select text (auto-copies to clipboard)

Layout

With 3 commands, magmux creates this layout:

┌──────────────────┬──────────────────┐
│   Command 1      │   Command 2      │
│   (top-left)     │   (top-right)    │
├──────────────────┴──────────────────┤
│   Command 3 (bottom)                │
├─────────────────────────────────────┤
│   Status bar                        │
└─────────────────────────────────────┘

Features

• Pane splitting — horizontal and vertical with binary tree layout
• VT-100 terminal emulation — DEC ANSI state machine parser
• 256-color + truecolor — full SGR support including RGB
• Mouse support — click to focus, drag to select, auto-copy to clipboard
• Line drawing characters — G0/G1 charset switching for TUI borders
• Alt screen — proper handling for vim, htop, Claude Code, OpenCode
• SIGWINCH — automatic resize when terminal size changes
• Scrollback buffer — 1000 lines per pane
• Zero dependencies — only golang.org/x/sys and golang.org/x/term

Architecture

Host Terminal
  └── magmux (raw mode + mouse tracking)
       ├── Pane 1 (PTY + VT parser + screen buffer)
       ├── Pane 2 (PTY + VT parser + screen buffer)
       └── Pane 3 (PTY + VT parser + screen buffer)

Each pane runs a goroutine reading from its PTY, parsing VT escape sequences into a cell grid. The render loop checks dirty flags and only redraws when content changes.

Key design: child processes see TERM=screen-256color, which limits escape sequences to what the multiplexer supports — the same approach tmux and MTM use.

Configuration

Env Variable	Default	Description
MAGMUX_SEL_FG	0 (black)	Selection foreground (256-color index)
MAGMUX_SEL_BG	220 (yellow)	Selection background (256-color index)
MAGMUX_DEBUG	(unset)	Enable debug logging to /tmp/magmux-debug.log

Why Go?

The original MTM is ~1,800 lines of C using ncurses. magmux is ~2,100 lines of Go with no ncurses dependency — raw ANSI escape codes to stdout. Go provides:

• Memory safety (no buffer overflows in escape sequence parsing)
• Goroutine-per-pane concurrency (simpler than C's select() loop)
• Static binary distribution (no ncurses/libc dependency)
• Accessible to teams that don't maintain C code

License

MIT