cmux

cmux is an open-source macOS terminal built specifically for multitasking with AI coding agents, combining a Ghostty-based terminal emulator with a vertical tab sidebar and a built-in browser. Designed for developers who run multiple coding agents like Claude Code and Codex simultaneously, it provides a unified workspace where each agent session gets its own dedicated pane. The core value proposition is giving developers the ability to manage numerous agent interactions efficiently without losing context or switching between multiple windows. By integrating vertical tabs, notifications, and a scriptable browser directly into the terminal, cmux transforms the traditional terminal experience into a control center for AI-assisted development. It leverages libghostty for GPU-accelerated rendering and automatically inherits your existing Ghostty configuration for themes, fonts, and colors.

Running multiple AI coding agents in parallel with a standard terminal quickly becomes chaotic. Traditional terminals lack per-session notifications with context, so when an agent needs input, the user sees only a generic alert like "Claude is waiting for your input" with no indication of which session or what task. With enough tabs open, it becomes impossible to identify the relevant workspace. Additionally, developers often need to interact with a web application's dev server alongside their terminal, requiring constant window switching. cmux directly addresses these pain points by providing distinct visual cues per agent, aggregating notifications in a dedicated panel, and integrating a browser that splits alongside terminal panes.

The notification system in cmux is a standout feature designed to keep developers informed without overwhelming them. Each pane can display a blue notification ring when an agent requires attention, and sidebar tabs light up with the latest notification text visible at a glance. This visual feedback instantly communicates which workspace needs action. The notification panel aggregates all pending alerts in one place, allowing the user to jump to the most recent unread with the keyboard shortcut Cmd+Shift+U. Under the hood, cmux intercepts terminal sequences such as OSC 9, OSC 99, and OSC 777, as well as providing a CLI command `cmux notify` that can be wired into agent hooks for tools like Claude Code or OpenCode. This ensures that any agent can trigger notifications that appear natively in the terminal's sidebar.

The in-app browser is another key feature, bringing a full web browser directly into the terminal environment. It is scriptable via an API ported from agent-browser, allowing AI agents to programmatically interact with web pages. Agents can snapshot the accessibility tree, obtain element references, click buttons, fill forms, and evaluate JavaScript. This enables workflows where a coding agent can test a web application on the local dev server and immediately see results. The browser can be split alongside any terminal pane, and it supports importing cookies, history, and sessions from Chrome, Firefox, Arc, and over 20 other browsers, so panes start authenticated. This integration eliminates the need to switch to an external browser when debugging or automating web tasks.