I run a lot of Claude Code and Codex sessions in parallel. I was using Ghostty with a bunch of split panes, and relying on native macOS notifications to know when an agent needed me. But Claude Code's notification body is always just "Claude is waiting for your input" with no context, and with enough tabs open, I couldn't even read the titles anymore.

I tried a few coding orchestrators but most of them were Electron/Tauri apps and the performance bugged me. I also just prefer the terminal since GUI orchestrators lock you into their workflow. So I built cmux as a native macOS app in Swift/AppKit. It uses libghostty for terminal rendering and reads your existing Ghostty config for themes, fonts, colors, and more.

The main additions are the sidebar and notification system. The sidebar has vertical tabs that show git branch, working directory, listening ports, and the latest notification text for each workspace. The notification system picks up terminal sequences (OSC 9/99/777) and has a CLI (cmux notify) you can wire into agent hooks for Claude Code, OpenCode, etc. When an agent is waiting, its pane gets a blue ring and the tab lights up in the sidebar, so I can tell which one needs me across splits and tabs. Cmd+Shift+U jumps to the most recent unread.

The in-app browser has a scriptable API ported from agent-browser [1]. Agents can snapshot the accessibility tree, get element refs, click, fill forms, evaluate JS, and read console logs. You can split a browser pane next to your terminal and have Claude Code interact with your dev server directly.

Everything is scriptable through the CLI and socket API – create workspaces/tabs, split panes, send keystrokes, open URLs in the browser.

Demo video: https://www.youtube.com/watch?v=i-WxO5YUTOs

Repo (AGPL): https://github.com/manaflow-ai/cmux

[1] https://github.com/vercel-labs/agent-browser

Hey, this looks seriously awesome. Love the ideas here, specifically: the programmability (I haven't tried it yet, but had been considering learning tmux partly for this), layered UI, browser w/ api. Looking forward to giving this a spin. Also want to add that I really appreciate Mitchell Hashimoto creating libghostty; it feels like an exciting time to be a terminal user.

Some feedback (since you were asking for it elsewhere in the thread!). Happy to go into more detail about any of these if it's helpful:

- It's not obvious/easy to open browser dev tools (cmd-alt-i didn't work), and when I did find it (right click page -> inspect element) none of the controls were visible but I could see stuff happening when I moved my mouse over the panel

- Would be cool to borrow more of ghostty's behavior:

  - hotkey overrides - I have some things explicitly unmapped / remapped in my ghostty config that conflict with some cmux keybindings and weren't respected

  - command palette (cmd-shift-p) for less-often-used actions + discoverability

  - cmd-z to "zoom in" to a pane is enormously useful imo

I like what you did here and with your direction with the stack. We have some common overlap. Last week I started clauding up something to manage my Claude sessions. It is built on Tauri 2 using xterm.js. It has is project-based and each project has resumable sessions. I borrowed inspiration from Happy coder and clauded an Expo app so I can claude remotely on-the-go. It has been a force multiplier in my clauding with developing new features and addressing bugs and defects. It was a pretty amazing feeling when I started using it to further its own development. There's a slew of other features as I adapt it to my development style.

I had sort of the same idea. https://wingthing.ai/ This idea started at “sandbox” and worked its way toward “remote access”. But same thoughts about muxing sessions. Love being able to leave and reattach while an agent is working. I’ll give yours a shot!

Have you looked into zmx? [0]

It doesn't have built-in notifications and there's no panel to see all the open sessions, but I wonder how hard that would be to add.

I've used zmx since I ran into it a few weeks ago. Uses libghostty as well. It's great because it allows me to replace tmux completely in all my ssh sessions, and can keep one session per assistant.

[0]: https://github.com/neurosnap/zmx

With this one, small tweak it is perfect:

osascript << 'EOF' use framework "Foundation" use framework "AppKit"

set ghosttyIconPath to "/Applications/Ghostty.app/Contents/Resources/Ghostty.icns" set cmuxAppPath to "/Applications/cmux.app"

-- Read the icon file set iconImage to current application's NSImage's alloc()'s initWithContentsOfFile:ghosttyIconPath

-- Set it as the custom icon for cmux.app current application's NSWorkspace's sharedWorkspace()'s setIcon:iconImage forFile:cmuxAppPath options:0 EOF

((The ghost pairs well with Kiro, what can I say?))

Just took it for a spin, thought it was pretty nice. Some quirks with the tab dragging, you never really know what it's going to do on mouseup, a drop-target indicator would help.

Would love to be able to color the sidebar tab.

Nice work!

Looks really useful! Does this support the new Claude Code agent teams feature, so it will open all the team members in their own pane?

Looks like this could be really cool, but it's a buggy mess. Can't switch top tabs, can't close tabs. Once I lose focus in a tab, I can't ever type again in that terminal tab. Can't switch between the different sidebar tabs, either.

Hm... any idea how I might script `git worktree` into the new-pane action?

Currently experimenting with agent-of-empires for tmux+worktrees to parallelize code changes.

Nice. I should add notifications to https://github.com/rcarmo/webterm - I already have sparklines as a CPU usage indicator and live thumbnails, but a visual highlight should be easy to add.

This is pretty slick, man. The only thing is that the Ctrl-Cmd-] is too hard to press but I'll just use the number thing.

Awesome work, keen to try it out tomorrow. Can I make the notifications work with Gemini CLI and Kiro CLI too?

Gave this a run and it was pretty intuitive. Good work!

vertical tabs are a great idea for ghostty!

Good idea, but I don't want to move to another terminal now, will stick with Ghossty

This looks cool. I honestly haven’t ever thought about using vertical tabs in a terminal window but that seems nice.

One question though, have you thought about trying to upstream any of this into Ghostty instead of making an entirely different app?

18 (!) releases in two days. This is some really fast coding.