---
name: cmux
description: "Control cmux workspaces, panes, surfaces, and agent sessions safely from macOS terminal workflows."
category: development
risk: critical
source: community
source_repo: davidondrej/skills
source_type: community
date_added: "2026-07-07"
author: davidondrej
tags: [cmux, terminal, agents, macos]
tools: [claude, codex]
license: "MIT"
license_source: "https://github.com/davidondrej/skills/blob/main/LICENSE"
---
## Supporting material availability

This catalog copy contains the inline guidance below, but does not include the following supporting paths. They are external prerequisites, not bundled files:

- `<support-root>/references/socket-api.md`

Obtain the required material from the [declared upstream source](https://github.com/davidondrej/skills), or from a user-provided installation of that source. Resolve each path relative to that installation, inspect its contents, and verify any applicable license and execution prerequisites. Do not run a command or claim a referenced procedure was followed until its required file exists. Do not fabricate the missing scripts or treat an unrelated file with the same name as equivalent. Independent steps fully documented here can proceed within the user’s authorized scope; report any dependent step as unavailable.


# cmux Control

## When to Use

- Use when you need to inspect, create, close, or rearrange cmux panes, surfaces, or workspaces.
- Use when you need to send input to or monitor agents running inside cmux.

cmux is a native macOS terminal app for running multiple AI coding agents in parallel. It exposes a CLI (`cmux`) and a Unix-socket JSON-RPC API (`/tmp/cmux.sock`) for full topology and browser control.

## Core Concepts

- **Window** — top-level macOS cmux window
- **Workspace** — sidebar tab within a window (one git branch / project context)
- **Pane** — split region inside a workspace
- **Surface** — tab inside a pane (terminal or browser)

Handles default to short refs (`workspace:2`, `pane:1`, `surface:7`); UUIDs accepted as input. Add `--id-format uuids|both` for UUID output.

### Ref syntax — get this right or fail silently

- **Always use PREFIXED refs** (`pane:38`, `surface:46`). A **bare number is treated as an INDEX, not an ID** — `--surface 46` means "the surface at index 46" (usually nonexistent → silent failure), NOT `surface:46`.
- **`read-screen` and `capture-pane` have NO `--pane` flag** — they target `--workspace` or `--surface` only. Passing `--pane` errors, and a bare/missing target falls back to your OWN surface (you'll read your own footer and draw wrong conclusions). To read a pane: resolve it to a surface FIRST with `cmux list-pane-surfaces --pane pane:N`, then `cmux read-screen --surface surface:N`.
- **Never append `2>/dev/null` to cmux commands.** Errors go to stderr with exit code 1; suppressing them blinds you to your own ref/flag mistakes (the #1 cause of "(no output)").

## Detect cmux in a Shell

```bash
[ -S "${CMUX_SOCKET_PATH:-/tmp/cmux.sock}" ] || exit 0   # bail if not in cmux
[ -n "${CMUX_WORKSPACE_ID:-}" ] && echo "inside cmux surface"
```

Injected env vars in every cmux-spawned terminal: `CMUX_WORKSPACE_ID`, `CMUX_SURFACE_ID`, `CMUX_SOCKET_PATH`, `CMUX_PORT`. **Always anchor automation to `CMUX_WORKSPACE_ID`** — the visually focused workspace may not be the agent's caller workspace.

## Fast Start — Topology

```bash
cmux identify --json                              # who am I (window/workspace/pane/surface)
cmux tree                                         # full hierarchy
cmux list-workspaces --json
cmux list-panes --workspace "$CMUX_WORKSPACE_ID"
cmux list-surfaces --workspace "$CMUX_WORKSPACE_ID"

cmux new-workspace --name "feature-x" --cwd /path/to/repo
cmux new-pane --workspace "$CMUX_WORKSPACE_ID" --type terminal --direction right --focus false
cmux new-pane --workspace "$CMUX_WORKSPACE_ID" --type browser  --direction right --url http://localhost:3000
cmux move-surface --surface surface:7 --pane pane:2 --focus false
cmux split-off --surface surface:7 right
cmux reorder-surface --surface surface:7 --before surface:3
cmux close-surface --surface surface:7
```

## Polling Pi Agents in Panes — Keep Sleeps Short

When launching a Pi Agent inside a cmux pane and polling for output, use **short `sleep` intervals (2–5s)**. Pi is fast and minimal, and the user runs it on Opus 4.8 Fast via OpenRouter, which streams tokens extremely quickly. Do NOT use `sleep 15` unless genuinely needed (a big build/refactor) — most of the time `sleep 2`–`sleep 5` is more than enough.

After every agent check, send the user a one-line status update: what the agent is doing and whether it is on track. Keep it extremely concise.

Claude Code cmux note: after Claude finishes, it may prefill a predicted next user message; that draft is Claude, not the user speaking.

## Send Input

**Command names:** there is NO `send-surface` / `send-key-surface`. Target a specific surface with the `--surface` flag on `send` / `send-key` (same commands as the focused terminal). `send-panel` / `send-key-panel` exist ONLY for panels (`--panel`), not surfaces.

```bash
cmux send "echo hi\n"                                       # focused terminal
cmux send-key "ctrl+c"                                       # enter|tab|esc|backspace|arrows|ctrl+x|shift+tab
cmux send --surface surface:7 "npm run build"               # specific surface (NOT send-surface)
cmux send-key --surface surface:7 enter                     # specific surface (NOT send-key-surface)
```

## Notifications & Sidebar Metadata

```bash
cmux notify --title "Done" --body "tests passed"
cmux set-status build "compiling" --icon hammer --color "#ff9500"
cmux set-progress 0.5 --label "Building..."
cmux log --level success "All 42 tests passed"               # info|progress|success|warning|error
cmux trigger-flash --workspace "$CMUX_WORKSPACE_ID"          # blue-ring attention cue
cmux sidebar-state --json                                    # dump all sidebar metadata
```

## Browser Automation (WKWebView)

Workflow: open → wait → snapshot → act → re-snapshot.

```bash
S=$(cmux --json browser open https://example.com | jq -r .result.surface_ref)
cmux browser "$S" wait --load-state complete --timeout-ms 15000
cmux browser "$S" snapshot --interactive                     # returns elements as e1, e2, ...
cmux browser "$S" fill e1 "<email-address>"
cmux browser "$S" click e2 --snapshot-after

# Navigation / inspection
cmux browser "$S" goto URL | back | forward | reload
cmux browser "$S" get url | get title | get text body | get value "#email" | get count ".row"
cmux browser "$S" eval 'return document.title'

# Waits
cmux browser "$S" wait --selector "#ready" --timeout-ms 10000
cmux browser "$S" wait --url-contains "/dashboard" --timeout-ms 10000

# Session
cmux browser "$S" cookies get | cookies set --name foo --value bar
cmux browser "$S" state save /tmp/auth.json | state load /tmp/auth.json

# Diagnostics
cmux browser "$S" console list | errors list | screenshot
```

**Not supported by WKWebView** (return `not_supported`): viewport emulation, geolocation/offline emulation, trace recording, network route interception, raw input injection.

## Markdown Viewer

```bash
cmux markdown open plan.md --direction right                 # live-watching renderer
cmux open file.pdf                                           # auto-routes to right viewer
```

`cmux markdown open` flags: `--workspace`, `--surface`, `--window`, `--direction <right|down|left|up>`, `--focus <true|false>`. There is **NO `--pane` flag** — passing it errors. To target a pane, pass `--surface <existing-md-surface-in-that-pane>`.

### Reuse the existing right markdown pane (don't spawn strays)

Default behavior of `markdown open` is to **create a new pane** every time, even with `--direction right`. To keep all docs as tabs in ONE right pane, follow this exactly:

```bash
# 1. Find the right pane and its surfaces (anchor to THIS workspace)
cmux list-panes --workspace "$CMUX_WORKSPACE_ID"
cmux list-pane-surfaces --pane pane:10        # the right/helper pane

# 2. Open targeting an existing markdown surface IN that pane (reuses pane, adds tab)
cmux markdown open /abs/path/file.md --surface surface:12 --focus false

# 3. If it STILL spawned a new pane (it can), move the new surface in + verify
cmux move-surface --surface surface:NEW --pane pane:10 --focus false
cmux list-panes --workspace "$CMUX_WORKSPACE_ID"   # confirm stray pane is gone
```

### Swapping the file in the single right pane (close-FIRST, then open)

To replace the doc shown in your one right markdown pane, the ONLY reliable order is **close the previous surface FIRST, then `markdown open` the new file fresh** — never move an existing viewer, never open-then-close.

```bash
# 1. close the previous right markdown surface (right side goes empty)
cmux list-panes --workspace "$CMUX_WORKSPACE_ID"
cmux close-surface --surface surface:PREV
# 2. THEN open the new file fresh
cmux markdown open /abs/path/new.md --direction right --focus false
```

ORDER MATTERS: close-previous BEFORE open-new. Opening first then closing the old one, or `move-surface`-ing an existing viewer, leaves the right pane BLANK.

### Hard-won lessons (avoid the trial-and-error)

- **Surface refs are global, not per-workspace.** A ref like `surface:126` from an earlier `markdown open` may live in a different window/workspace. Always re-list (`list-panes` / `list-pane-surfaces`) before reusing a ref — never assume a ref from a previous turn is still in the right pane.
- **`move-surface`-ing a markdown viewer often leaves it BLANK.** The moved surface keeps `type=markdown` and `surface-health` looks fine, but renders nothing. Fix: `close-surface` it and `cmux markdown open <path>` fresh, then move the *fresh* surface if needed. Don't waste time on `refresh-surfaces` — it usually won't fix a moved-then-blank viewer.
- **You cannot screenshot or `read-screen` a markdown surface** (`Surface is not a terminal` / browser screenshot is WKWebView-only). To verify a markdown viewer rendered, ask the user or open the file in a browser surface instead. Don't burn turns trying to capture it.
- **`cmux list-surfaces` does not exist.** Use `cmux list-pane-surfaces [--pane ...]`.

## Settings & Config

```bash
cmux docs settings        # prints paths, schema URL, reload cmd — read BEFORE editing
cmux settings path        # path to cmux.json
cmux settings cmux-json   # open in editor
cmux reload-config        # hot-reload cmux.json + ~/.config/ghostty/config (Cmd+Shift+,)
```

Locations:
- cmux settings: `~/.config/cmux/cmux.json` (canonical). Project-local override: `.cmux/cmux.json` or `./cmux.json`.
- Terminal rendering (font, cursor, theme, scrollback, opacity, blur): `~/.config/ghostty/config` — NOT cmux.json.

Before editing `cmux.json`, copy it to a timestamped `.bak` next to it so the user can revert. Schema: `https://raw.githubusercontent.com/manaflow-ai/cmux/main/web/data/cmux.schema.json`.

## Agent Hooks & Install

```bash
brew tap manaflow-ai/cmux && brew install --cask cmux
sudo ln -sf /Applications/cmux.app/Contents/Resources/bin/cmux /usr/local/bin/cmux
cmux hooks setup                                             # all detected agents
cmux hooks setup codex|grok|antigravity|opencode             # specific agent
npx skills add manaflow-ai/cmux -g -y                        # install cmux skills for agents
```

Native session-resume supported for: Claude Code, Codex, Grok, OpenCode, Pi, Amp, Cursor CLI, Gemini, Antigravity, Rovo Dev, Hermes, Copilot, CodeBuddy, Factory, Qoder.

## Socket API (advanced)

`/tmp/cmux.sock` — Unix socket, JSON-RPC v2. Use for tight loops where subprocess spawn cost matters; otherwise prefer the CLI.

```bash
echo '{"id":"1","method":"workspace.list","params":{}}' | nc -U /tmp/cmux.sock
```

Method prefixes: `system.*`, `window.*`, `workspace.*`, `pane.*`, `surface.*`, `notification.*`, `browser.*`. Full list and Python client example in `references/socket-api.md`.

Access modes: `cmuxOnly` (default — only cmux-spawned processes), `automation` (any local process), `password`, `allowAll` (unsafe). If you hit `Failed to connect to socket`, you're likely an external process under `cmuxOnly` — switch mode in Settings > Automation or run from inside a cmux terminal.

## Critical Rules — Non-Disruptive Automation

These rules come from the `cmux-workspace` skill and prevent agents from yanking the user's focus:

1. **Anchor to `CMUX_WORKSPACE_ID`.** Never assume the visually focused workspace is the target.
2. **Never call focus-changing verbs speculatively.** `select-workspace`, `focus-pane`, `focus-panel`, `focus-surface` only on explicit user request. Pass `--focus false` whenever available.
3. **Build layout additively in one call.** `cmux new-pane --type … --focus false` beats create-then-move-then-focus chains.
4. **Right-side helper pane pattern.** Reuse an existing non-caller helper pane if present; otherwise create exactly one right-side pane.
5. **Never send input to surfaces you don't own.** Only target surfaces in the caller's workspace unless the user explicitly asks for cross-workspace routing.
6. **Check surface health before routing input** when UI state may be stale: `cmux surface-health`.

## Common Pitfalls

- **Pi/Pi-like socket connection failures from external processes** → default `cmuxOnly` mode; either run inside a cmux terminal or change socket mode.
- **macOS only.** No Linux/Windows port.
- **WKWebView ≠ CDP.** Don't expect Playwright-equivalent network mocking or viewport emulation.
- **Resume strips sensitive env vars.** Re-inject tokens at resume time if the agent needs them.
- **Skills snapshot at app start.** Edits to skill files require a restart of the consuming agent.
- **Legacy v1 socket payloads (`{"command":...}`) rejected.** Use v2 JSON-RPC only.
- **Don't `cat ~/.cmuxterm/*-hook-sessions.json`** expecting secrets — they're scrubbed. Look there for session/surface mappings only.

## Reference: Full CLI Help

For any command, `cmux <cmd> --help` is authoritative. Use `cmux capabilities --json` to enumerate available socket methods in the current build.

## Keyboard Shortcuts (most-used)

Workspaces: ⌘N new, ⌘1–8 jump, ⌃⌘[ / ⌃⌘] prev/next, ⌘⇧W close, ⌘B sidebar.
Surfaces: ⌘T new, ⌘⇧[ / ⌘⇧] prev/next, ⌘W close, ⌃1–8 jump.
Splits: ⌘D right, ⌘⇧D down, ⌥⌘D browser right, ⌥⌘←→↑↓ focus directional, ⌘⇧↵ zoom.
Browser: ⌘⇧L open, ⌘L address bar, ⌘[/⌘] back/forward, ⌥⌘I devtools.
App: ⌘, settings, ⌘⇧, reload-config, ⌘⇧P palette, ⌘⇧O restore session, ⌃⌥⌘. system-wide show/hide.

## Limitations

- Adapted from `davidondrej/skills`; verify local paths, tools, credentials, and agent features before acting.
- For commands, remote access, scheduling, browser automation, or file-changing workflows, get explicit user approval and confirm the target environment first.