Cmux Skill for Claude

cmux

Controls the cmux macOS terminal app via its CLI socket API to orchestrate workspaces, panes, browser previews, sidebar status, and notifications.

Full CLI reference: references/api_reference.md

Quick Check

Always verify cmux is running before issuing commands:

cmux ping 2>/dev/null && echo "ok" || echo "cmux not available"

If unavailable, skip cmux enhancements silently — never block the main task.

Core Use Cases

1. Auto Preview Routing

When a dev server starts or an HTML file is created, open it in a right-side browser pane:

# Dev server detected (e.g. localhost:3000)
cmux new-pane --type browser --direction right --url http://localhost:3000

# HTML file created — serve it first, then preview
cd <project-dir> && python3 -m http.server 8080 &
cmux new-pane --type browser --direction right --url http://localhost:8080/<file>.html

When to trigger:

• Output contains localhost:PORT, 127.0.0.1:PORT, Server running, Listening on
• A .html file is written and the user would benefit from seeing it rendered
• superpowers or another skill opens a visual artifact

Direction heuristic: right for wide layouts, down for narrow/tall terminals.

2. Subagent Workspaces

When dispatching parallel agents (via superpowers:dispatching-parallel-agents or similar), give each agent its own named cmux workspace so it's visible in the sidebar:

# Create a workspace per agent (new-workspace has no --cwd — cd inside --command)
cmux new-workspace --command "cd /path/to/project && claude --dangerously-skip-permissions"
cmux rename-workspace "agent: fix-auth"

# Set status so the sidebar shows what the agent is doing
cmux set-status task "fix-auth" --icon "⚡"
cmux set-status state "running" --color "#F59E0B"

When an agent completes:

cmux notify --title "Agent done" --subtitle "fix-auth" --body "Merged and cleaned up"
cmux set-status state "done" --color "#10B981"

Pattern: workspace 1 = orchestrator, workspaces 2–8 = subagents. Use cmux list-workspaces --json to track IDs.

3. Sidebar Status & Progress

Show live feedback for long-running tasks without interrupting the main session:

# Task start
cmux set-progress 0 --label "Building..."
cmux set-status phase "build" --icon "🔨"

# Midpoint update
cmux set-progress 0.5 --label "Running tests..."
cmux set-status phase "test" --icon "🧪"

# Completion
cmux set-progress 1 --label "Done"
cmux notify --title "Task complete" --body "All tests passed"
cmux clear-progress

Use cmux log <message> --level info to append entries to the workspace log panel (visible via ⌘I).

When to use: any task taking >10 seconds — file processing, test runs, builds, research sweeps, code generation loops.

4. Utility Splits on Demand

Open any content in a split pane in the requested direction:

# Open a URL in a browser split
cmux new-pane --type browser --direction right --url <url>

# Open a terminal split running a command (e.g. log tail)
cmux new-pane --type terminal --direction down
cmux send "tail -f /path/to/server.log"
cmux send-key "Enter"

# Resize to make it a narrow utility strip
cmux resize-pane --pane <id> -D --amount 20   # shrink height by 20 rows

Direction mapping for natural language:

| User says | Direction flag |

|---|---|

| "on the right" / "beside" | --direction right |

| "on the left" | --direction left |

| "below" / "at the bottom" | --direction down |

| "above" / "at the top" | --direction up |

| "in a new tab" / "new workspace" | cmux new-workspace |

5. Workspace & Tab Actions

workspace-action and tab-action expose the right-click context-menu actions.

Full table with flags in references/api_reference.md — the available action names are:

cmux workspace-action --action <name> (sidebar workspaces):

pin · unpin · rename (needs --title) · clear-name · move-up · move-down ·

move-top · mark-read · mark-unread · close-others · close-above · close-below

cmux tab-action --action <name> (horizontal tabs):

rename · clear-name · pin · unpin · reload · duplicate ·

new-terminal-right · new-browser-right · mark-read · mark-unread ·

close-left · close-right · close-others

> ⚠️ Destructive actions act on OTHER tabs, not the one you name.

> close-others / close-above / close-below (workspace) and

> close-left / close-right / close-others (tab) close everything *except* the

> target. close-others spares pinned workspaces only. Never run these to

> "test" — they will close the user's live tabs. Prefer close-workspace --workspace <id>

> to close one specific workspace.

Renaming / selecting (common gotchas):

• Rename the sidebar/switcher label → cmux workspace-action --action rename --title "<name>"

(or cmux rename-workspace <name>). rename-tab only renames an inner tab and does

not change the switcher label.

• Select/focus a workspace → cmux select-workspace --workspace <id>. There is no

--action select (it errors "Unknown workspace action").

When unsure of a command's exact flags, run cmux <command> --help — every command

embeds full usage.

Combining Use Cases

Full workflow example — superpowers runs a subagent that builds a UI:

# 1. Announce work in sidebar
cmux set-progress 0 --label "Scaffolding UI..."
cmux set-status agent "ui-builder" --icon "🎨"

# 2. Subagent does its work...

# 3. Server starts → auto-preview
cmux new-pane --type browser --direction right --url http://localhost:5173

# 4. Mark done
cmux set-progress 1 --label "Preview ready"
cmux notify --title "UI ready" --body "Preview open on the right"
cmux clear-progress

Demo Mode (/cmux demo)

When invoked as /cmux demo, run an interactive personalized walkthrough. Always verify cmux ping first — abort with a clear message if unavailable.

Screen 1 — Workflow

Ask with AskUserQuestion:

question: "What best describes how you work?"
header: "Workflow"
options:
  - label: "Coding agent manager"
    description: "Running multiple Claude sessions in parallel"
  - label: "Web dev"
    description: "Browser preview, dev servers, HTML artifacts"
  - label: "Research / long tasks"
    description: "Vault work, builds, sweeps that take minutes"
  - label: "Show me everything"
    description: "Run all demos back to back"

Screen 2 — Mode

question: "How do you want to explore?"
header: "Demo mode"
options:
  - label: "Walk me through it"
    description: "Step by step with explanations between each demo"
  - label: "Auto-run"
    description: "Run all relevant demos back to back, narrate as you go"
  - label: "Just the commands"
    description: "Show what you'd run, skip execution"

Screen 3 — tmux

question: "Do you use tmux?"
header: "tmux"
options:
  - label: "Yes, daily"
    description: "Show me the cmux + tmux combo"
  - label: "For SSH / remote only"
    description: "Show the remote persistence pattern"
  - label: "Not really"
    description: "Skip tmux, focus on cmux-native features"

Demo Catalog

Run demos based on Screen 1 answer. Each demo: announce what's happening, execute the commands, narrate what the user is seeing, suggest what to try next.

A — Browser preview pane (web dev, show everything)

• Create /tmp/cmux-preview.html with a minimal styled page
• python3 -m http.server <PORT> --directory /tmp &
• cmux new-pane --type browser --direction right --url http://localhost:<PORT>/cmux-preview.html
• Use cmux browser --surface <id> screenshot to show the rendered result inline
• Suggest: "Try editing the HTML — navigate the browser pane to reload"

B — Sidebar progress (research / long tasks, show everything)

• Animate through 0→0.3→0.7→1.0 with label changes (set-progress, set-status)
• Fire cmux notify on completion
• cmux log a few entries, mention ⌘I to open the log panel
• Suggest: "Watch this sidebar during your next vault scan or research sweep"

C — Subagent workspaces (coding agent manager, show everything)

• cmux new-workspace --command "echo 'agent: fix-auth'" + rename
• cmux set-status with agent name + color
• cmux notify simulating completion
• cmux close-workspace cleanup
• Suggest: "Next time you run parallel agents via /dispatching-parallel-agents, this happens automatically"

D — tmux inside cmux (if Screen 3 = daily or SSH)

• cmux new-pane --type terminal --direction right
• cmux send --surface <id> "tmux new-session -s work\n"
• Build 2–3 named windows (editor, server, git)
• Capture with cmux read-screen --surface <id> and show output
• Suggest: "tmux keeps the session alive if cmux restarts. Use tmux attach -t work to reconnect."

E — Utility split on demand (all workflows)

• cmux new-pane --type terminal --direction down
• Send a tail -f or git log --follow -p command into it
• cmux resize-pane -D --amount 10 to shrink it to a strip
• Suggest: "Say 'open a log strip at the bottom' during any task and this happens automatically"

Auto mode

In auto mode (Screen 2 = "Auto-run"):

• Run all demos relevant to Screen 1 without pausing for confirmation
• Use cmux set-progress and cmux set-status to show overall demo progress in the sidebar
• Narrate each step in text as it executes
• At the end: print a summary of what ran and key shortcuts to remember

Cleanup

After each demo (or at the end of auto mode), close any panes/workspaces/processes created:

cmux close-surface --surface <id>   # or close-workspace
kill <server-pid>
cmux clear-progress
cmux clear-status <key>

Error Handling

• If cmux ping fails: skip all cmux calls, proceed with task normally
• If a new-pane or new-workspace call fails: log a warning, don't retry
• Never let cmux failures block or slow down the main task
• In demo mode: if a command fails, explain what should have happened and move on