cmux Customization

What it does

When your agent uses it

• Adding a custom action or command palette entry to cmux
• Replacing the new workspace button's behavior or right-click menu
• Setting up a dock with test watchers and dev server logs
• Sharing a team workspace layout through a project .cmux folder

Example prompts

• “Add a cmux action that opens a worktree with a terminal and a browser preview side by side.”
• “Change the plus button so a right-click offers my three workspace presets.”
• “Create a dock.json with a test watcher and a dev server log.”
• “Back up my cmux config and then change the terminal theme through Ghostty.”

Requirements

• cmux installed, with its cmux.json configuration

Workflow steps

7 steps, taken from the first numbered list in SKILL.md.

1. 1Inspect existing config before editing.
2. 2Pick global or project-local scope. Ask only when the choice changes behavior meaningfully. Default to project-local for repo-specific…
3. 3Before editing, back up the target file when it already exists
4. 4For app settings and cmux-owned shortcuts, use the settings helper from the installed skill or checkout
5. 5For actions, UI wiring, workspace layouts, notification hooks, and Dock controls, edit JSONC or JSON carefully. Preserve unrelated…
6. 6Reload config after successful edits
7. 7Verify the configured entrypoint exists. For shortcuts, read back the binding. For custom actions, confirm the action ID and where it…

What it can do on your machine

Read from SKILL.md and the folder at commit 6eaacab. It shows what the files ask for, not the result of running them.

• Tool permissions

  Pre-approves nothing: there is no allowed-tools line, so your agent's usual permission prompts apply.

  From allowed-tools in the SKILL.md frontmatter.

• Runs code

  No scripts in the folder and no shell commands in SKILL.md (its code samples are json and bash).

  From the folder's file list and the shell code blocks in SKILL.md.

• Network

  No URLs in SKILL.md.

  From URLs in SKILL.md, links to its own repository left out.

• Credentials

  Names no API keys, tokens, secrets or passwords.

  From names ending in _API_KEY, _TOKEN, _SECRET, _KEY or _PASSWORD in SKILL.md.

Context cost

cmux Customization loads about 2.4k tokens when it runs, and up to ~4.5k if it reads all its reference files. Until then it costs about 86 tokens; SKILL.md has 822 words of instructions outside code blocks.

Always · name and description, kept in context so the agent knows when to use it

~86

When it runs · the whole SKILL.md, loaded when a task matches

~2.4k

With references · SKILL.md plus every file in references/, read only if the agent opens them

~4.5k

Estimates: characters ÷ 4, the usual rule of thumb; real counts depend on the model's tokenizer. Scripts and assets cost tokens only if the agent reads them.

Safety

Automated static check — not a guarantee. Review scripts before installing. It scans the text of SKILL.md for risky patterns (piping downloads into a shell, reading credential files, hidden Unicode, destructive commands); files beside SKILL.md are not scanned.

SKILL.md

The full file from disler/learning-cmux-with-agents at commit 6eaacab, republished under its MIT licence (© disler). 822 words, ~2,446 tokens.

name

cmux-customization

description

Customize cmux for an end user. Use when changing cmux.json actions, custom commands, workspace layouts, plus-button behavior, surface tab bar buttons, Command Palette entries, Dock controls, sidebar and app settings, shortcuts, notifications, browser routing, examples-library presets, or Ghostty-backed terminal preferences.

{
  "actions": {
    "codex-new-tab": {
      "type": "agent",
      "agent": "codex",
      "title": "Codex",
      "subtitle": "Start Codex in this workspace",
      "target": "newTabInCurrentPane",
      "palette": true
    }
  }
}

{
  "actions": {
    "worktree-agents": {
      "type": "workspaceCommand",
      "title": "Worktree Agents",
      "commandName": "Worktree Agents",
      "icon": { "type": "symbol", "name": "folder.badge.plus" }
    }
  },
  "ui": {
    "newWorkspace": {
      "action": "worktree-agents",
      "contextMenu": [
        { "action": "worktree-agents", "title": "Worktree Agents" },
        { "type": "separator" },
        { "action": "cmux.newTerminal", "title": "New Terminal" },
        { "action": "cmux.newBrowser", "title": "New Browser" }
      ]
    }
  },
  "commands": [
    {
      "name": "Worktree Agents",
      "description": "Create a worktree and open agents inside it",
      "workspace": {
        "name": "Worktree Agents",
        "cwd": "../worktrees/my-feature",
        "layout": {
          "direction": "horizontal",
          "children": [
            {
              "pane": {
                "surfaces": [
                  { "type": "terminal", "name": "Codex", "command": "codex" }
                ]
              }
            },
            {
              "pane": {
                "surfaces": [
                  { "type": "terminal", "name": "SSH", "command": "ssh devbox" }
                ]
              }
            }
          ]
        }
      }
    }
  ]
}

{
  "commands": [
    {
      "name": "dev",
      "workspace": {
        "name": "Dev",
        "cwd": ".",
        "layout": {
          "direction": "horizontal",
          "children": [
            { "pane": { "surfaces": [{ "type": "terminal", "command": "bun dev" }] } },
            { "pane": { "surfaces": [{ "type": "browser", "url": "http://localhost:3000" }] } }
          ]
        }
      }
    }
  ]
}

{
  "ui": {
    "surfaceTabBar": {
      "buttons": [
        "cmux.newTerminal",
        "cmux.newBrowser",
        {
          "action": "codex-new-tab",
          "title": "Codex",
          "icon": { "type": "symbol", "name": "terminal" }
        }
      ]
    }
  }
}

{
  "controls": [
    {
      "id": "git",
      "title": "Git",
      "command": "lazygit",
      "cwd": ".",
      "height": 300
    },
    {
      "id": "feed",
      "title": "Feed",
      "command": "cmux feed tui --opentui",
      "height": 260
    }
  ]
}

© disler, MIT. Rendered from Markdown: HTML in the file is shown as text, images as links, and headings moved down two levels. Raw file

Files

SKILL.md and 2 other files (references) in ai_docs/cmux-skills/cmux-customization of disler/learning-cmux-with-agents.

• SKILL.md
• agents/openai.yaml
• references/examples.md

Open the folder on GitHubat commit 6eaacab