cmux Customization

Keep the user's config intact, prefer schema-backed edits, and validate before reporting completion.

Choose the right surface

Project-local .cmux/cmux.json and .cmux/dock.json let worktree, SSH, review, dev, CI, and docs patterns travel with the repo; project actions and commands override global entries with the same ID or name. Global app preferences do not belong there.

If a request can be handled by Ghostty config, say so and use Ghostty config instead of inventing cmux UI settings.

Key surfaces in cmux.json: actions (reusable, can appear in Cmd+Shift+P, surface tab bars, shortcuts, and the plus-button right-click menu), ui.newWorkspace.action (replaces the plus-button click) and ui.newWorkspace.contextMenu (right-click menu; ui.newWorkspace.rightClick is an accepted alias but new examples use contextMenu), ui.surfaceTabBar.buttons (replaces default tab bar buttons; include built-ins like cmux.newTerminal, cmux.newBrowser, cmux.splitRight, cmux.splitDown only when they should stay visible), and commands (workspace definitions with split layouts).

Workflow

1. Inspect existing config.

   test -f ~/.config/cmux/cmux.json && sed -n '1,220p' ~/.config/cmux/cmux.json
   test -f .cmux/cmux.json && sed -n '1,220p' .cmux/cmux.json
   

2. Pick global or project-local scope. Default to project-local for repo-specific commands, global for app preferences. Ask only when the choice changes behavior meaningfully.

3. Back up the target file when it already exists (applicable path only, no backup for a missing file).

   stamp="$(date +%Y%m%d-%H%M%S)"
   test -f ~/.config/cmux/cmux.json && cp -p ~/.config/cmux/cmux.json ~/.config/cmux/cmux.json."$stamp".bak
   test -f .cmux/cmux.json && cp -p .cmux/cmux.json .cmux/cmux.json."$stamp".bak
   

4. For app settings and cmux-owned shortcuts, use the settings helper (~/.codex/skills/... if the user installed with skills.sh).

   ~/.agents/skills/cmux-settings/scripts/cmux-settings list-supported
   ~/.agents/skills/cmux-settings/scripts/cmux-settings set browser.openTerminalLinksInCmuxBrowser true
   ~/.agents/skills/cmux-settings/scripts/cmux-settings validate
   

5. For actions, UI wiring, workspace layouts, notification hooks, and Dock controls, edit the JSONC by hand and preserve unrelated sections (vault, rightSidebar, commands, actions, ui, notifications).

6. cmux reload-config.

7. Verify the configured entrypoint exists: read back the shortcut binding, or confirm the action ID and where it should appear.

Example: Command Palette action

Appears in Cmd+Shift+P unless palette is false.

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

For worktree agents, full-stack dev layouts, SSH devboxes, PR review workspaces, docs workspaces, tab bar buttons, and CI watch Dock controls, read references/examples.md. Load it when the user asks for examples, presets, templates, starter configs, or a known workflow shape.

Validation

• App settings: cmux-settings validate.
• Keep valid JSONC, no duplicate keys.
• Parse .cmux/dock.json or ~/.config/cmux/dock.json with a JSON parser before reporting completion.
• cmux reload-config when the CLI is available.
• Confirm the exact user-facing result: action title, shortcut, plus-button behavior, context-menu entry, or tab bar placement.

Rules

• Do not overwrite a whole top-level config section unless you own the full section.
• Do not store secrets in actions, commands, or prompts. Use environment variables or the user's secret manager.
• Do not use sleeps or timing workarounds in generated commands.
• Do not add a cmux setting for behavior Ghostty already owns.
• Keep labels short enough for menus, buttons, and the Command Palette.