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.

``bash 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 ``

1. 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.
2. Back up the target file when it already exists (applicable path only, no backup for a missing file).

``bash 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 ``

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

``bash ~/.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 ``

1. 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).
2. cmux reload-config.
3. 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](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.