Cmux Customization

cmux Customization

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

For content viewers, start with the viewer customization matrix. It maps each viewer to the settings, command, or external file that owns its knobs, including explicit fallbacks for viewer types whose template settings have not shipped yet.

Choose the right surface

Viewer-specific JSON settings live in the global cmux.json: browser.*, markdown.*, fileEditor.*, fileExplorer.*, and diffViewer.*. Generic file preview routing also uses app.openSupportedFilesInCmux and app.openMarkdownInCmuxViewer plus app.preferredEditor. Right-sidebar tools are structural state and Dock configuration, not a templates.rightSidebarTool object.

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; copy built-ins cmux.copyWorkingDirectory, cmux.copyProjectRoot, and cmux.copyScreen also work here and in actions), and commands (workspace definitions with split layouts).

Workflow

1. Inspect existing config.

   bashCopy code
   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).

   bashCopy code
   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).

   bashCopy code
   ~/.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.

For viewer changes, verify the exact path or command state from the matrix. If the requested viewer or knob is absent from the schema, explain that it is not supported yet instead of writing an unknown key. The templates.<viewer> surface proposed for future notes/Markdown/diff customization is not available until the schema and runtime implement it.

Example: Command Palette action

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

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

Before choosing a preset, template, starter config, or known workflow pattern, run cmux docs workflows --json. Its catalog describes the shipped examples, what each creates, task-fit cues, requirements, adaptation points, and the saved-layout lifecycle. After choosing an example, open references/examples.md for that example's concrete JSON recipe.

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.