/customizing-commands

name: customizing-commands
description: Creates, edits, and enables Letta Code mod-provided slash commands. Use when the user asks to add a custom /command, slash command, command shortcut, scoped conversation-backed command, or command-driven panel behavior.

Customizing Commands

Use this as the command-specific entrypoint for local mod slash commands. For broader mod work, recipes live in `../creating-mods/references/commands.md`, `../creating-mods/references/architecture.md`, `../creating-mods/references/ui.md`, and `../creating-mods/references/plan-mode.md`.

Mod files live in:

~/.letta/mods/

Use a focused file name, e.g. `~/.letta/mods/review.ts` or `~/.letta/mods/commands.ts`.

First decide whether a command is right

| User wants | Build | | --- | --- | | `/foo` sends a prompt or shows local output | Mod command | | `/foo` starts a reusable agent workflow | Skill + thin mod command | | Agent/model should autonomously call the capability | Mod tool, not a command | | Command shows transient progress/results | Mod command + panel | | Command needs model output while the main agent is busy | `runWhenBusy: true` command + forked `ctx.conversation` |

If the command is a reusable workflow like `/goal`, put the workflow instructions in a skill and keep the mod command as a small launcher/prompt.

Workflow

1. Inspect `~/.letta/mods/` for related command files. 2. Preserve unrelated mod code; create a focused new file if merging is messy. 3. Register with `letta.commands.register()` and guard with `letta.capabilities.commands`. 4. Return the unregister function, or a disposer that calls it plus any timer/panel cleanup. 5. Tell the user the exact file path changed and to run `/reload`.

Default prompt command

export default function activate(letta) {
  if (!letta.capabilities.commands) return;

  return letta.commands.register({
    id: "review",
    description: "Review current git changes",
    args: "[focus]",
    run(ctx) {
      const focus = ctx.args.trim();
      return {
        type: "prompt",
        content: focus
          ? `Review current git changes. Focus on ${focus}.`
          : "Review current git changes. Focus on correctness issues.",
        systemReminder: true,
      };
    },
  });
}

Command result types

type ModCommandResult =
  | { type: "prompt"; content: string; systemReminder?: boolean }
  | { type: "output"; output: string; success?: boolean }
  | { type: "handled" };

• `prompt`: sends content to the agent. Use for normal slash shortcuts.
• `output`: prints local text and does not contact the agent.
• `handled`: command handled its own side effects/UI; common for panel commands.

Rules

• Command IDs omit the slash: `id: "review"`, not `"/review"`.
• Use lowercase slugs with letters, numbers, and hyphens.
• Do not register built-in command IDs.
• `runWhenBusy: true` commands must not return `prompt` while the main agent is busy; use scoped conversation helpers/panels and return `handled`.
• `showInTranscript: false` commands should usually return `handled`, not `prompt`.
• Do not import Letta Code app internals.
• Do not do surprising side effects on startup; mods activate on app start and `/reload`.

More recipes

• Simple output command, panel command, busy-safe conversation command: `../creating-mods/references/commands.md`
• Complex command architecture, state, cleanup: `../creating-mods/references/architecture.md`
• Panel/status UI patterns: `../creating-mods/references/ui.md`
• Worked plan-mode command/tool composition: `../creating-mods/references/plan-mode.md`