website/docs/developer-guide/extending-the-cli.md

metadata

sidebar_position: 8
title: Extending the CLI
description: >-
  Build wrapper CLIs that extend the Hermes TUI with custom widgets,
  keybindings, and layout changes

Extending the CLI

Hermes exposes protected extension hooks on HermesCLI so wrapper CLIs can add widgets, keybindings, and layout customizations without overriding the 1000+ line run() method. This keeps your extension decoupled from internal changes.

Extension points

There are five extension seams available:

Hook	Purpose	Override when...
_get_extra_tui_widgets()	Inject widgets into the layout	You need a persistent UI element (panel, status line, mini-player)
_register_extra_tui_keybindings(kb, *, input_area)	Add keyboard shortcuts	You need hotkeys (toggle panels, transport controls, modal shortcuts)
_build_tui_layout_children(**widgets)	Full control over widget ordering	You need to reorder or wrap existing widgets (rare)
process_command()	Add custom slash commands	You need /mycommand handling (pre-existing hook)
_build_tui_style_dict()	Custom prompt_toolkit styles	You need custom colors or styling (pre-existing hook)

The first three are new protected hooks. The last two already existed.

Quick start: a wrapper CLI

#!/usr/bin/env python3
"""my_cli.py — Example wrapper CLI that extends Hermes."""

from cli import HermesCLI
from prompt_toolkit.layout import FormattedTextControl, Window
from prompt_toolkit.filters import Condition


class MyCLI(HermesCLI):

    def __init__(self, **kwargs):
        super().__init__(**kwargs)
        self._panel_visible = False

    def _get_extra_tui_widgets(self):
        """Add a toggleable info panel above the status bar."""
        cli_ref = self
        return [
            Window(
                FormattedTextControl(lambda: "📊 My custom panel content"),
                height=1,
                filter=Condition(lambda: cli_ref._panel_visible),
            ),
        ]

    def _register_extra_tui_keybindings(self, kb, *, input_area):
        """F2 toggles the custom panel."""
        cli_ref = self

        @kb.add("f2")
        def _toggle_panel(event):
            cli_ref._panel_visible = not cli_ref._panel_visible

    def process_command(self, cmd: str) -> bool:
        """Add a /panel slash command."""
        if cmd.strip().lower() == "/panel":
            self._panel_visible = not self._panel_visible
            state = "visible" if self._panel_visible else "hidden"
            print(f"Panel is now {state}")
            return True
        return super().process_command(cmd)


if __name__ == "__main__":
    cli = MyCLI()
    cli.run()

Run it:

cd ~/.hermes/hermes-agent
source .venv/bin/activate
python my_cli.py

Hook reference

_get_extra_tui_widgets()

Returns a list of prompt_toolkit widgets to insert into the TUI layout. Widgets appear between the spacer and the status bar — above the input area but below the main output.

def _get_extra_tui_widgets(self) -> list:
    return []  # default: no extra widgets

Each widget should be a prompt_toolkit container (e.g., Window, ConditionalContainer, HSplit). Use ConditionalContainer or filter=Condition(...) to make widgets toggleable.

from prompt_toolkit.layout import ConditionalContainer, Window, FormattedTextControl
from prompt_toolkit.filters import Condition

def _get_extra_tui_widgets(self):
    return [
        ConditionalContainer(
            Window(FormattedTextControl("Status: connected"), height=1),
            filter=Condition(lambda: self._show_status),
        ),
    ]

_register_extra_tui_keybindings(kb, *, input_area)

Called after Hermes registers its own keybindings and before the layout is built. Add your keybindings to kb.

def _register_extra_tui_keybindings(self, kb, *, input_area):
    pass  # default: no extra keybindings

Parameters:

• kb — The KeyBindings instance for the prompt_toolkit application
• input_area — The main TextArea widget, if you need to read or manipulate user input

def _register_extra_tui_keybindings(self, kb, *, input_area):
    cli_ref = self

    @kb.add("f3")
    def _clear_input(event):
        input_area.text = ""

    @kb.add("f4")
    def _insert_template(event):
        input_area.text = "/search "

Avoid conflicts with built-in keybindings: Enter (submit), Escape Enter (newline), Ctrl-C (interrupt), Ctrl-D (exit), Tab (auto-suggest accept). Function keys F2+ and Ctrl-combinations are generally safe.

_build_tui_layout_children(**widgets)

Override this only when you need full control over widget ordering. Most extensions should use _get_extra_tui_widgets() instead.

def _build_tui_layout_children(self, *, sudo_widget, secret_widget,
    approval_widget, clarify_widget, spinner_widget, spacer,
    status_bar, input_rule_top, image_bar, input_area,
    input_rule_bot, voice_status_bar, completions_menu) -> list:

The default implementation returns:

[
    Window(height=0),       # anchor
    sudo_widget,            # sudo password prompt (conditional)
    secret_widget,          # secret input prompt (conditional)
    approval_widget,        # dangerous command approval (conditional)
    clarify_widget,         # clarify question UI (conditional)
    spinner_widget,         # thinking spinner (conditional)
    spacer,                 # fills remaining vertical space
    *self._get_extra_tui_widgets(),  # YOUR WIDGETS GO HERE
    status_bar,             # model/token/context status line
    input_rule_top,         # ─── border above input
    image_bar,              # attached images indicator
    input_area,             # user text input
    input_rule_bot,         # ─── border below input
    voice_status_bar,       # voice mode status (conditional)
    completions_menu,       # autocomplete dropdown
]

Layout diagram

The default layout from top to bottom:

1. Output area — scrolling conversation history
2. Spacer
3. Extra widgets — from _get_extra_tui_widgets()
4. Status bar — model, context %, elapsed time
5. Image bar — attached image count
6. Input area — user prompt
7. Voice status — recording indicator
8. Completions menu — autocomplete suggestions

Tips

• Invalidate the display after state changes: call self._invalidate() to trigger a prompt_toolkit redraw.
• Access agent state: self.agent, self.model, self.conversation_history are all available.
• Custom styles: Override _build_tui_style_dict() and add entries for your custom style classes.
• Slash commands: Override process_command(), handle your commands, and call super().process_command(cmd) for everything else.
• Don't override run() unless absolutely necessary — the extension hooks exist specifically to avoid that coupling.