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Plugins
Hermes has a plugin system for adding custom tools, hooks, slash commands, and integrations without modifying core code.
→ Build a Hermes Plugin — step-by-step guide with a complete working example.
Quick overview
Drop a directory into ~/.hermes/plugins/ with a plugin.yaml and Python code:
~/.hermes/plugins/my-plugin/
├── plugin.yaml # manifest
├── __init__.py # register() — wires schemas to handlers
├── schemas.py # tool schemas (what the LLM sees)
└── tools.py # tool handlers (what runs when called)
Start Hermes — your tools appear alongside built-in tools. The model can call them immediately.
Project-local plugins under ./.hermes/plugins/ are disabled by default. Enable them only for trusted repositories by setting HERMES_ENABLE_PROJECT_PLUGINS=true before starting Hermes.
What plugins can do
| Capability | How |
|---|---|
| Add tools | ctx.register_tool(name, schema, handler) |
| Add hooks | ctx.register_hook("post_tool_call", callback) |
| Add slash commands | ctx.register_command("mycommand", handler) |
| Ship data files | Path(__file__).parent / "data" / "file.yaml" |
| Bundle skills | Copy skill.md to ~/.hermes/skills/ at load time |
| Gate on env vars | requires_env: [API_KEY] in plugin.yaml |
| Distribute via pip | [project.entry-points."hermes_agent.plugins"] |
Plugin discovery
| Source | Path | Use case |
|---|---|---|
| User | ~/.hermes/plugins/ |
Personal plugins |
| Project | .hermes/plugins/ |
Project-specific plugins (requires HERMES_ENABLE_PROJECT_PLUGINS=true) |
| pip | hermes_agent.plugins entry_points |
Distributed packages |
Available hooks
Plugins can register callbacks for these lifecycle events. See the Event Hooks page for full details, callback signatures, and examples.
| Hook | Fires when |
|---|---|
pre_tool_call |
Before any tool executes |
post_tool_call |
After any tool returns |
pre_llm_call |
Before LLM API request (planned) |
post_llm_call |
After LLM API response (planned) |
on_session_start |
Session begins (planned) |
on_session_end |
Session ends (planned) |
Slash commands
Plugins can register slash commands that work in both CLI and messaging platforms:
def register(ctx):
ctx.register_command(
name="greet",
handler=lambda args: f"Hello, {args or 'world'}!",
description="Greet someone",
args_hint="[name]",
aliases=("hi",),
)
The handler receives the argument string (everything after /greet) and returns a string to display. Registered commands automatically appear in /help, tab autocomplete, Telegram bot menu, and Slack subcommand mapping.
| Parameter | Description |
|---|---|
name |
Command name without slash |
handler |
Callable that takes args: str and returns `str |
description |
Shown in /help |
args_hint |
Usage hint, e.g. "[name]" |
aliases |
Tuple of alternative names |
cli_only |
Only available in CLI |
gateway_only |
Only available in messaging platforms |
Managing plugins
/plugins # list loaded plugins in a session
hermes config set display.show_cost true # show cost in status bar
See the full guide for handler contracts, schema format, hook behavior, error handling, and common mistakes.