455bf2e853
The plugin system defined six lifecycle hooks but only pre_tool_call and
post_tool_call were invoked. This activates the remaining four so that
external plugins (e.g. memory systems) can hook into the conversation
loop without touching core code.
Hook semantics:
- on_session_start: fires once when a new session is created
- pre_llm_call: fires once per turn before the tool-calling loop;
plugins can return {"context": "..."} to inject into the ephemeral
system prompt (not cached, not persisted)
- post_llm_call: fires once per turn after the loop completes, with
user_message and assistant_response for sync/storage
- on_session_end: fires at the end of every run_conversation call
invoke_hook() now returns a list of non-None callback return values,
enabling pre_llm_call context injection while remaining backward
compatible (existing hooks that return None are unaffected).
Salvaged from PR #2823.
Co-authored-by: Nicolò Boschi <boschi1997@gmail.com>
96 lines
3.8 KiB
Markdown
96 lines
3.8 KiB
Markdown
---
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sidebar_position: 20
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---
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# Plugins
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Hermes has a plugin system for adding custom tools, hooks, slash commands, and integrations without modifying core code.
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**→ [Build a Hermes Plugin](/docs/guides/build-a-hermes-plugin)** — step-by-step guide with a complete working example.
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## Quick overview
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Drop a directory into `~/.hermes/plugins/` with a `plugin.yaml` and Python code:
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```
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~/.hermes/plugins/my-plugin/
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├── plugin.yaml # manifest
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├── __init__.py # register() — wires schemas to handlers
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├── schemas.py # tool schemas (what the LLM sees)
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└── tools.py # tool handlers (what runs when called)
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```
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Start Hermes — your tools appear alongside built-in tools. The model can call them immediately.
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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.
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## What plugins can do
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| Capability | How |
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|-----------|-----|
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| Add tools | `ctx.register_tool(name, schema, handler)` |
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| Add hooks | `ctx.register_hook("post_tool_call", callback)` |
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| Add slash commands | `ctx.register_command("mycommand", handler)` |
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| Ship data files | `Path(__file__).parent / "data" / "file.yaml"` |
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| Bundle skills | Copy `skill.md` to `~/.hermes/skills/` at load time |
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| Gate on env vars | `requires_env: [API_KEY]` in plugin.yaml |
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| Distribute via pip | `[project.entry-points."hermes_agent.plugins"]` |
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## Plugin discovery
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| Source | Path | Use case |
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|--------|------|----------|
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| User | `~/.hermes/plugins/` | Personal plugins |
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| Project | `.hermes/plugins/` | Project-specific plugins (requires `HERMES_ENABLE_PROJECT_PLUGINS=true`) |
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| pip | `hermes_agent.plugins` entry_points | Distributed packages |
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## Available hooks
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Plugins can register callbacks for these lifecycle events. See the **[Event Hooks page](/docs/user-guide/features/hooks#plugin-hooks)** for full details, callback signatures, and examples.
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| Hook | Fires when |
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|------|-----------|
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| `pre_tool_call` | Before any tool executes |
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| `post_tool_call` | After any tool returns |
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| `pre_llm_call` | Once per turn, before the LLM loop — can return `{"context": "..."}` to inject into the system prompt |
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| `post_llm_call` | Once per turn, after the LLM loop completes |
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| `on_session_start` | New session created (first turn only) |
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| `on_session_end` | End of every `run_conversation` call |
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## Slash commands
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Plugins can register slash commands that work in both CLI and messaging platforms:
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```python
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def register(ctx):
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ctx.register_command(
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name="greet",
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handler=lambda args: f"Hello, {args or 'world'}!",
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description="Greet someone",
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args_hint="[name]",
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aliases=("hi",),
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)
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```
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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.
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| Parameter | Description |
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|-----------|-------------|
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| `name` | Command name without slash |
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| `handler` | Callable that takes `args: str` and returns `str | None` |
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| `description` | Shown in `/help` |
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| `args_hint` | Usage hint, e.g. `"[name]"` |
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| `aliases` | Tuple of alternative names |
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| `cli_only` | Only available in CLI |
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| `gateway_only` | Only available in messaging platforms |
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| `gateway_config_gate` | Config dotpath (e.g. `"display.my_option"`). When set on a `cli_only` command, the command becomes available in the gateway if the config value is truthy. |
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## Managing plugins
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```
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/plugins # list loaded plugins in a session
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hermes config set display.show_cost true # show cost in status bar
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```
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See the **[full guide](/docs/guides/build-a-hermes-plugin)** for handler contracts, schema format, hook behavior, error handling, and common mistakes.
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