97990e7ad5
Plugin system for extending Hermes with custom tools, hooks, and
integrations — no source code changes required.
Core system (hermes_cli/plugins.py):
- Plugin discovery from ~/.hermes/plugins/, .hermes/plugins/, and
pip entry_points (hermes_agent.plugins group)
- PluginContext with register_tool() and register_hook()
- 6 lifecycle hooks: pre/post tool_call, pre/post llm_call,
on_session_start/end
- Namespace package handling for relative imports in plugins
- Graceful error isolation — broken plugins never crash the agent
Integration (model_tools.py):
- Plugin discovery runs after built-in + MCP tools
- Plugin tools bypass toolset filter via get_plugin_tool_names()
- Pre/post tool call hooks fire in handle_function_call()
CLI:
- /plugins command shows loaded plugins, tool counts, status
- Added to COMMANDS dict for autocomplete
Docs:
- Getting started guide (build-a-hermes-plugin.md) — full tutorial
building a calculator plugin step by step
- Reference page (features/plugins.md) — quick overview + tables
- Covers: file structure, schemas, handlers, hooks, data files,
bundled skills, env var gating, pip distribution, common mistakes
Tests: 16 tests covering discovery, loading, hooks, tool visibility.
63 lines
2.1 KiB
Markdown
63 lines
2.1 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, 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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## 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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| 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 |
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| pip | `hermes_agent.plugins` entry_points | Distributed packages |
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## Available hooks
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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` | Before LLM API request |
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| `post_llm_call` | After LLM API response |
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| `on_session_start` | Session begins |
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| `on_session_end` | Session ends |
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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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