# Plugins: add tools and lifecycle behavior

> Extend Hermes with custom tools, hooks, and integrations when instructions alone cannot supply the needed capability.

Canonical: https://hermeswatcher.com/tools/plugins  
Kind: Capability · Development & operations  
Last reviewed: Oct 19, 2026  
Basis: Explained from the official Hermes Agent docs and repository (Nous Research). Steps follow the linked official sources.

## What it is for

A plugin is useful when the missing piece is executable behavior: a tool that calls an internal service, a lifecycle hook that records an event, or an integration shared by a team. Official documentation describes a manifest and Python registration code, separate from modifications to the Hermes core. Choose this route only after checking whether an existing tool, skill, or MCP server already solves the problem.

## What you need

- A maintained Hermes installation whose plugin API matches the plugin documentation.
- A trusted plugin source, declared dependencies, and an explicit description of data access and external effects.

## Setting it up

1. Define one narrow capability and its input/output contract. Decide which actions are read-only and which require additional authorization.
2. Develop against the official example in an isolated profile. Keep credentials outside source code and document an enable/disable and rollback procedure.

## How to check it works

- Confirm that the expected tool is registered, run one harmless example, and inspect both the returned data and any external side effects.
- Exercise a missing credential or invalid input and verify that it fails clearly without silently expanding permissions.

## Limits

- A plugin can run code; a descriptive manifest is not a security boundary.
- Compatibility and dependency maintenance belong to the plugin operator. Documentation support does not mean every third-party plugin is verified or interchangeable.

## Related workflows

- [Know whether an automation actually worked](https://hermeswatcher.com/workflows/reliable-recurring-automation.md)
- [Build a useful GitHub issue review](https://hermeswatcher.com/workflows/github-issue-review.md)

## Sources

- [Official plugin system](https://hermes-agent.nousresearch.com/docs/user-guide/features/plugins)

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HermesWatcher is an independent guide. It is not affiliated with or endorsed by Nous Research. The [official Hermes Agent documentation](https://hermes-agent.nousresearch.com/docs) and [repository](https://github.com/NousResearch/hermes-agent) from Nous Research are the authority; each page here lists the official sources it was written from. If this site and the official docs disagree, trust the official docs. Index for agents: https://hermeswatcher.com/llms.txt