Plugins

Hermes has a plugin system for adding custom tools, hooks, and integrations without modifying core code.

If you want to create a custom tool for yourself, your team, or one project, this is usually the right path. The developer guide's Adding Tools page is for built-in Hermes core tools that live in tools/ and toolsets.py.

→ Build a Hermes Plugin — step-by-step guide with a complete working example.

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.

Minimal working example

Here is a complete plugin that adds a hello_world tool and logs every tool call via a hook.

~/.hermes/plugins/hello-world/plugin.yaml

name: hello-world
version: "1.0"
description: A minimal example plugin

~/.hermes/plugins/hello-world/__init__.py

"""Minimal Hermes plugin — registers a tool and a hook."""




def register(ctx):
    # --- Tool: hello_world ---
    schema = {
        "name": "hello_world",
        "description": "Returns a friendly greeting for the given name.",
        "parameters": {
            "type": "object",
            "properties": {
                "name": {
                    "type": "string",
                    "description": "Name to greet",
                }
            },
            "required": ["name"],
        },
    }

    def handle_hello(params, **kwargs):
        del kwargs
        name = params.get("name", "World")
        return json.dumps({"success": True, "greeting": f"Hello, {name}!"})

    ctx.register_tool(
        name="hello_world",
        toolset="hello_world",
        schema=schema,
        handler=handle_hello,
    )

    # --- Hook: log every tool call ---
    def on_tool_call(tool_name, params, result):
        print(f"[hello-world] tool called: {tool_name}")

    ctx.register_hook("post_tool_call", on_tool_call)

Drop both files into ~/.hermes/plugins/hello-world/, restart Hermes, and the model can immediately call hello_world. The hook prints a log line after every tool invocation.

The model-facing tool description belongs in schema["description"]. The optional ctx.register_tool(description=...) value is separate ToolEntry registry metadata: when omitted, it defaults to the schema description, but Hermes does not copy it back into a schema that lacks description. Prefer defining the text once in the schema. If you provide both values, keep them synchronized; the model sees the schema value.

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.

Every ctx.* API below is available inside a plugin's register(ctx) function.

Later sources override earlier ones on name collision, so a user plugin with the same name as a bundled plugin replaces it.

Plugin sub-categories

Within each source, Hermes also recognizes sub-category directories that route plugins to specialized discovery systems:

User plugins at ~/.hermes/plugins/model-providers/<name>/ and ~/.hermes/plugins/memory/<name>/ override bundled plugins of the same name — last-writer-wins in register_provider() / register_memory_provider(). Drop a directory in, and it replaces the built-in without any repo edits.

General plugins and user-installed backends are disabled by default — discovery finds them (so they show up in hermes plugins and /plugins), but nothing with hooks or tools loads until you add the plugin's name to plugins.enabled in ~/.hermes/config.yaml. This stops third-party code from running without your explicit consent.

plugins:
  enabled:
    - my-tool-plugin
    - disk-cleanup
  disabled:       # optional deny-list — always wins if a name appears in both
    - noisy-plugin

Three ways to flip state:

hermes plugins                    # interactive toggle (space to check/uncheck)
hermes plugins enable <name>      # add to allow-list
hermes plugins disable <name>     # remove from allow-list + add to disabled

After hermes plugins install owner/repo, you're asked Enable 'name' now? [y/N] — defaults to no. Skip the prompt for scripted installs with --enable or --no-enable.

For a reproducible install, pin a full immutable commit (tags, branches, and abbreviated SHAs are not accepted):

hermes plugins install owner/repo --ref 0123456789abcdef0123456789abcdef01234567

Hermes checks out the commit detached, verifies that HEAD exactly matches the requested SHA, and records the canonical source, installed revision, and pin status in the current profile. hermes plugins update refuses to move a pinned plugin; choose a new exact commit explicitly with hermes plugins install <source> --force --ref <new-commit>. The profile-local install metadata contains no config values, environment values, secrets, or capability grants.

What the allow-list does NOT gate

Several categories of plugin bypass plugins.enabled — they're part of Hermes' built-in surface and would break basic functionality if gated off by default:

In short: bundled "always-works" infrastructure loads automatically; third-party general plugins are opt-in. The plugins.enabled allow-list is the gate specifically for arbitrary code a user drops into ~/.hermes/plugins/.

Approval transports

An approval transport changes where a human sees and answers an existing Hermes tool-approval request. It does not decide whether a command needs approval and it is not an authorization-policy API.

def present(request):
    # Deliver request.command and request.description to your UI, wait for
    # its authenticated human response, then return a request-bound decision.
    choice = send_to_my_ui_and_wait(request)  # once/session/always/deny
    return request.respond(choice)


def register(ctx):
    ctx.register_approval_transport("my-ui", present)

present may be synchronous or async. Hermes runs it on a bounded worker and enforces the canonical approvals.timeout even if the plugin does not. The request is immutable and contains redacted display text, its host presentation class (cli or gateway), the host timeout, allowed choices, and an opaque request ID/digest. Return the result of request.respond(choice); unbound dictionaries and stale or changed request IDs/digests are rejected. A plugin cannot return a scope that the host did not offer (for example, always on a once-only request).

Registration alone does nothing. Enabling the plugin and explicitly selecting its transport are separate consent steps:

plugins:
  enabled: [my-approval-plugin]

security:
  approval:
    transport: my-ui
    transport_fallback: deny     # default

Transport exceptions, timeouts, unavailable registrations, invalid choices, and stale responses deny by default. To deliberately show the prompt on the ordinary CLI/TUI/gateway/ACP surface when the selected transport fails, set transport_fallback: builtin. Without that exact opt-in, Hermes never materializes the prompt on another surface.

Hermes still owns hardline blocks, sudo-stdin protection, user deny rules, request binding, allowed scopes, persistence, hooks, and final authorization. Hardline commands are blocked before any transport callback. There is intentionally **no plugin approval policy, auto-allow callback, or required pre_tool_call policy** in this interface. A future approval-policy capability may use the plugin capability-consent model, but transport selection does not grant it.

Migration for existing users

When you upgrade to a version of Hermes that has opt-in plugins (config schema v21+), any user plugins already installed under ~/.hermes/plugins/ that weren't already in plugins.disabled are automatically grandfathered into plugins.enabled. Your existing setup keeps working. Bundled standalone plugins are NOT grandfathered — even existing users have to opt in explicitly. (Bundled platform/backend plugins never needed grandfathering because they were never gated.)

Plugins can register the 26 lifecycle events currently accepted by hermes_cli.plugins.VALID_HOOKS. The Event Hooks catalog is canonical for exact timing, return handling, payload fields, and privacy notes.

These categories describe current behavior rather than defining future naming rules. Plugin middleware remains a separate registry/surface.

Hermes has four kinds of plugins:

Memory providers and context engines are provider plugins — only one of each type can be active at a time. Model providers are also plugins, but many load simultaneously; the user picks one at a time via --provider or config.yaml. General plugins can be enabled in any combination.

The table above shows the four plugin categories, but within "General plugins" the PluginContext exposes several distinct extension points — and Hermes also accepts extensions outside the Python plugin system (config-driven backends, shell-hooked commands, external servers, etc.). Use this table to find the right doc for what you want to build:

On NixOS, plugins can be installed declaratively via the module options — no hermes plugins install needed. See the Nix Setup guide for full details.

services.hermes-agent = {
  # Directory plugin (source tree with plugin.yaml)
  extraPlugins = [ (pkgs.fetchFromGitHub { ... }) ];
  # Entry-point plugin (pip package)
  extraPythonPackages = [ (pkgs.python312Packages.buildPythonPackage { ... }) ];
  # Enable in config
  settings.plugins.enabled = [ "my-plugin" ];
};

Declarative plugins are symlinked with a nix-managed- prefix — they coexist with manually installed plugins and are cleaned up automatically when removed from the Nix config.

hermes plugins                               # unified interactive UI
hermes plugins list                          # table: enabled / disabled / not enabled
hermes plugins search <term>                 # search the community plugin index
hermes plugins install <name>                # install by index name (resolved to repo @ pinned ref)
hermes plugins install user/repo             # install from Git, then prompt Enable? [y/N]
hermes plugins install user/repo --enable    # install AND enable (no prompt)
hermes plugins install user/repo --no-enable # install but leave disabled (no prompt)
hermes plugins update my-plugin              # pull latest (local edits are autostashed and re-applied)
hermes plugins remove my-plugin              # uninstall
hermes plugins enable my-plugin              # add to allow-list
hermes plugins disable my-plugin             # remove from allow-list + add to disabled
hermes plugins capabilities [my-plugin]      # declared vs granted capabilities

Plugin capabilities and consent

Plugins can declare the privileged host surfaces they want in their plugin.yaml:

name: my-plugin
capabilities:
  - tools.override        # replace built-in tools
  - llm.model_override    # pick the model for host-owned LLM calls

When a plugin declares capabilities, hermes plugins install (and hermes plugins enable) shows the list with one-line risk descriptions and asks once. Consenting records the grant under plugins.entries.<id>.granted_capabilities together with a consent hash and timestamp. Declining leaves the plugin enabled with those capabilities off — a well-behaved plugin probes with ctx.has_capability() and degrades gracefully.

Update re-consent: if a plugin update declares capabilities you haven't granted, hermes plugins update surfaces the additions and asks again. New capabilities stay off until you consent — a plugin update can never silently widen its access.

Non-interactive sessions fail closed: installing or updating without a TTY completes the install, but declared capabilities are not granted. Run hermes plugins enable <id> interactively to grant them later.

Inspect the state at any time:

hermes plugins capabilities             # all plugins with declared/granted capabilities
hermes plugins capabilities my-plugin   # one plugin, declared vs granted

Capability ids map 1:1 to the older per-feature config gates, which keep working but are deprecated in favor of the consent flow:

A gate is open when either the capability is granted or the legacy key is set — existing configs keep working unchanged.

Platform actions

ctx.platform_actions gives a plugin a minimal, capability-gated verb set for acting on connected chat platforms through the live gateway adapter registry — the sanctioned alternative to monkeypatching an adapter. **It is off by default**: every call re-checks the gateway.platform_actions capability (legacy key plugins.entries.<id>.allow_platform_actions), and an ungranted call returns a structured error instead of acting.

v1 verbs (both async, both return a plain dict, and neither ever raises into hook dispatch):

result = await ctx.platform_actions.add_reaction(
    platform="telegram", chat_id="-100123", message_id="456", emoji="👍",
)
result = await ctx.platform_actions.set_thread_title(
    platform="discord", chat_id="123", thread_id="456", title="New title",
)
if not result["ok"]:
    print(result["error"], result.get("detail"))

Success is {"ok": True, "action": <verb>}. Failures are {"ok": False, "error": <code>, "detail": <str>} with stable error codes: capability_not_granted, invalid_argument, gateway_unavailable, unknown_platform, adapter_not_registered, adapter_disconnected, unsupported_platform_action, action_failed. Actions validate that the target adapter exists and is connected before acting; a disconnected or missing adapter degrades to a structured error, never an exception.

Platforms supported in v1: Telegram and Discord. Telegram's add_reaction sets the bot's reaction (the Bot API replaces a previous bot reaction rather than stacking). Every action — allowed or denied — is written to the log with the plugin id, verb, platform, and outcome.

Discovering community plugins

hermes plugins search <term> searches the community plugin index — a static, machine-readable JSON catalog of community plugins. Matching is fuzzy across name, description, and tags:

hermes plugins search telegram               # fuzzy search
hermes plugins search                        # browse the whole index
hermes plugins search --capability platform  # filter by declared capability
hermes plugins search media --json           # machine-readable output
hermes plugins search --refresh              # bypass the 24h local cache

Once you've found a plugin, install it by bare name — the name is resolved through the index to its owner/repo plus the index-pinned commit:

hermes plugins install hermes-media-studio

If a name matches more than one entry, the candidates are listed and nothing is installed. Explicit owner/repo or Git-URL identifiers never touch the index and keep working exactly as before. An explicit --ref <sha> always overrides the index pin.

How the index is fetched. The index lives at a canonical URL (https://raw.githubusercontent.com/NousResearch/hermes-plugin-index/main/index.json, overridable via hermes config set plugins.index_url <url>). Fetches are cached under ~/.hermes/cache/plugin_index.json for 24 hours; when the remote is unreachable the stale cache is used, and when there is no cache at all a bundled seed copy ships with Hermes — so search works fully offline.

Index entry format. Each entry is a JSON object:

{
  "name": "hermes-media-studio",
  "description": "Generative media workspace plugin.",
  "author": "NousResearch",
  "tags": ["media", "image-gen"],
  "repo": "NousResearch/hermes-media-studio",
  "ref": "<40-char commit SHA>",
  "subdir": null,
  "homepage": "https://github.com/NousResearch/hermes-media-studio",
  "capabilities": ["tools", "dashboard"],
  "api_version": 1,
  "added_at": "2026-08-12"
}

repo is the owner/name GitHub identifier, ref pins an immutable commit SHA, and optional subdir supports monorepos. The bundled seed file (hermes_cli/data/plugin_index.json in the repo) is the format reference.

Submitting a plugin. The index is maintained as a plain JSON file — submit a pull request to the hermes-plugin-index ↗ repository adding your entry (name, description, author, tags, owner/repo, and a pinned commit SHA). Review covers the entry's metadata only.

Plugin packs

A plugin pack is a declarative, shareable YAML file (hermes-pack.yaml) that pins a set of plugins — like sharing a modpack. Installing a pack fans out to ordinary pinned installs; nothing new exists at runtime.

name: voice-assistant-pack
description: STT + streaming TTS + approval relay
author: hyper
version: 1.0.0
plugins:
  - name: hermes-media-studio            # bare community-index name…
    ref: e8d59971d2b7901405b39dac7b03bdd616272d0d
  - repo: owner/approval-relay           # …or explicit owner/repo (or git URL)
    ref: 8f3c2d1a9b4e5f6071829304a5b6c7d8e9f00112
    subdir: plugins/relay                # optional monorepo path
config:                                  # optional, non-secret seeds only
  hermes-media-studio:
    default_model: flux-3
skills: []                               # declared list only (not auto-installed yet)

hermes plugins pack show ./hermes-pack.yaml     # dry-run review
hermes plugins pack install ./hermes-pack.yaml  # review → confirm → install
hermes plugins pack export > hermes-pack.yaml   # snapshot the current install
hermes plugins pack export --enabled-only       # only plugins.enabled

Supply-chain posture. Every entry's ref must be an exact 40-character commit SHA — tags and branch names are rejected with an error naming the entry, the same rule as the community index. Pack installs ride the exact same pinned install path as hermes plugins install --ref <sha> and record the same provenance in plugins/.install-metadata.json, so two installs of the same pack resolve identically. Packs build on the manifest v2 fields (manifest_version, api_version, requires_plugins) — each plugin's own manifest still validates through the normal install path.

Consent is never bulk-granted. pack install shows a mandatory review screen (every plugin, source, pinned ref, and the capabilities it declares), then asks one confirmation for the pack contents. After that, each plugin's declared capabilities go through the standard per-plugin capability-consent prompt — identical to a single hermes plugins install. There is no --yes, and non-interactive sessions cannot install packs.

Secrets never travel in packs. config: seeds are limited to non-secret plugins.entries.<id> keys — secret-shaped key names (*token*, *key*, *password*, …), capability grants, and the deprecated allow_* trust gates are rejected on install and stripped on export. Plugins that need secrets declare them in their own requires_env, which prompts during install as usual. Existing user values in plugins.entries.<id> always win over pack seeds.

Partial failure. Each plugin installs independently; failures are reported per plugin, the rest continue, and the command exits non-zero if any plugin failed.

Export caveats. pack export only includes plugins with known Git provenance (installed via hermes plugins install). Local-only plugins are listed as warning comments in the emitted YAML, not as installable entries.

The skills: list is parsed and displayed at install time but not yet auto-installed — install those manually for now (hermes skills). Wiring skill-hub ids into pack install is a documented follow-up seam.

Install-time security scanning

Every hermes plugins install and hermes plugins update runs a static security scan over the plugin tree before it is activated (inspired by Claude Cowork's skill & plugin security scanning). The scanner reuses the same threat-pattern engine as the Skills Hub guard — exfiltration of credential stores, reverse shells, destructive commands, persistence mechanisms, obfuscated execution, and prompt injection in documentation files — with plugin-aware exemptions: a provider plugin reading its own API key from the environment (the documented requires_env pattern) is not flagged.

Three verdicts, matching Cowork's pass/warn/fail:

On hermes plugins update, a dangerous verdict on the updated tree disables the plugin until you review the findings and re-enable it.

Scanning is on by default; disable it in config.yaml:

plugins:
  scan_on_install: false

Interactive UI

Running hermes plugins with no arguments opens a composite interactive screen:

Plugins
  ↑↓ navigate  SPACE toggle  ENTER configure/confirm  ESC done

  General Plugins
 → [✓] my-tool-plugin — Custom search tool
   [ ] webhook-notifier — Event hooks
   [ ] disk-cleanup — Auto-cleanup of ephemeral files [bundled]

  Provider Plugins
     Memory Provider          ▸ honcho
     Context Engine           ▸ compressor

• General Plugins section — checkboxes, toggle with SPACE. Checked = in plugins.enabled, unchecked = in plugins.disabled (explicit off).
• Provider Plugins section — shows current selection. Press ENTER to drill into a radio picker where you choose one active provider.
• Bundled plugins appear in the same list with a [bundled] tag.

Provider plugin selections are saved to config.yaml:

memory:
  provider: "honcho"      # empty string = built-in only

context:
  engine: "compressor"    # default built-in compressor

Enabled vs. disabled vs. neither

Plugins occupy one of three states:

The default for a newly-installed or bundled plugin is not enabled. hermes plugins list shows all three distinct states so you can tell what's been explicitly turned off vs. what's just waiting to be enabled.

In a running session, /plugins shows which plugins are currently loaded.

Plugins can inject messages into a CLI conversation or a known gateway session using ctx.inject_message():

# Active CLI conversation
ctx.inject_message("New data arrived from the webhook", role="user")

# Existing gateway conversation
ctx.inject_message(
    "New data arrived from the webhook",
    role="user",
    session_key="agent:main:telegram:dm:123456789",
)

Signature: ctx.inject_message(content: str, role: str = "user", *, session_key: str | None = None) -> bool

In CLI mode:

• If the agent is idle (waiting for user input), the message is queued as the next input and starts a new turn.
• If the agent is mid-turn (actively running), the message interrupts the current operation — the same as a user typing a new message and pressing Enter.
• For non-"user" roles, the content is prefixed with [role] (e.g. [system] ...).
• Returns True if the message was queued successfully.

In gateway mode:

• session_key is required and must identify an existing gateway session. It is the stable routing key, not the CLI session ID.
• Hermes reuses that session's stored platform, chat, thread, profile, and conversation history. Plugins cannot supply a new chat route through this API.
• Hermes rechecks the stored route against the gateway's current authorisation rules before dispatch.
• Routes that relied only on an adapter-time or upstream authorisation decision are rejected unless Hermes can revalidate them from current core allowlists, pairing, or explicit allow-all configuration.
• Injected text is always conversational input. It cannot invoke slash commands, approve tools, or resolve pending confirmation and clarification prompts.
• The route and conversation are pinned while dispatch is pending. Hermes drops the request if topic recovery changes the route or the session rotates before handling starts.
• The request enters the platform adapter's normal message path. Active sessions use the existing busy-session queue rather than starting a competing turn.
• Returns True when the live gateway accepts the request for asynchronous dispatch. This does not confirm that the agent turn or platform delivery has completed.
• Returns False when session_key is omitted, the permission is not granted, or no live gateway can accept the request. Unknown or unroutable session keys discovered after asynchronous acceptance are written to the gateway log.

This enables plugins like remote control viewers, messaging bridges, or webhook receivers to feed messages into the conversation from external sources.

Gateway injection can send an agent response to an external messaging platform. It is disabled by default for every plugin. Grant it per plugin in config.yaml:

plugins:
  entries:
    my-plugin:
      allow_gateway_injection: true

ctx.call_mcp() lets a plugin call a tool on one of the user's configured MCP servers — synchronously, from any hook or tool handler — routing through Hermes' existing native MCP client (same connections, trust-tier gates, circuit breaker, and reconnect logic as model-invoked MCP tools; never a parallel client).

result = ctx.call_mcp(
    "knowledge_rag",            # server name from mcp.servers
    "query_knowledge",          # tool on that server
    {"query": "deploy runbook"},
    timeout=30,                 # seconds; clamped to 1–600
)
if result["ok"]:
    print(result["result"])
else:
    print("MCP error:", result["error"])

Signature: ctx.call_mcp(server: str, tool: str, arguments: dict | None = None, timeout: float = 30) -> dict

Returns a stable envelope: {"ok": True, "result": ...} (plus structuredContent when the server provides it) or {"ok": False, "error": "..."}. Results over ~64 KB are truncated and flagged with "truncated": True.

Security: default-off, per-server allowlist

A plugin has no MCP access by default. The operator must grant each server explicitly in config.yaml:

plugins:
  entries:
    my-plugin:
      mcp_allowlist: ["knowledge_rag", "github"]

• Calling a server not in the list raises PermissionError naming the exact config key to set.
• The grant is per-server and per-plugin — never ambient authority over every configured server, and "*" wildcards are not honored.
• Every call has an enforced timeout (default 30 s) so a hung MCP server cannot stall the hook or tool pipeline that invoked it.
• MCP servers return untrusted content. Treat result as data, not instructions — don't feed it into privileged decisions (approvals, command execution) without validation.

See the full guide for handler contracts, schema format, hook behavior, error handling, and common mistakes.