> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://docs.nvidia.com/nemo/relay/llms.txt.
> For full documentation content, see https://docs.nvidia.com/nemo/relay/llms-full.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://docs.nvidia.com/nemo/relay/_mcp/server.

# Hermes Agent

Use this guide to observe local Hermes Agent sessions with NeMo Relay through
Hermes shell hooks and the `nemo-relay` gateway.

Hermes shell hooks provide session, subagent, tool, and LLM lifecycle events.
For NeMo Relay contract work, `pre_api_request`, `post_api_request`, and
`api_request_error` are the authoritative LLM lifecycle hooks. The legacy
`pre_llm_call` and `post_llm_call` hooks still exist, but only as private
hint-style signals. Complete LLM request and response observability still
requires model traffic to route through the gateway.

## Transparent Run

Use the wrapper when you want the gateway lifetime managed for a local Hermes
process:

```bash
nemo-relay hermes
```

Pass Hermes arguments after `--`:

```bash
nemo-relay hermes -- chat --provider custom
```

Once NeMo Relay config exists, this shortcut is equivalent to
`nemo-relay run --agent hermes`. The wrapper starts a gateway on a dynamic
`127.0.0.1` port and exports `NEMO_RELAY_GATEWAY_URL` for the launched
process. After initial NeMo Relay setup exists, Hermes hook configuration is
temporary in this mode: the launcher merges the NeMo Relay hook-forward
commands into the configured Hermes hook file for the run and restores the
original file afterward. The wrapper also sets `HERMES_ACCEPT_HOOKS=1` so
Hermes can use the injected hook commands without extra manual approval
prompts.

If no NeMo Relay config exists yet, `nemo-relay hermes` triggers the setup flow
first and then launches Hermes through the same wrapped pipeline.

Inspect what would be launched without starting Hermes:

```bash
nemo-relay run \
  --dry-run \
  --print \
  -- hermes
```

## Shared Config

Create `.nemo-relay/config.toml` for project defaults or
`~/.config/nemo-relay/config.toml` for user defaults:

```toml
[agents.hermes]
command = "hermes"
```

Then configure observability with `nemo-relay plugins edit --project` or
`.nemo-relay/plugins.toml`:

```toml
version = 1

[[components]]
kind = "observability"
enabled = true

[components.config.atif]
enabled = true
output_directory = ".nemo-relay/atif"

[components.config.openinference]
enabled = true
endpoint = "http://127.0.0.1:4318/v1/traces"
```

Run `nemo-relay run --agent hermes` to use the configured command and plugin
config. User config takes priority over project and system config.

## Hermes Hook Setup

Unlike the other agents, Hermes reads hooks from `.hermes/config.yaml`. The
setup wizard writes that file for you when you select hermes — running
`nemo-relay config` (or `nemo-relay config hermes` to scope to one agent) merges
NeMo Relay hook commands into the YAML, preserving any existing config, and
records the path under `[agents.hermes].hooks_path` in `.nemo-relay/config.toml`.

The generated Hermes hooks cover `on_session_start`, `on_session_end`,
`on_session_finalize`, `on_session_reset`, `pre_llm_call`, `post_llm_call`,
`pre_api_request`, `post_api_request`, `api_request_error`, `pre_tool_call`,
`post_tool_call`, `subagent_start`, and `subagent_stop`.

The API hooks are the main Hermes LLM lifecycle path for NeMo Relay. The legacy
LLM hooks remain installed because they can still provide useful private hints,
but they are not treated as equal peers to the API hooks in the observability
contract.

Hermes hook forwarding prefers `NEMO_RELAY_GATEWAY_URL` when set (this is what
`nemo-relay hermes` injects on every run). When launched outside the wrapper —
e.g., bare `hermes` against a long-running gateway — the hook command falls
back to `--gateway-url http://127.0.0.1:4040`.

For standalone gateway mode, start the daemon manually:

```bash
nemo-relay --bind 127.0.0.1:4040
```

Then point Hermes provider traffic at `http://127.0.0.1:4040` for any provider
mode that exposes a local OpenAI-compatible or Anthropic-compatible base URL.
This is the practical routed-provider validation path today.

Important distinction:

* Wrapped execution is the authoritative path for Hermes hook-path validation.
* Wrapped execution does not automatically rewrite Hermes provider `base_url`,
  `custom_providers`, or `api_mode`.
* Routed `/v1/messages`, `/v1/chat/completions`, or `/v1/responses` validation
  therefore requires explicit Hermes provider configuration in addition to the
  wrapped or standalone gateway.

## Smoke Test

Run a small Hermes session that starts, invokes one tool, and exits. Then check
hook forwarding directly:

```bash
curl -f http://127.0.0.1:4040/healthz
printf '{"session_id":"smoke-hermes","hook_event_name":"on_session_start"}' \
  | NEMO_RELAY_GATEWAY_URL=http://127.0.0.1:4040 nemo-relay hook-forward hermes --fail-closed
```

The response should be `{}`. If Hermes prompts for hook consent, approve the
NeMo Relay hook command interactively or through Hermes configuration before
relying on unattended capture.

## Verify Export

End a Hermes turn or finalize the session and confirm Agent Trajectory
Interchange Format (ATIF) exists:

```bash
ls .nemo-relay/atif
```

The gateway writes or updates an ATIF snapshot when it receives
`on_session_end`, `on_session_finalize`, or `on_session_reset`.
`on_session_end` is a per-turn snapshot boundary: it does not close the NeMo
Relay session and does not emit a visible trajectory mark. `on_session_finalize`
and `on_session_reset` close the session.

## Troubleshoot LLM Lifecycle

If hook events appear but LLM spans are missing, Hermes model traffic is not
routed through the gateway. If LLM spans exist but attach to the top-level agent
instead of a subagent, include shared identifiers in Hermes hook payloads and
gateway requests, such as `conversation_id`, `generation_id`, `request_id`, or
`x-nemo-relay-subagent-id`.