---
sidebar_position: 14
title: "API Server"
description: "Expose hermes-agent as an OpenAI-compatible API for any frontend"
---

# API Server

The API server exposes hermes-agent as an OpenAI-compatible HTTP endpoint. Any frontend that speaks the OpenAI format — Open WebUI, LobeChat, LibreChat, NextChat, ChatBox, and hundreds more — can connect to hermes-agent and use it as a backend.

Your agent handles requests with its full toolset (terminal, file operations, web search, memory, skills) and returns the final response. When streaming, tool progress indicators appear inline so frontends can show what the agent is doing.

:::tip One backend covers models + tools
Hermes itself needs a configured provider and tool backends for the API server to be useful. A [Nous Portal](/user-guide/features/tool-gateway) subscription handles both — 300+ models plus web/image/TTS/browser via the Tool Gateway. Run `hermes setup --portal` once before starting the API server and frontends like Open WebUI or LobeChat get a fully tool-equipped backend.
:::

## Quick Start

### 1. Enable the API server

Add to `~/.hermes/.env`:

```bash
API_SERVER_ENABLED=true
API_SERVER_KEY=change-me-local-dev
# Optional: only if a browser must call Hermes directly
# API_SERVER_CORS_ORIGINS=http://localhost:3000
```

### 2. Start the gateway

```bash
hermes gateway
```

You'll see:

```
[API Server] API server listening on http://127.0.0.1:8642
```

### 3. Connect a frontend

Point any OpenAI-compatible client at `http://localhost:8642/v1`:

```bash
# Test with curl
curl http://localhost:8642/v1/chat/completions \
  -H "Authorization: Bearer change-me-local-dev" \
  -H "Content-Type: application/json" \
  -d '{"model": "hermes-agent", "messages": [{"role": "user", "content": "Hello!"}]}'
```

Or connect Open WebUI, LobeChat, or any other frontend — see the [Open WebUI integration guide](/user-guide/messaging/open-webui) for step-by-step instructions.

## Endpoints

### POST /v1/chat/completions

Standard OpenAI Chat Completions format. Stateless — the full conversation is included in each request via the `messages` array.

**Request:**
```json
{
  "model": "hermes-agent",
  "messages": [
    {"role": "system", "content": "You are a Python expert."},
    {"role": "user", "content": "Write a fibonacci function"}
  ],
  "stream": false
}
```

**Response:**
```json
{
  "id": "chatcmpl-abc123",
  "object": "chat.completion",
  "created": 1710000000,
  "model": "hermes-agent",
  "choices": [{
    "index": 0,
    "message": {"role": "assistant", "content": "Here's a fibonacci function..."},
    "finish_reason": "stop"
  }],
  "usage": {"prompt_tokens": 50, "completion_tokens": 200, "total_tokens": 250}
}
```

**Inline image input:** user messages may send `content` as an array of `text` and `image_url` parts. Both remote `http(s)` URLs and `data:image/...` URLs are supported:

```json
{
  "model": "hermes-agent",
  "messages": [
    {
      "role": "user",
      "content": [
        {"type": "text", "text": "What is in this image?"},
        {"type": "image_url", "image_url": {"url": "https://example.com/cat.png", "detail": "high"}}
      ]
    }
  ]
}
```

Uploaded files (`file` / `input_file` / `file_id`) and non-image `data:` URLs return `400 unsupported_content_type`.

**Streaming** (`"stream": true`): Returns Server-Sent Events (SSE) with token-by-token response chunks. For **Chat Completions**, the stream uses standard `chat.completion.chunk` events plus Hermes' custom `hermes.tool.progress` event for tool-start UX. For **Responses**, the stream uses OpenAI Responses event types such as `response.created`, `response.output_text.delta`, `response.output_item.added`, `response.output_item.done`, and `response.completed`.

**Tool progress in streams**:
- **Chat Completions**: Hermes emits `event: hermes.tool.progress` for tool-start visibility without polluting persisted assistant text.
- **Responses**: Hermes emits spec-native `function_call` and `function_call_output` output items during the SSE stream, so clients can render structured tool UI in real time.

### POST /v1/responses

OpenAI Responses API format. Supports server-side conversation state via `previous_response_id` — the server stores full conversation history (including tool calls and results) so multi-turn context is preserved without the client managing it.

**Request:**
```json
{
  "model": "hermes-agent",
  "input": "What files are in my project?",
  "instructions": "You are a helpful coding assistant.",
  "store": true
}
```

**Response:**
```json
{
  "id": "resp_abc123",
  "object": "response",
  "status": "completed",
  "model": "hermes-agent",
  "output": [
    {"type": "function_call", "name": "terminal", "arguments": "{\"command\": \"ls\"}", "call_id": "call_1"},
    {"type": "function_call_output", "call_id": "call_1", "output": "README.md src/ tests/"},
    {"type": "message", "role": "assistant", "content": [{"type": "output_text", "text": "Your project has..."}]}
  ],
  "usage": {"input_tokens": 50, "output_tokens": 200, "total_tokens": 250}
}
```

**Inline image input:** `input[].content` can contain `input_text` and `input_image` parts. Both remote URLs and `data:image/...` URLs are supported:

```json
{
  "model": "hermes-agent",
  "input": [
    {
      "role": "user",
      "content": [
        {"type": "input_text", "text": "Describe this screenshot."},
        {"type": "input_image", "image_url": "data:image/png;base64,iVBORw0K..."}
      ]
    }
  ]
}
```

Uploaded files (`input_file` / `file_id`) and non-image `data:` URLs return `400 unsupported_content_type`.

#### Multi-turn with previous_response_id

Chain responses to maintain full context (including tool calls) across turns:

```json
{
  "input": "Now show me the README",
  "previous_response_id": "resp_abc123"
}
```

The server reconstructs the full conversation from the stored response chain — all previous tool calls and results are preserved. Chained requests also share the same session, so multi-turn conversations appear as a single entry in the dashboard and session history.

#### Named conversations

Use the `conversation` parameter instead of tracking response IDs:

```json
{"input": "Hello", "conversation": "my-project"}
{"input": "What's in src/?", "conversation": "my-project"}
{"input": "Run the tests", "conversation": "my-project"}
```

The server automatically chains to the latest response in that conversation. Like the `/title` command for gateway sessions.

### GET /v1/responses/\{id\}

Retrieve a previously stored response by ID.

### DELETE /v1/responses/\{id\}

Delete a stored response.

### GET /v1/models

Lists the agent as an available model. The advertised model name defaults to the [profile](/user-guide/profiles) name (or `hermes-agent` for the default profile). Required by most frontends for model discovery.

### GET /v1/capabilities

Returns a machine-readable description of the API server's stable surface for external UIs, orchestrators, and plugin bridges.

```json
{
  "object": "hermes.api_server.capabilities",
  "platform": "hermes-agent",
  "model": "hermes-agent",
  "auth": {"type": "bearer", "required": true},
  "features": {
    "chat_completions": true,
    "responses_api": true,
    "run_submission": true,
    "run_status": true,
    "run_events_sse": true,
    "run_stop": true
  }
}
```

Use this endpoint when integrating dashboards, browser UIs, or control planes so they can discover whether the running Hermes version supports runs, streaming, cancellation, and session continuity without depending on private Python internals.

### GET /health

Health check. Returns `{"status": "ok"}`. Also available at **GET /v1/health** for OpenAI-compatible clients that expect the `/v1/` prefix.

### GET /health/detailed

Extended health check that also reports active sessions, running agents, and resource usage. Useful for monitoring/observability tooling.

## Runs API (streaming-friendly alternative)

In addition to `/v1/chat/completions` and `/v1/responses`, the server exposes a **runs** API for long-form sessions where the client wants to subscribe to progress events instead of managing streaming themselves.

### POST /v1/runs

Create a new agent run. Returns a `run_id` that can be used to subscribe to progress events.

```json
{
  "run_id": "run_abc123",
  "status": "started"
}
```

Runs accept a simple `input` string and optional `session_id`, `instructions`, `conversation_history`, or `previous_response_id`. When `session_id` is provided, Hermes surfaces it in the run status so external UIs can correlate runs with their own conversation IDs.

### GET /v1/runs/\{run_id\}

Poll the current run state. This is useful for dashboards that need status without holding an SSE connection open, or for UIs that reconnect after navigation.

```json
{
  "object": "hermes.run",
  "run_id": "run_abc123",
  "status": "completed",
  "session_id": "space-session",
  "model": "hermes-agent",
  "output": "Done.",
  "usage": {"input_tokens": 50, "output_tokens": 200, "total_tokens": 250}
}
```

Statuses are retained briefly after terminal states (`completed`, `failed`, or `cancelled`) for polling and UI reconciliation.

### GET /v1/runs/\{run_id\}/events

Server-Sent Events stream of the run's tool-call progress, token deltas, and lifecycle events. Designed for dashboards and thick clients that want to attach/detach without losing state.

### POST /v1/runs/\{run_id\}/stop

Interrupt a running agent turn. The endpoint returns immediately with `{"status": "stopping"}` while Hermes asks the active agent to stop at the next safe interruption point.

### POST /v1/runs/\{run_id\}/approval

Resolve a pending approval for a run that is waiting on a human decision (for example, a tool call gated behind an approval policy). The body carries the approval decision; the run resumes once the decision is recorded. This endpoint is advertised in `/v1/capabilities` as the `run_approval` feature so external UIs can detect support before surfacing an approval prompt.

## Jobs API (background scheduled work)

The server exposes a lightweight jobs CRUD surface for managing scheduled / background agent runs from a remote client. All endpoints are gated behind the same bearer auth.

### GET /api/jobs

List all scheduled jobs.

### POST /api/jobs

Create a new scheduled job. Body accepts the same shape as `hermes cron` — prompt, schedule, skills, provider override, delivery target.

### GET /api/jobs/\{job_id\}

Fetch a single job's definition and last-run state.

### PATCH /api/jobs/\{job_id\}

Update fields on an existing job (prompt, schedule, etc.). Partial updates are merged.

### DELETE /api/jobs/\{job_id\}

Remove a job. Also cancels any in-flight run.

### POST /api/jobs/\{job_id\}/pause

Pause a job without deleting it. Next-scheduled-run timestamps are suspended until resumed.

### POST /api/jobs/\{job_id\}/resume

Resume a previously paused job.

### POST /api/jobs/\{job_id\}/run

Trigger the job to run immediately, out of schedule.

## Sessions API (session control over REST)

External UIs can manage Hermes sessions over REST without standing up the dashboard. All endpoints are gated by `API_SERVER_KEY` and live under `/api/sessions/*`.

| Method | Path | Description |
|--------|------|-------------|
| `GET` | `/api/sessions` | List sessions (paginated — `limit`, `offset`, `source`, `include_children`) |
| `POST` | `/api/sessions` | Create an empty session |
| `GET` | `/api/sessions/{id}` | Read session metadata |
| `PATCH` | `/api/sessions/{id}` | Update title or `end_reason` |
| `DELETE` | `/api/sessions/{id}` | Delete a session |
| `GET` | `/api/sessions/{id}/messages` | Message history for a session |
| `POST` | `/api/sessions/{id}/fork` | Branch the session via `SessionDB` lineage (matches CLI `/branch` semantics) |
| `POST` | `/api/sessions/{id}/chat` | Run one synchronous agent turn |
| `POST` | `/api/sessions/{id}/chat/stream` | SSE wrapper over a single turn — emits `assistant.delta`, `tool.started`, `tool.completed`, `run.completed` events |

`/v1/capabilities` advertises the full surface via `session_*` feature flags and `endpoints.session_*` entries so external UIs can detect support and fall back safely. Inline images are supported in `chat` and `chat/stream` payloads (multimodal-aware path).

```bash
# fork a session and run one turn
curl -X POST http://localhost:8642/api/sessions/$ID/fork \
  -H "Authorization: Bearer $API_SERVER_KEY" \
  -d '{"title": "explore alt path"}'

# stream a turn over SSE
curl -N -X POST http://localhost:8642/api/sessions/$ID/chat/stream \
  -H "Authorization: Bearer $API_SERVER_KEY" \
  -d '{"input": "what files changed in the last hour?"}'
```

## Skills and toolsets discovery

`GET /v1/skills` and `GET /v1/toolsets` let external clients enumerate the agent's capabilities deterministically over REST instead of asking the model. Both are read-only and gated by `API_SERVER_KEY`.

```bash
curl http://localhost:8642/v1/skills \
  -H "Authorization: Bearer $API_SERVER_KEY"
# → [{"name": "github-pr-workflow", "description": "...", "category": "..."}, ...]

curl http://localhost:8642/v1/toolsets \
  -H "Authorization: Bearer $API_SERVER_KEY"
# → [{"name": "core", "label": "...", "description": "...", "enabled": true,
#     "configured": true, "tools": ["read_file", "write_file", ...]}, ...]
```

`/v1/skills` returns the same metadata the skills hub uses internally. `/v1/toolsets` returns toolsets resolved for the `api_server` platform with the concrete `tools` list each one expands to. Both are advertised under `endpoints.*` in `/v1/capabilities`.

## Long-term memory scoping (`X-Hermes-Session-Key`)

Multi-user frontends like Open WebUI need a stable per-channel identifier for long-term memory (Honcho, etc.) that is **independent** of the transcript-scoped `X-Hermes-Session-Id` (which rotates on `/new`). Pass `X-Hermes-Session-Key` on `/v1/chat/completions`, `/v1/responses`, or `/v1/runs` and Hermes threads it through to `AIAgent(gateway_session_key=...)`, where the Honcho memory provider uses it to derive a stable scope.

```http
POST /v1/chat/completions HTTP/1.1
Authorization: Bearer ***
X-Hermes-Session-Id: transcript-alpha
X-Hermes-Session-Key: agent:main:webui:dm:user-42
```

Rules: max 256 chars, control characters (`\r`, `\n`, `\x00`) are rejected, and the value is echoed back on responses (JSON + SSE). `/v1/capabilities` advertises support via `"session_key_header": "X-Hermes-Session-Key"`. Without the key, Honcho's `per-session` strategy produces a different scope per `session_id` — exactly the behavior Hermes had before.

## System Prompt Handling

When a frontend sends a `system` message (Chat Completions) or `instructions` field (Responses API), hermes-agent **layers it on top** of its core system prompt. Your agent keeps all its tools, memory, and skills — the frontend's system prompt adds extra instructions.

This means you can customize behavior per-frontend without losing capabilities:
- Open WebUI system prompt: "You are a Python expert. Always include type hints."
- The agent still has terminal, file tools, web search, memory, etc.

## Authentication

Bearer token auth via the `Authorization` header:

```
Authorization: Bearer ***
```

Configure the key via `API_SERVER_KEY` env var. If you need a browser to call Hermes directly, also set `API_SERVER_CORS_ORIGINS` to an explicit allowlist.

:::warning Security
The API server gives full access to hermes-agent's toolset, **including terminal commands**. `API_SERVER_KEY` is **required for every deployment**, including the default loopback bind on `127.0.0.1`. Keep `API_SERVER_CORS_ORIGINS` narrow to control browser access when you explicitly allow browser callers.
:::

## Configuration

### Environment Variables

| Variable | Default | Description |
|----------|---------|-------------|
| `API_SERVER_ENABLED` | `false` | Enable the API server |
| `API_SERVER_PORT` | `8642` | HTTP server port |
| `API_SERVER_HOST` | `127.0.0.1` | Bind address (localhost only by default) |
| `API_SERVER_KEY` | _(required)_ | Bearer token for auth |
| `API_SERVER_CORS_ORIGINS` | _(none)_ | Comma-separated allowed browser origins |
| `API_SERVER_MODEL_NAME` | _(profile name)_ | Model name on `/v1/models`. Defaults to profile name, or `hermes-agent` for default profile. |

### config.yaml

```yaml
# Not yet supported — use environment variables.
# config.yaml support coming in a future release.
```

## Security Headers

All responses include security headers:
- `X-Content-Type-Options: nosniff` — prevents MIME type sniffing
- `Referrer-Policy: no-referrer` — prevents referrer leakage

## CORS

The API server does **not** enable browser CORS by default.

For direct browser access, set an explicit allowlist:

```bash
API_SERVER_CORS_ORIGINS=http://localhost:3000,http://127.0.0.1:3000
```

When CORS is enabled:
- **Preflight responses** include `Access-Control-Max-Age: 600` (10 minute cache)
- **SSE streaming responses** include CORS headers so browser EventSource clients work correctly
- **`Idempotency-Key`** is an allowed request header — clients can send it for deduplication (responses are cached by key for 5 minutes)

Most documented frontends such as Open WebUI connect server-to-server and do not need CORS at all.

## Compatible Frontends

Any frontend that supports the OpenAI API format works. Tested/documented integrations:

| Frontend | Stars | Connection |
|----------|-------|------------|
| [Open WebUI](/user-guide/messaging/open-webui) | 126k | Full guide available |
| LobeChat | 73k | Custom provider endpoint |
| LibreChat | 34k | Custom endpoint in librechat.yaml |
| AnythingLLM | 56k | Generic OpenAI provider |
| NextChat | 87k | BASE_URL env var |
| ChatBox | 39k | API Host setting |
| Jan | 26k | Remote model config |
| HF Chat-UI | 8k | OPENAI_BASE_URL |
| big-AGI | 7k | Custom endpoint |
| OpenAI Python SDK | — | `OpenAI(base_url="http://localhost:8642/v1")` |
| curl | — | Direct HTTP requests |

## Multi-User Setup with Profiles

To give multiple users their own isolated Hermes instance (separate config, memory, skills), use [profiles](/user-guide/profiles):

```bash
# Create a profile per user
hermes profile create alice
hermes profile create bob

# Configure each profile's API server on a different port. API_SERVER_* are env
# vars (not config.yaml keys), so write them to each profile's .env:
cat >> ~/.hermes/profiles/alice/.env <<EOF
API_SERVER_ENABLED=true
API_SERVER_PORT=8643
API_SERVER_KEY=alice-secret
EOF

cat >> ~/.hermes/profiles/bob/.env <<EOF
API_SERVER_ENABLED=true
API_SERVER_PORT=8644
API_SERVER_KEY=bob-secret
EOF

# Start each profile's gateway
hermes -p alice gateway &
hermes -p bob gateway &
```

Each profile's API server automatically advertises the profile name as the model ID:

- `http://localhost:8643/v1/models` → model `alice`
- `http://localhost:8644/v1/models` → model `bob`

In Open WebUI, add each as a separate connection. The model dropdown shows `alice` and `bob` as distinct models, each backed by a fully isolated Hermes instance. See the [Open WebUI guide](/user-guide/messaging/open-webui#multi-user-setup-with-profiles) for details.

## Limitations

- **Response storage** — stored responses (for `previous_response_id`) are persisted in SQLite and survive gateway restarts. Max 100 stored responses (LRU eviction).
- **No file upload** — inline images are supported on both `/v1/chat/completions` and `/v1/responses`, but uploaded files (`file`, `input_file`, `file_id`) and non-image document inputs are not supported through the API.
- **Model field is cosmetic** — the `model` field in requests is accepted but the actual LLM model used is configured server-side in config.yaml.

## Proxy Mode

The API server also serves as the backend for **gateway proxy mode**. When another Hermes gateway instance is configured with `GATEWAY_PROXY_URL` pointing at this API server, it forwards all messages here instead of running its own agent. This enables split deployments — for example, a Docker container handling Matrix E2EE that relays to a host-side agent.

See [Matrix Proxy Mode](/user-guide/messaging/matrix#proxy-mode-e2ee-on-macos) for the full setup guide.
