API Server

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.

Quick Start

1. Enable the API server

Add to ~/.hermes/.env:

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

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:

# 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 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:

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

Response:

{
  "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:

{
  "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:

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

Response:

{
  "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:

{
  "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:

{
  "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:

{"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 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.

{
  "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.

{
  "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.

{
  "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.

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.

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. When binding to a non-loopback address like 0.0.0.0, API_SERVER_KEY is required. Also keep API_SERVER_CORS_ORIGINS narrow to control browser access.

The default bind address (127.0.0.1) is for local-only use. Browser access is disabled by default; enable it only for explicit trusted origins. :::

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	(none)	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

# 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:

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	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:

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

# Configure each profile's API server on a different port
hermes -p alice config set API_SERVER_ENABLED true
hermes -p alice config set API_SERVER_PORT 8643
hermes -p alice config set API_SERVER_KEY alice-secret

hermes -p bob config set API_SERVER_ENABLED true
hermes -p bob config set API_SERVER_PORT 8644
hermes -p bob config set API_SERVER_KEY bob-secret

# 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 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 for the full setup guide.