> ## Documentation Index
> Fetch the complete documentation index at: https://docs.usefused.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Neutral API

> Use portable sessions, responses, SSE events, WebSockets, and the playground.

The neutral API keeps product-facing behavior stable across frameworks and authoring modes.

## Endpoints

| Endpoint                                          | Purpose                               |
| ------------------------------------------------- | ------------------------------------- |
| `GET /agent`                                      | Agent identity and routes             |
| `POST /sessions`                                  | Create a session                      |
| `GET /sessions`                                   | List sessions                         |
| `GET/PATCH/DELETE /sessions/{id}`                 | Read, update, or delete a session     |
| `GET /sessions/{id}/messages`                     | Read the transcript                   |
| `POST /sessions/{id}/assets`                      | Upload a session-owned media asset    |
| `HEAD/GET/DELETE /sessions/{id}/assets/{assetId}` | Inspect, download, or delete an asset |
| `POST /responses`                                 | Run JSON or SSE responses             |
| `WS /live`                                        | Run a live WebSocket session          |
| `GET /healthz`                                    | Check process health                  |
| `GET /.well-known/agent-card.json`                | Discover the Agent Card               |

## Response modes

<Tabs>
  <Tab title="JSON">
    Send one request to `POST /responses` and receive one completed response.
  </Tab>

  <Tab title="SSE">
    Set `"stream": true`. The stream starts with `response.created` and ends with `response.completed` or `error`.
  </Tab>

  <Tab title="WebSocket">
    Connect to `/live`, send a `connect` frame, wait for `session.connected`, then send `response.create` frames.
  </Tab>
</Tabs>

All modes use the same portable event names. Native metadata stays under `adk` or `langgraph`.

Typed input, output, and media use the same contract in every mode. See [Accept multimodal data](/harnest/build/models-and-libraries/typed-multimodal-contracts).

## Pagination properties

| Property       | Value                                             |
| -------------- | ------------------------------------------------- |
| Default limit  | 100                                               |
| Accepted limit | `1..100`                                          |
| Next page      | Return `nextCursor` unchanged                     |
| Final page     | `nextCursor` is `null`                            |
| Cursor scope   | User; transcript cursors also bind to the session |

Malformed or cross-user cursors return `400`.

## Playground

The playground uses only the neutral API. It supports sessions, state, tool activity, JSON, SSE, and WebSocket conversations.

| Auth path                 | Browser behavior              |
| ------------------------- | ----------------------------- |
| HTTP and SSE bearer token | Kept in page memory           |
| Authenticated WebSocket   | Requires a same-origin cookie |

Browsers cannot add arbitrary authorization headers to a WebSocket handshake.