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

# initialize

> Open an MCP session — negotiate the protocol version and capabilities, receive the per-chat system prompt.

The first call on every session. Returns `Mcp-Session-Id` in the response headers — include it on all subsequent calls.

## Request

```bash theme={null}
curl -sD - -X POST "http://localhost:8081/mcp" \
  -H "Authorization: Bearer $MCP_API_KEY" \
  -H "Content-Type: application/json" \
  -H "Accept: application/json, text/event-stream" \
  -H "X-Chat-Id: my-session" \
  -d '{
    "jsonrpc": "2.0",
    "id": 1,
    "method": "initialize",
    "params": {
      "protocolVersion": "2024-11-05",
      "capabilities": {},
      "clientInfo": {"name": "my-client", "version": "1.0"}
    }
  }'
```

## Response

```json theme={null}
{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "protocolVersion": "2024-11-05",
    "capabilities": {
      "tools": {},
      "resources": {}
    },
    "serverInfo": {"name": "open-computer-use", "version": "..."},
    "instructions": "<the per-chat system prompt>"
  }
}
```

Important response header: `Mcp-Session-Id: <uuid>` — store and echo on every follow-up call.

## `instructions`

`result.instructions` is the per-chat system prompt, rendered fresh from `X-Chat-Id` + `X-User-Email`. It's Tier 4 of the [six system-prompt tiers](/reference/system-prompt) and reaches clients that natively surface `InitializeResult.instructions` (Claude Desktop, MCP Inspector, OpenAI Agents SDK).

<Note>
  LiteLLM is a tool-call proxy and does not forward `instructions` to the LLM. If you're running Computer Use through LiteLLM, consume the prompt via `GET /system-prompt` instead — or via the Open WebUI filter, which does the HTTP fetch and injects the prompt into the system message for you.
</Note>

## Errors

| Status                       | Cause                                                                 |
| ---------------------------- | --------------------------------------------------------------------- |
| `401 Unauthorized`           | Missing or wrong `Authorization` when `MCP_API_KEY` is set            |
| `400 Bad Request`            | Missing `X-Chat-Id` with `SINGLE_USER_MODE=false`                     |
| `415 Unsupported Media Type` | Wrong `Accept` header — include `application/json, text/event-stream` |

## Next

* [tools/list](/api-reference/mcp/tools-list) — enumerate available tools.
* [resources/list](/api-reference/mcp/resources) — browse uploaded files.