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

# Server: A2U

> Deploy agents with A2U (Agent-to-User) event streaming

Deploy agents with A2U (Agent-to-User) event streaming for real-time agent-to-user communication.

## CLI

```bash theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
pip install "praisonai[serve]"
export OPENAI_API_KEY="your-key"

# Start A2U server
praisonai serve a2u --port 8083
```

**Expected Output:**

```
🚀 Starting A2U Event Stream Server...
   Host: 127.0.0.1
   Port: 8083
📡 Event stream: http://127.0.0.1:8083/a2u/events/events
ℹ️  Info: http://127.0.0.1:8083/a2u/info
✅ Server started at http://127.0.0.1:8083
```

## Python

```python theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
from fastapi import FastAPI
import uvicorn
from praisonai.endpoints.a2u_server import (
    create_a2u_routes,
    emit_agent_started,
    emit_agent_response,
    emit_agent_completed,
)

app = FastAPI(title="PraisonAI A2U Server")

# Add A2U routes
create_a2u_routes(app)

# Add discovery endpoint
@app.get("/__praisonai__/discovery")
async def discovery():
    return {
        "schema_version": "1.0.0",
        "server_name": "praisonai-a2u",
        "providers": [{"type": "a2u", "name": "A2U Event Stream"}],
        "endpoints": [{"name": "events", "provider_type": "a2u"}]
    }

uvicorn.run(app, host="0.0.0.0", port=8083)
```

**Expected Output:**

```
INFO:     Started server process
INFO:     Waiting for application startup.
INFO:     Application startup complete.
INFO:     Uvicorn running on http://0.0.0.0:8083
```

## A2U Endpoints

| Endpoint               | Method | Description                  |
| ---------------------- | ------ | ---------------------------- |
| `/a2u/info`            | GET    | Server info and capabilities |
| `/a2u/events/<stream>` | GET    | SSE event stream             |
| `/a2u/subscribe`       | POST   | Subscribe to events          |
| `/a2u/unsubscribe`     | POST   | Unsubscribe from events      |

## Event Types

| Event Type        | Description                  |
| ----------------- | ---------------------------- |
| `agent.started`   | Agent started processing     |
| `agent.thinking`  | Agent is thinking/processing |
| `agent.response`  | Agent generated response     |
| `agent.completed` | Agent completed task         |
| `agent.error`     | Agent encountered error      |
| `tool.called`     | Tool was invoked             |
| `tool.result`     | Tool returned result         |

## Subscribe to Events

```bash theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
# Get server info
curl http://localhost:8083/a2u/info

# Subscribe to events
curl -X POST http://localhost:8083/a2u/subscribe \
  -H "Content-Type: application/json" \
  -d '{"stream": "events", "filters": ["agent.response"]}'

# Stream events (SSE)
curl -N http://localhost:8083/a2u/events/events
```

**Subscribe Response:**

```json theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
{
  "subscription_id": "sub_abc123",
  "stream": "events",
  "stream_url": "/a2u/events/events"
}
```

## Emit Events from Agent

```python theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
from praisonai.endpoints.a2u_server import (
    emit_agent_started,
    emit_agent_thinking,
    emit_agent_response,
    emit_agent_completed,
)

# In your agent code
agent_id = "agent-123"

emit_agent_started(agent_id, "MyAgent")
emit_agent_thinking(agent_id, "Processing your request...")
emit_agent_response(agent_id, "Here is my response")
emit_agent_completed(agent_id, {"status": "success"})
```

## SSE Event Format

```
event: agent.started
data: {"agent_id": "agent-123", "agent_name": "MyAgent"}
id: evt_abc123

event: agent.response
data: {"agent_id": "agent-123", "content": "Hello!"}
id: evt_def456
```

## Python Client

```python theme={"theme":{"light":"vitesse-light","dark":"vitesse-dark"}}
import requests
import sseclient

# Subscribe to events
url = "http://localhost:8083/a2u/events/events"
response = requests.get(url, stream=True)
client = sseclient.SSEClient(response)

for event in client.events():
    print(f"Event: {event.event}")
    print(f"Data: {event.data}")
```

## CLI Options

| Option      | Default   | Description                |
| ----------- | --------- | -------------------------- |
| `--port`    | 8083      | Server port                |
| `--host`    | 127.0.0.1 | Server host                |
| `--api-key` | -         | API key for authentication |

## Troubleshooting

| Issue              | Fix                                  |
| ------------------ | ------------------------------------ |
| Port in use        | `lsof -i :8083`                      |
| Missing deps       | `pip install "praisonai[serve]"`     |
| No events          | Check agent is emitting events       |
| SSE not connecting | Check firewall, use `host="0.0.0.0"` |

## Related

* [A2A Server](./a2a) - Agent-to-agent protocol
* [Agents Server](./agents) - Deploy as HTTP server
* [Endpoints CLI](/docs/cli/endpoints) - Client for all server types