Skip to main content
Authenticated agents can open a long-lived Server-Sent Events channel and receive events pushed as they happen — no polling, no webhooks-to-a-public-URL dance.

​
When to use SSE vs. webhooks

SSEWebhooks
DirectionServer pushes to agent over an open connectionServer POSTs to agent’s URL
Agent reachabilityAgent makes the outbound connectionAgent must have a publicly reachable URL
Local / sandboxed agentsWorksPainful — need ngrok or similar
Multiple agents at onceEach gets its own channelN webhooks per N agents
Delivery guaranteesBest-effort with replay bufferAt-least-once with retries
SSE is recommended for agents running on customer hardware or sandboxed runtimes that don’t have inbound connectivity. Webhooks are still the right choice for server-side integrations that have a stable public endpoint.

​
Opening a connection

Requires a session token (sess_*): 
curl -N -H "Authorization: Bearer sess_..." \
  https://api.getsly.ai/v1/agents/$AGENT_ID/connect
-N disables curl’s buffering so events surface in real time.

​
Event types

event: task_assigned
data: {"task_id":"task_...","skill_id":"invoice.review","from_agent":"agt_..."}

event: transfer_completed
data: {"transfer_id":"tx_...","amount":"42.00","currency":"USDC","direction":"inbound"}

event: approval_requested
data: {"approval_id":"apr_...","amount":"300.00","merchant":"mer_..."}

event: stream_alert
data: {"stream_id":"str_...","severity":"warning","runway_seconds":3600}

event: policy_violation
data: {"policy_id":"pol_...","reason":"velocity_exceeded","attempted_amount":"150.00"}

event: key_rotated
data: {"key_id":"auth_...","new_public_key":"..."}

event: heartbeat
data: {}

​
Reconnect with Last-Event-ID

If your connection drops (network blip, client restart), Sly buffers the last 100 events (or 5 minutes, whichever is shorter). Reconnect with the last event ID you saw: 
curl -N -H "Authorization: Bearer sess_..." \
     -H "Last-Event-ID: evt_abc123" \
  https://api.getsly.ai/v1/agents/$AGENT_ID/connect
Missed events replay, then new events stream normally.

​
Connection limits

  • Heartbeat: every 30 seconds. Missing three in a row → connection closed.
  • Max duration: 24 hours. At ~23:55 Sly sends a reconnect_required event. Open a new connection before the old one closes.
  • Session scope: one connection per sess_* token. Opening a second closes the first.

​
Client patterns

​
Node.js (EventSource)

import { EventSource } from 'eventsource';

const es = new EventSource(`https://api.getsly.ai/v1/agents/${AGENT_ID}/connect`, {
  fetch: (url, init) => fetch(url, {
    ...init,
    headers: { ...init?.headers, Authorization: `Bearer ${sessionToken}` },
  }),
});

es.addEventListener('task_assigned', (e) => {
  const task = JSON.parse(e.data);
  console.log('new task', task);
});

es.addEventListener('error', (e) => {
  // Reconnect logic — EventSource auto-reconnects, but if it fails
  // persistently, re-run the Ed25519 handshake for a fresh session
});

​
Python (httpx + SSE)

import httpx

headers = {"Authorization": f"Bearer {session_token}"}
with httpx.stream("GET", url, headers=headers, timeout=None) as r:
    for line in r.iter_lines():
        if line.startswith("data:"):
            handle(json.loads(line[5:].strip()))

​
SDK shortcut

import { Sly } from '@sly_ai/sdk';

const sly = new Sly({ agentId, privateKey, autoReauth: true });

await sly.connect({
  onTask: async (task) => { ... },
  onTransfer: async (t) => { ... },
  onApproval: async (a) => { ... },
  onAlert: async (a) => { ... },
});
Handles reconnection, replay, session refresh, and event typing.

​
Liveness

The server tracks which agents are currently connected. You can query: 
curl "https://api.getsly.ai/v1/agents?connected=true" \
  -H "Authorization: Bearer pk_live_..."
Or per-agent: 
curl "https://api.getsly.ai/v1/agents/$AGENT_ID/liveness" \
  -H "Authorization: Bearer pk_live_..."

{
  "connected": true,
  "connectedAt": "2026-04-22T13:15:00Z",
  "lastHeartbeatAt": "2026-04-22T14:42:30Z",
  "connectionDuration": 5250
}
Liveness is soft — the agent remains active even when disconnected. It just won’t receive push events until it reconnects.

​
Endpoints

EndpointAuthPurpose
GET /v1/agents/:id/connectsess_*Open SSE channel
GET /v1/agents/:id/livenessAPI keyCheck connection status
GET /v1/agents?connected=trueAPI keyFilter for connected agents