Alert Channels

Email

Email alerts are included on every plan, including the free tier. Alert emails include: the monitor name, URL, failure reason, timestamp, and a link to the monitor dashboard.

Setup

1. Go to Alert Channels → Add Channel
2. Select Email
3. Enter the email address (can be a team distribution list)
4. Click Send Test to verify delivery
5. Link the channel to one or more monitors

Slack

is0k posts rich Slack messages using Block Kit formatting — color-coded by status (green = up, red = down), with response time, error details, and a button to open the monitor.

Setup

1. In Slack: Apps → Incoming Webhooks → Add to Slack
2. Choose the channel to post to, then click Allow
3. Copy the Webhook URL (starts with https://hooks.slack.com/services/...)
4. In is0k: Alert Channels → Add Channel → Slack → paste the webhook URL
5. Click Send Test — you should see a test message in your Slack channel

Discord

is0k sends Discord embeds with color-coded status (green/red/yellow), monitor details, and response time.

Setup

1. In Discord: right-click your server → Server Settings → Integrations → Webhooks
2. Click New Webhook, choose the channel, copy the webhook URL
3. In is0k: Alert Channels → Add Channel → Discord → paste the URL
4. Click Send Test

Telegram

Receive beautifully formatted Telegram messages with emoji status indicators and monitor details.

Setup

1. Open Telegram, search for @BotFather
2. Send /newbot and follow the prompts to create a bot
3. Copy the Bot Token (looks like 123456789:ABCdef...)
4. Start a conversation with your bot, or add it to a group/channel
5. Get your Chat ID by forwarding a message to @userinfobot
6. In is0k: Alert Channels → Add Channel → Telegram → enter bot token + chat ID

Webhooks

Send alert payloads to any HTTP endpoint. is0k signs every request with HMAC-SHA256 so you can verify authenticity. Failed deliveries are retried with exponential backoff (1s, 2s, 4s).

Payload format

POST https://your-server.com/webhook
Content-Type: application/json
X-Is0k-Signature: sha256=<hmac>

{
  "event": "monitor.down",
  "monitor": {
    "id": "mon_abc123",
    "name": "Production API",
    "url": "https://api.example.com/health",
    "type": "http"
  },
  "check": {
    "status": "down",
    "status_code": 503,
    "response_time_ms": 12043,
    "error": "connection timeout",
    "region": "us-east",
    "checked_at": "2026-02-20T14:32:11Z"
  }
}

Verifying the signature

// Node.js example
import crypto from 'crypto';

const signature = req.headers['x-is0k-signature'];
const expectedSig = 'sha256=' + crypto
  .createHmac('sha256', process.env.WEBHOOK_SECRET)
  .update(req.body)
  .digest('hex');

if (!crypto.timingSafeEqual(
  Buffer.from(signature),
  Buffer.from(expectedSig)
)) {
  return res.status(401).send('Invalid signature');
}

Event types

Alert Thresholds & Rate Limiting

Avoid alert fatigue with configurable thresholds:

• Failure threshold — Number of consecutive failures before alerting (default: 2). Prevents false positives from transient issues.
• Rate limiting — Alerts are de-duplicated within a 5-minute window per monitor/channel. You won't receive 50 alerts if a check fails repeatedly.
• Recovery alerts — Automatically sent when a monitor recovers, with total downtime duration.