Alert channels
Where LastSeen sends alerts, how to set each one up, and what to do when one stops working.
A channel is somewhere alerts go. Add as many as you like on Channels, with Add channel. By default every monitor's alerts go to every channel that's ready; notification profiles can route them more finely.
Ready, and why #
A channel only gets alerts once it's shown it works:
- Email: the address gets a confirmation email, and alerts start once its owner follows the link (it works for 24 hours). An address you sign in with is already confirmed.
- Everything else: choose Send test. If the test arrives, the channel is ready and shows ok.
The kinds #
| Channel | What you give it |
|---|---|
| An address. | |
| ntfy | A topic URL, like https://ntfy.sh/your-topic, on ntfy.sh or your own ntfy server. Down alerts are sent at high priority, so phones make a sound. |
| Slack | An incoming webhook URL, from a Slack app in your workspace. |
| Discord | A webhook URL, from the channel's settings (Integrations → Webhooks). |
| Telegram | Nothing: after saving, choose Connect, open the link in Telegram (it works once, for an hour), and press Start, in a chat with LastSeen's bot or in a group. |
| Webhook | A URL of yours (HTTPS, please). LastSeen POSTs JSON describing the event. |
What an alert says #
A down alert names the monitor, says why (for example, "missed 2 heartbeats (silent for 2m3s)"), and when it was last heard from. A recovery says how long it was gone. Every alert has two links:
- Snooze 1h: hold this monitor's alerts for an hour. The link opens a page with a button, so a link-checking mail filter can't snooze by accident.
- Turn off these alerts: stop alerts to this channel. For email this is also the one-click unsubscribe your mail app offers.
Links work for 30 days.
Webhooks #
Webhook requests are signed per the Standard Webhooks spec with the channel's own secret (whsec_…, shown to admins on the Channels page), so your receiver can check they're really from LastSeen. Each carries an Idempotency-Key header that stays the same when LastSeen retries, so you can drop duplicates.
When a channel fails #
If a send fails, LastSeen tries again with growing gaps, from 10 seconds up to half an hour, for about 40 minutes. An answer that says trying again won't help (a webhook that's gone, 404) is given up on at once. Either way, the channel is marked failing on the Channels page, with the reason, and later alerts are still tried. An email that bounces or is marked as spam marks its channel failing too.
A channel turned off from an alert link isn't sent anything more. To turn it back on, choose Send test (for email, confirm the address again).
Who gets which alerts #
Notification profiles (on Profiles) decide which monitors' alerts go to which channels. The default profile, Everyone, sends every monitor's alerts to every channel, and each new channel joins it. Others can pick monitors by name or tag, and add a delay before alerting, reminders while something stays down, and quiet hours in your timezone.
The daily limit #
Each organization can be sent a number of alert messages a day (200 on the Free plan). If that's reached, LastSeen sends one last message saying so, and holds further alerts until 00:00 UTC. Monitors' pages keep showing their real status meanwhile.