Uptime and certificate alerts in Slack

hostnag posts every alert, uptime, certificate and more, to a Slack channel, with an Acknowledge button when the alert allows it.

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Included on Pro and Business.

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Down

Header: [Critical] https://www.example.com/ is down
Text: Down from 2 of 3 locations (US East, Frankfurt). Last error: unexpected_status: 503.
Group: Client A
Monitor: Marketing site
Target: https://www.example.com/
Down since: 12 Sept 2026, 07:58 UTC
Locations: US East, Frankfurt
Status code: 503
Last error: unexpected_status: 503
Buttons: Acknowledge, Open monitor

Set up

01
Create an incoming webhook
In Slack, add an Incoming Webhook to the channel and copy the URL it gives you.
02
Paste the webhook URL
The URL must start with https://hooks.slack.com; hostnag stores it as a secret, never in plain config.

What arrives

Rendered by the same code that sends it.

Back up

Header: [Recovered] https://www.example.com/ is back up after 1 h 15 min
Text: https://www.example.com/ answered again from every location. It was down for 1 h 15 min.
Group: Client A
Monitor: Marketing site
Target: https://www.example.com/
Down since: 12 Sept 2026, 07:58 UTC
Duration: 1 h 15 min
Buttons: Acknowledge, Open monitor

Heartbeat missed

Header: [Critical] Nightly backup missed its heartbeat
Text: nightly-backup has not pinged in time: 25 min overdue. The job may have stopped, hung or lost its way out.
Group: Client A
Monitor: Nightly backup
Pings as: nightly-backup
Missing since: 12 Sept 2026, 07:58 UTC
Last error: no_ping: 25 min overdue
Buttons: Acknowledge, Open monitor

Routing

Every alert follows the group's alert policy: which channels a route goes to and the minimum severity each one takes, in bands of critical, warning and info. Quiet hours hold non-critical alerts for email, Slack, Discord, SMS, Teams and Telegram until the window closes, then deliver one digest; critical alerts are never held, and webhook, PagerDuty and Opsgenie always deliver right away since they hand off to another machine, not a person. A maintenance window on a group or a monitor suppresses alerts for its duration while checks keep running. An alert nobody acknowledges escalates through up to three tiers, each after its own number of minutes, and can be acknowledged with one tap from the alert message itself.

Questions

Can I acknowledge an alert from Slack?

Yes. Every alert that can be acknowledged carries an Acknowledge button that opens the signed link.

What happens during quiet hours?

Non-critical alerts wait and arrive as one digest when the window closes; critical alerts are never held.

Watches

Alerting and status pagesEvery alert routed to the right channel at the right severity, held during quiet hours and maintenance, escalated until it's acknowledged.Uptime monitoringWebsites, APIs and anything that answers on a port, checked every minute from up to four places, with a failure confirmed before anyone is paged.Heartbeat monitoringA minted URL for anything that runs on its own schedule: a job that goes quiet becomes an alert, not a surprise weeks later.

Add a host. Hear about it in Slack.

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