Know before your customers do

Checking something once tells you about today. This keeps watching and emails you the moment it changes: your sending IPs against the blacklists, your certificates before they expire, your domains — including the transfer lock that stops someone moving them — and the DNS records themselves, so you find out the day your MX or your nameservers move. Add a webhook if you would rather it land in Slack.

Checks run from one machine, once per interval. For a blacklist entry or an expiry date that is plenty: both change slowly. For uptime it would not be, so the availability check asks two reference sites whenever the target fails — if those fail too, the one with the problem is this server, and that round is not counted against you and raises no alert. It reports the second confirmed failure, never the first. Domain data comes from the registry itself — over RDAP, or over WHOIS where the registry has no RDAP — so it is only available for the TLDs whose registry publishes the expiry date: .es and .de, among others, do not.

This server cannot send email yet. Changes are still recorded and shown here, and a webhook works — but no alert will reach your inbox.