External monitoring
Checks run FROM MonitorFree's side, against your server/site — independent of whether the agent is even installed.
Monitor types
| Type | What it does |
|---|---|
| HTTP | Requests a URL on an interval you set, checks the response status code is in the expected range (default 200–299), and optionally asserts a keyword is (or isn't) present in the response body. |
| TCP port | Attempts a raw TCP connection to host:port — for anything that isn't HTTP (a database, a custom protocol, SSH itself on another box). |
| Heartbeat | The inverse of the other two: MonitorFree gives you a unique URL, and you ping it (from a cron job, a CI pipeline, a backup script). If no ping arrives within the interval plus a grace period, it's marked down — for monitoring things that run periodically rather than continuously. |
| Blacklist | Checks your domain/IP against a curated set of DNS-based blacklists (Spamhaus ZEN, SpamCop, Barracuda, and others) — catches your mail server or IP getting blacklisted before your emails start bouncing. |
SSL & domain expiry
On an HTTPS monitor, SSL expiry checking is on by default — MonitorFree inspects the live certificate and warns before it expires. Domain expiry is opt-in (a WHOIS lookup, which is slower and rate-limited by registries, so it's not run unconditionally on every check). Turning on domain expiry also enables nameserver tracking — MonitorFree remembers your domain's last-known nameservers and can flag an unexpected change.
Expiry warnings are throttled to at most once a week per certificate/domain (not re-sent every check cycle) so you get one heads-up, not a daily nag as the deadline approaches.
Status semantics
A single failed check doesn't immediately mark a monitor "down" — consecutive_failures
debounces a transient blip the same way alert-rule durations do. Heartbeat monitors work the opposite
way: "down" means an absence of a signal within the expected window, not a failed request.
monitor_down alert-rule metric described in
Monitoring & alerts — set up delivery there.