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Monitors and check types

12 check types, what each verifies, and the knobs that matter: assertions, inline subchecks, dual-stack behavior, intervals.

The 12 types

http, http_headers, tcp, dns, dns_hygiene, domain, ssl_cert, smtp, imap, ping, traceroute, and agent. The check-type reference explains each in plain language; this page covers the configuration details.

HTTP monitors

  • Assertions: expected status code, a keyword the body must contain, or a regular expression against the body.
  • Inline subchecks: an http monitor carries TLS-certificate (expiry, issuer, self-signed detection), security-header, and DNS-hygiene subchecks, so one monitor covers what used to take four.
  • Redirects: followed up to 5 hops; every hop is validated against SSRF targets (private ranges, link-local, metadata endpoints) before it is fetched.

Dual-stack behavior

Checks run across all A and AAAA records with per-family and per-IP results. Whether an IPv6-only failure counts as degraded or as failed is your call, per monitor. dns_ms is reported apart from total latency.

DNS specifics

A dns monitor compares the answer set against your expectation, and can cross-reference its answers against another monitor’s answer set; a divergence runs through the normal incident pipeline. dns_hygiene checks SPF, DMARC, and CAA as configuration. domain watches NS, SOA, DNSSEC, and WHOIS expiry.

Intervals

Intervals are configured per monitor; the floor depends on the plan: Free 300 s, Pulse 60 s, Sentinel 30 s, Command 15 s, Enterprise 10 s. Full limit tables live on plans and limits.

Agent monitors

The agent type binds a monitor to a host agent: availability with a grace period, CPU, memory, and disk against thresholds, and named services with anti-flapping grace. Missing data counts as pending, never as a false alarm; a silent agent counts as down.