What does an HTTP check verify?
Each check requests your URL from outside your infrastructure and verifies the response: the expected status code, optional body-contains / CSS-selector / XPath assertions, and the response time. A failed assertion or a request error counts as a failed check.
How does PageLantern identify itself to my server?
Every probe sends a User-Agent header of the form "Mozilla/5.0 (compatible; PageLantern-Probe/1.0; +https://pagelantern.com/docs/website-monitoring)", so you can identify (or allowlist) monitoring traffic in your logs, WAF, and rate limits. Match on the substring "PageLantern-Probe" rather than the whole string — the surrounding token order and contact URL can change, and an exact-match allowlist rule would silently stop matching.
What happens when a check fails?
Consecutive failures cross your alert threshold (default 2), an incident opens automatically, and alerts go to your configured channels. When checks succeed again, recovery is detected and the incident resolves — with a recovery notice to the same channels.