My monitor reports downtime but the site is clearly up — what's going on?

My monitor reports downtime but the site is clearly up — what's going on?

Q: I get downtime alerts but when I check, the site loads fine for me. Is my monitor broken?

A: Often the monitor is fine and your own infrastructure is blocking it. A reader chased phantom outages for weeks — 22 false 'down' alerts in a month, all recovering within a minute. The cause: their WAF rate-limited the monitoring probe's IP because frequent identical requests looked like a bot attack. The site was up for humans, blocked for the probe.

They allowlisted the monitoring provider's published IP ranges and added a custom user-agent header the WAF recognized. False positives dropped from 22 to zero the next month.

The follow-up: before assuming the monitor lies, check what your probe actually received. A 403 or 429 in the check's response body tells you instantly it's a blocking issue, not real downtime. The fix is almost always allowlisting the prober, not loosening the interval.

Got a question? Drop it in the comments.