Glossary · Monitoring

False Negative (Monitoring)

In monitoring, a false negative is a missed failure: the check reports healthy while real users are affected, so no alert is sent.

Updated October 6, 2026

A false negative in monitoring happens when something is broken but the monitor reports success. The outage goes undetected until a customer complains.

Why it matters

False negatives are more dangerous than false positives because the failure is silent. Usually the check is too shallow. It confirms that a server answers but not that the application works. A homepage served from a CDN cache can return HTTP 200 while the login, database or checkout behind it is broken.

Example

A shop's monitor requests / and gets 200 from a cached copy. Meanwhile the checkout API returns errors for every order. Adding a keyword check and an API check closes the gap:

check 1: GET /            expect status 200, body contains "Add to cart"
check 2: GET /api/health  expect status 200, body contains "db":"ok"
check 3: POST /api/cart   expect status 201

Common mistakes

  • Relying on status code alone. Some failures return 200 with an error page.
  • Monitoring only the front page and not critical journeys.
  • Checking from one region, so regional failures are missed.
  • Long check intervals that skip short outages.

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