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Core Concepts

Server Error Detection

Server Error Detection

A page can return 200 OK while printing PHP deprecation warnings above the header, a WordPress critical-error page, or an SQL error where content should be. Status-code monitoring passes all of these. Server error detection reads the page body and recognizes the shape of leaked server errors, with nothing to configure.

What It Detects

  • PHP errors - Warnings, notices, deprecations, and fatal errors with their file path and line number
  • PHP stack traces - Raw exception traces rendered as page text
  • WordPress failure pages - "There has been a critical error on this website" and "Error establishing a database connection"
  • SQL errors - SQLSTATE codes, MySQL syntax errors, and access-denied messages
  • Python tracebacks - "Traceback (most recent call last)" output
  • Framework debug pages - Laravel, Symfony, and Yii/Craft CMS exception pages leaking in production
  • ASP.NET error pages - "Server Error in '/' Application"

How It Works

  1. Sentinel fetches the monitored page (at most once every 5 minutes per monitor)
  2. The body is matched against a library of structural error signatures
  3. A match opens a warning-severity incident recording exactly what was found
  4. Notifications go to your configured channels
  5. The incident resolves automatically once the page comes back clean

Enabling It

  • New monitors: on by default, nothing to do
  • Existing monitors: off by default, so the feature's launch never opens incidents for warnings a site has quietly carried. Enable it under the monitor's advanced settings: "Alert when server error text is visible on the page"

Why It Doesn't False-Positive

Every signature requires the structure of a real leak, not just error vocabulary. "Deprecated:" alone matches nothing; Deprecated: ... in /path/file.php on line 525, the exact shape PHP emits, is what matches. A blog post about fixing PHP warnings will not trigger an alert.

Severity

Detections open a warning-severity incident, not an outage. The site is up; it is leaking. Keep in mind that visible error output exposes server paths, and a framework debug page in production can expose environment details, so it is worth fixing promptly even though nothing is down.

Server error detection is included on every plan. For custom content rules beyond the built-in signatures, see keyword monitoring.

Keyword MonitoringAPI Monitoring