Source: https://uptimeify.io/resources/platform-and-support/glossary/http-status-code

# HTTP Status Code

> An HTTP status code is a three-digit number a server returns to indicate the outcome of a request, such as 200 (OK), 404 (Not Found), or 500 (Server Error).

Status codes group into families: 2xx success, 3xx redirects, 4xx client errors, and 5xx server errors. Monitoring watches for unexpected codes, a 500 where a 200 belongs, or a redirect that breaks, which often signal an outage even when the server still answers.

Checking the status code (not just whether a connection opened) is what separates real uptime monitoring from a simple ping.