HTTP status codes are standardized three-digit numbers returned by web servers in response to a client's request. They indicate whether the request was successful, needs redirection, contained an error, or encountered a server problem. Status codes are grouped into five classes: 1xx (informational), 2xx (success), 3xx (redirection), 4xx (client errors), and 5xx (server errors).
Key status codes for monitoring include: 200 (OK — the request succeeded), 301/302 (redirects), 403 (Forbidden — access denied), 404 (Not Found — resource doesn't exist), 500 (Internal Server Error — generic server failure), 502 (Bad Gateway — upstream server error), 503 (Service Unavailable — server overloaded or under maintenance), and 504 (Gateway Timeout — upstream server didn't respond in time).
Monitoring HTTP status codes is fundamental to uptime monitoring. A sudden increase in 5xx errors indicates server-side problems, while 4xx spikes might indicate a broken deployment or misconfigured routing. Hyperping checks the HTTP status code of every monitored endpoint and alerts when unexpected status codes are returned.
