An HTTP status code is a three-digit number included in every HTTP response that indicates the outcome of the request. Status codes are grouped into five classes: 1xx (informational), 2xx (success), 3xx (redirection), 4xx (client error), and 5xx (server error). Each code conveys specific information about what happened when the server processed the request.
For URL shortening services, the 3xx class is most relevant. The 301 (Moved Permanently) and 302 (Found) codes are the workhorses of URL redirection. The 200 (OK) code indicates successful content delivery, while 404 (Not Found) signals that a short code does not exist in the database. Understanding these codes is essential for debugging redirect issues and monitoring service health. HTTP protocol books on Amazon provide comprehensive references.
Beyond the common codes, several less-known status codes are relevant to URL shortening. The 410 (Gone) code indicates that a resource has been intentionally removed, which is useful for expired short URLs. The 429 (Too Many Requests) code is used for rate limiting API access. The 503 (Service Unavailable) code signals temporary downtime.
Monitoring HTTP status codes is a key operational practice. Tracking the distribution of response codes over time reveals patterns such as increasing 404 rates (indicating broken links), spikes in 5xx errors (indicating server issues), or unusual redirect patterns. DevOps monitoring books on Amazon cover monitoring strategies.