HTTP Status Codes

HTTP status codes are three-digit numbers returned by a server in response to every HTTP request. They tell the client (browser, API consumer, crawler) whether the request succeeded, failed, or needs further action. Understanding these codes is essential for debugging APIs, fixing broken pages, and building robust web applications.

Codes are grouped by their first digit: 1xx (informational — request received, processing), 2xx (success — request accepted and processed), 3xx (redirection — further action needed), 4xx (client error — bad request from the caller), and 5xx (server error — the server failed to fulfill a valid request).

The most commonly encountered codes are 200 OK (success), 301/302 (redirects), 404 Not Found (page doesn't exist), 401/403 (authentication/authorization failures), and 500 Internal Server Error (something broke on the server). This reference covers all standard codes with explanations and common causes.