What are HTTP Status Codes?
HTTP status codes are standardized three-digit response codes returned by servers as part of the HTTP protocol. They are grouped into five classes: 1xx (informational), 2xx (success), 3xx (redirection), 4xx (client error), and 5xx (server error). Each code communicates a specific outcome — 200 OK means the request succeeded, 404 Not Found means the resource does not exist, and 500 Internal Server Error indicates a server-side failure. These codes are defined in RFC 7231 and related RFCs.
Why HTTP Status Codes Matter
Correct use of status codes is fundamental to building reliable APIs and web applications. They tell clients how to handle responses: follow a redirect (301/302), retry later (429/503), or show an error message (400/404/500). Search engines use codes like 301 for permanent redirects and 404 for broken links in their crawling. Monitoring systems watch for 5xx codes to detect outages. Using the wrong code can break caching, confuse clients, and hurt SEO rankings.
Common Status Codes Every Developer Should Know
The most frequently encountered codes are: 200 (OK), 201 (Created), 204 (No Content), 301 (Moved Permanently), 302 (Found/Temporary Redirect), 304 (Not Modified), 400 (Bad Request), 401 (Unauthorized), 403 (Forbidden), 404 (Not Found), 405 (Method Not Allowed), 429 (Too Many Requests), 500 (Internal Server Error), 502 (Bad Gateway), and 503 (Service Unavailable). Knowing when to return each code is essential for building professional-quality APIs.
Best Practices for Using Status Codes
Always return the most specific code that applies. Use 201 after creating a resource, not just 200. Return 204 for successful DELETE operations with no body. Use 400 for validation errors and include a descriptive error body. Return 429 with a Retry-After header for rate-limited requests. Avoid using 200 for error responses — that breaks client-side error handling. Log 5xx errors for monitoring and alerting.
