HTTP Status Code Reference

What are HTTP Status Codes?

Every time a browser or client makes an HTTP request, the server responds with a three-digit status code that summarizes the outcome. These codes tell you whether the request succeeded, was redirected, failed because of a client mistake, or failed because of a server problem. Understanding them is essential for web development, API integration, and debugging.

This HTTP Status Code Reference lets you search by number, name, or description and browse the most common codes with clear, plain-English explanations. Each code is color-coded by its category so you can instantly tell a success from a redirect or an error.

The Five Status Code Categories

• 1xx Informational — the request was received and the process is continuing
• 2xx Success — the request was successfully received, understood, and accepted
• 3xx Redirection — further action is needed to complete the request
• 4xx Client Error — the request contains bad syntax or cannot be fulfilled
• 5xx Server Error — the server failed to fulfill a valid request

The Most Common Status Codes

200 OK means the request succeeded. 301 Moved Permanently and 302 Found handle redirects, with important SEO implications for which one you choose. 404 Not Found is the familiar broken-link error. 401 Unauthorized and 403 Forbidden relate to authentication and permissions.

On the server side, 500 Internal Server Error is the generic catch-all failure, while 502 Bad Gateway and 503 Service Unavailable point to problems with upstream servers or capacity. 429 Too Many Requests appears when you hit an API's rate limit.

Who Uses This Reference?

Front-end and back-end developers consult status codes when building and consuming APIs, deciding which code to return for a given situation, and debugging why a request behaved unexpectedly. DevOps engineers use them to interpret server logs and monitoring alerts. SEO specialists rely on them to diagnose crawl errors and redirect chains that affect search rankings.