About HTTP Status Code Reference

This tool provides an instant, filterable reference for every standard HTTP status code across all five classes: 1xx Informational, 2xx Success, 3xx Redirection, 4xx Client Error, and 5xx Server Error. Each entry includes the official status name and a concise explanation of what triggers that response.

Bookmark this page as a quick lookup while debugging API responses, reading server logs, or writing backend handlers. No login or installation is required — every code and description loads instantly in your browser.

Common Use Cases

Debugging unexpected API responses by quickly identifying what a 409 Conflict or 422 Unprocessable Entity means
Writing backend middleware and needing to confirm the correct code for a redirect (301 vs 302 vs 307)
Reading server error logs and distinguishing between 503 Service Unavailable and 504 Gateway Timeout
Teaching HTTP fundamentals to junior developers or reviewing codes during code review sessions

How to Use

Use the filter buttons at the top to show only a specific class (e.g., 4xx Client Errors)
Use the search box to jump directly to a code number or keyword like "redirect" or "unauthorized"
Click any status card to expand its full description and usage notes
Use the "All" filter to reset and browse every code across all classes

Frequently Asked Questions

What is the difference between 301 and 302 redirects?

A 301 Moved Permanently tells clients and search engines that the resource has moved to a new URL forever — search engines transfer SEO ranking to the new URL. A 302 Found is a temporary redirect; search engines keep indexing the original URL and the ranking stays with it.

When should an API return 400 vs 422?

400 Bad Request means the server could not parse the request at all — for example, malformed JSON syntax. 422 Unprocessable Entity means the request was well-formed but semantically invalid, such as a missing required field or a value that fails business-logic validation.

What causes a 503 vs a 504 error?

503 Service Unavailable means the server itself is temporarily unable to handle requests — often due to overload or maintenance. 504 Gateway Timeout means an upstream server (behind a proxy or load balancer) did not respond in time; the server in the middle received nothing back from the dependency it was waiting on.