What is the difference between 301 and 302?

301 is a permanent redirect: search engines transfer ranking to the new URL and update their index. 302 is temporary and the original URL is kept. If a POST must stay a POST after redirecting, use 308 and 307 respectively.

What is the difference between 401 and 403?

401 means you are not authenticated or authentication failed; logging in or sending a valid token fixes it. 403 means the server knows who you are but you lack permission, so logging in again will not help.

What causes 502 vs 504?

Both come from a gateway or reverse proxy such as Nginx or a CDN. 502 Bad Gateway means the upstream returned an invalid response, often because the backend crashed or the port is wrong; 504 Gateway Timeout means the upstream took longer than the proxy was willing to wait.

Do I need to sign up or pay?

No. The site is completely free, needs no account and has no usage limits.

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🚦HTTP Status Codes List - Meaning of 200, 301, 404, 502 & More

When debugging an API, reading Nginx logs or troubleshooting a website, the status code is usually the first clue. This reference covers every standard HTTP status code defined by RFC 9110 and related specs (1xx informational, 2xx success, 3xx redirection, 4xx client errors, 5xx server errors), each with a plain-language explanation of when it appears and what usually causes it, including the differences between 301, 302, 307 and 308, between 401 and 403, and between 502 and 504. Type a code, name or keyword (like "cache" or "timeout") to filter; common codes are highlighted.

Free · No sign-up · Runs in your browserLast updated: 2026-10-26

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How to use HTTP Status Codes

1Type a status code (e.g. 404 or 5), name or keyword in the search box
2Or filter by class with the 1xx–5xx buttons
3Read the name and detailed explanation of each code

FAQ

What is the difference between 301 and 302?: 301 is a permanent redirect: search engines transfer ranking to the new URL and update their index. 302 is temporary and the original URL is kept. If a POST must stay a POST after redirecting, use 308 and 307 respectively.
What is the difference between 401 and 403?: 401 means you are not authenticated or authentication failed; logging in or sending a valid token fixes it. 403 means the server knows who you are but you lack permission, so logging in again will not help.
What causes 502 vs 504?: Both come from a gateway or reverse proxy such as Nginx or a CDN. 502 Bad Gateway means the upstream returned an invalid response, often because the backend crashed or the port is wrong; 504 Gateway Timeout means the upstream took longer than the proxy was willing to wait.
Do I need to sign up or pay?: No. The site is completely free, needs no account and has no usage limits.