HTTP Status Code Lookup

What are HTTP status codes?

HTTP status codes are three-digit numbers a server returns with every response to tell the client what happened. They're grouped into five classes: 1xx (informational), 2xx (success), 3xx (redirects), 4xx (client errors), and 5xx (server errors). Understanding status codes is essential for debugging APIs, CDNs, reverse proxies, and browser network errors.

HTTP status code lookup

Enter a status code to get a quick explanation, common causes, and typical fixes. No network calls — works offline.

Status code classes explained

• 1xx — Informational: the request was received and processing is continuing (e.g. 101 Switching Protocols for WebSockets)
• 2xx — Success: the request was received, understood, and accepted (200 OK, 201 Created, 204 No Content)
• 3xx — Redirection: the client must take additional action to complete the request (301 Moved Permanently, 302 Found, 304 Not Modified)
• 4xx — Client errors: the request contains bad syntax or cannot be fulfilled (400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 429 Too Many Requests)
• 5xx — Server errors: the server failed to fulfill a valid request (500 Internal Server Error, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout)

Common codes to look up

• 301 — permanent redirect (update links; tells Google the old URL has moved)
• 404 — page not found (check the URL and routing rules)
• 429 — rate limited (back off and retry with exponential delay)
• 500 — server error (check server logs and recent deploys)
• 502 / 504 — upstream or proxy issues (check the origin server health)

SEO and status codes

• Use 301 (not 302) for permanent redirects so link equity passes to the new URL
• 404 pages should return a real 404 status, not 200 (avoid "soft 404s")
• 410 Gone explicitly tells crawlers a page was removed permanently
• 503 with a Retry-After header tells crawlers the site is temporarily down