HTTP Status Codes Reference

Quick reference for all HTTP status codes with SEO implications. For implementation details see HTTP Status Codes and Redirects.

1xx — Informational (rarely seen)

Code	Name	Notes
100	Continue	Sent before final response. Crawlers don’t care.
101	Switching Protocols	Used for HTTP/2 upgrade, WebSocket. Crawlers don’t care.

Code	Name	SEO meaning
200	OK	Normal indexable response.
201	Created	After POST form submission. Not for content URLs.
202	Accepted	Async processing started. Not for content URLs.
204	No Content	API responses. Not for content URLs.
206	Partial Content	Range requests (resuming downloads). Crawlers handle automatically.

Code	Name	SEO meaning
300	Multiple Choices	Rarely used. Server presents options.
301	Moved Permanently	Link equity transfers. Preferred for permanent moves.
302	Found	Temporary. Link equity stays at OLD URL. Use sparingly.
303	See Other	After POST, redirect to GET. Used in form submission flows.
304	Not Modified	Conditional GET. Crawler used `If-Modified-Since` and content hasn’t changed. Saves bandwidth.
307	Temporary Redirect	Like 302 but HTTP method preserved (POST stays POST).
308	Permanent Redirect	Like 301 but HTTP method preserved.

Code	Name	SEO meaning
400	Bad Request	Malformed request. Crawlers may retry.
401	Unauthorized	Authentication required. Crawlers treat as inaccessible.
403	Forbidden	Access denied. Crawlers don’t index.
404	Not Found	URL doesn’t exist. Eventually de-indexed.
405	Method Not Allowed	Wrong HTTP method (e.g., POST to GET-only endpoint).
406	Not Acceptable	Content negotiation failed (Accept-Language mismatch, etc.).
408	Request Timeout	Client took too long. Crawlers will retry.
409	Conflict	Resource state conflict (rare in HTTP responses to crawlers).
410	Gone	Intentional deletion. Faster de-indexing than 404.
411	Length Required	Missing Content-Length header. Server-config issue.
412	Precondition Failed	If-Match header didn’t match. Rare for crawlers.
413	Payload Too Large	Request body too big. Not for crawlers normally.
414	URI Too Long	URL exceeds server limit. Probably an attack or bug.
415	Unsupported Media Type	Wrong Content-Type. Rare for crawlers.
416	Range Not Satisfiable	Bad range request.
422	Unprocessable Content	Validation failed. API responses.
425	Too Early	Server refuses to process replayed request. Rare.
426	Upgrade Required	Server requires protocol upgrade.
428	Precondition Required	Server requires `If-Match` header.
429	Too Many Requests	Rate limited. Crawlers retry after `Retry-After` header value.
431	Request Header Fields Too Large	Headers too big. Rare.
451	Unavailable for Legal Reasons	GDPR-compliant geo-blocking. Crawlers respect this.

Code	Name	SEO meaning
500	Internal Server Error	Application bug. Investigate immediately. Sustained 5xx hurts rankings.
501	Not Implemented	Server doesn’t support the request.
502	Bad Gateway	Upstream server error.
503	Service Unavailable	Temporary. Use during maintenance with `Retry-After` header.
504	Gateway Timeout	Upstream timeout.
505	HTTP Version Not Supported	Wrong HTTP version. Rare.
506	Variant Also Negotiates	Configuration error. Rare.
507	Insufficient Storage	Out of disk space (WebDAV).
508	Loop Detected	Infinite recursion in content negotiation.
510	Not Extended	Further extensions required. Rare.
511	Network Authentication Required	Captive portal.

Use 301 for permanent content moves (95% of redirect cases)
Use 410 for intentionally deleted content (faster than 404 for de-indexing)
Use 503 with Retry-After during planned maintenance
Avoid 302 unless truly temporary (campaigns, A/B tests, auth redirects)
Monitor 5xx rate in Search Console — sustained errors reduce crawl rate and rankings