HTTP Status Codes — Complete Reference Guide
66 HTTP status codes explained with causes, impact, and solutions for developers and server administrators. Covers standard RFC codes and Cloudflare-specific error codes.
4
1xx
9
2xx
7
3xx
28
4xx
18
5xx
0
Cloudflare
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1xx Informational4 codes
Provisional responses indicating the request was received and processing continues.
2xx Success9 codes
The request was successfully received, understood, and accepted.
3xx Redirection7 codes
Further action is needed to complete the request, usually a redirect to another URL.
4xx Client Error28 codes
The request contains bad syntax or cannot be fulfilled by the server.
400Bad RequestMedium401UnauthorizedHigh402Payment RequiredMedium403ForbiddenHigh404Not FoundMedium405Method Not AllowedMedium406Not AcceptableMedium407Proxy Authentication RequiredHigh408Request TimeoutMedium409ConflictMedium410GoneMedium411Length RequiredMedium412Precondition FailedMedium413Payload Too LargeMedium414URI Too LongMedium415Unsupported Media TypeMedium416Range Not SatisfiableMedium418I'm a TeapotLow421Misdirected RequestMedium422Unprocessable EntityMedium423LockedMedium424Failed DependencyMedium425Too EarlyMedium426Upgrade RequiredMedium428Precondition RequiredMedium429Too Many RequestsHigh431Request Header Fields Too LargeMedium451Unavailable For Legal ReasonsHigh
5xx Server Error18 codes
The server failed to fulfill a valid request due to an internal error.
500Internal Server ErrorCritical501Not ImplementedHigh502Bad GatewayCritical503Service UnavailableCritical504Gateway TimeoutCritical505HTTP Version Not SupportedHigh506Variant Also NegotiatesMedium507Insufficient StorageCritical508Loop DetectedHigh510Not ExtendedMedium511Network Authentication RequiredHigh520Web Server Returns Unknown ErrorCritical521Web Server Is DownCritical522Connection Timed OutCritical523Origin Is UnreachableCritical524A Timeout OccurredCritical525SSL Handshake FailedCritical526Invalid SSL CertificateCritical
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Frequently Asked Questions
What are HTTP status codes?
HTTP status codes are three-digit numbers returned by a web server in response to a client's request. They indicate whether the request was successful, redirected, or resulted in an error. Status codes are grouped into five classes: 1xx (Informational), 2xx (Success), 3xx (Redirection), 4xx (Client Error), and 5xx (Server Error).
What is the most common HTTP error code?
The most common HTTP error code is 404 Not Found, which means the requested page doesn't exist on the server. Other frequently encountered errors include 500 Internal Server Error, 403 Forbidden, 502 Bad Gateway, and 503 Service Unavailable.
What's the difference between a 301 and 302 redirect?
A 301 redirect is permanent — it tells browsers and search engines that the page has permanently moved to a new URL. A 302 redirect is temporary — the original URL should still be used for future requests. For SEO, 301 redirects pass link equity to the new URL, while 302 redirects do not.
How do I fix HTTP 500 Internal Server Error?
HTTP 500 is a generic server-side error. Check the server error logs for specific details. Common fixes include: checking file permissions, reviewing .htaccess rules, increasing PHP memory limits, checking database connections, and reviewing recent code changes.
What are Cloudflare 5xx errors?
Cloudflare 520-526 errors are custom codes that indicate communication problems between Cloudflare's CDN and the origin web server. They are not standard HTTP codes. Common causes include origin server crashes, SSL configuration issues, or the origin server blocking Cloudflare IPs.