HTTP status codes by class
Standard codes link to the RFC that defines them. Codes used only by Cloudflare or nginx are marked non-standard. The label on each row says whether an Uptimecheck HTTP monitor counts the code as up or down with its default settings (200–399 is up).
No status code matches. Try a number such as 404, or a word such as “timeout”. Show all codes
1xx Informational
Interim responses: the request is under way and the real answer follows.
- 100 Continue The server got the request headers and the client may send the body. Monitor: Interim
- 101 Switching Protocols The server agrees to switch the connection to another protocol. Monitor: Down
- 102 Processing Deprecated A WebDAV server is still working on a long request. Monitor: Interim
- 103 Early Hints The server sends preload hints before the final response is ready. Monitor: Interim
2xx Success
The request was received, understood and accepted.
- 200 OK The request succeeded. Monitor: Up
- 201 Created The request created a new resource. Monitor: Up
- 202 Accepted The request was accepted but hasn’t been processed yet. Monitor: Up
- 203 Non-Authoritative Information The request succeeded, but a proxy changed the content. Monitor: Up
- 204 No Content The request succeeded and there is no body to send. Monitor: Up
- 205 Reset Content The request succeeded and the client should reset the form that sent it. Monitor: Up
- 206 Partial Content The server sends only the part of the file the client asked for. Monitor: Up
- 207 Multi-Status One WebDAV response holds a separate status for several resources. Monitor: Up
- 208 Already Reported WebDAV members were already listed earlier in the same response. Monitor: Up
- 226 IM Used The server answered with changes to a version the client already has. Monitor: Up
3xx Redirection
The client has to go somewhere else to complete the request.
- 300 Multiple Choices The resource has several versions and the client may pick one. Monitor: Up
- 301 Moved Permanently The page has moved to a new URL for good. Monitor: Up
- 302 Found The page is temporarily at another URL. Monitor: Up
- 303 See Other The client should get the result from another URL with a GET. Monitor: Up
- 304 Not Modified The copy the client already has is still current. Monitor: Up
- 305 Use Proxy Deprecated A deprecated code that told the client to use a proxy. Monitor: Up
- 306 (Unused) Reserved, not used A reserved code that is no longer used. Monitor: Up
- 307 Temporary Redirect The page is temporarily elsewhere and the method must be kept. Monitor: Up
- 308 Permanent Redirect The page has moved for good and the method must be kept. Monitor: Up
4xx Client error
The server is up, but refuses the request as it was sent.
- 400 Bad Request The server won’t process a request it sees as malformed. Monitor: Down
- 401 Unauthorized The request needs valid authentication. Monitor: Down
- 402 Payment Required A code reserved for future use, used by some services for unpaid accounts. Monitor: Down
- 403 Forbidden The server understood the request but refuses it. Monitor: Down
- 404 Not Found The server has nothing at this URL. Monitor: Down
- 405 Method Not Allowed The URL exists but doesn’t accept this request method. Monitor: Down
- 406 Not Acceptable The server can’t answer in a format the client accepts. Monitor: Down
- 407 Proxy Authentication Required A proxy between the client and the server needs credentials. Monitor: Down
- 408 Request Timeout The server gave up waiting for the client to send the request. Monitor: Down
- 409 Conflict The request conflicts with the resource’s current state. Monitor: Down
- 410 Gone The page has been removed for good. Monitor: Down
- 411 Length Required The server requires a Content-Length header. Monitor: Down
- 412 Precondition Failed A condition in the request headers turned out false. Monitor: Down
- 413 Content Too Large The request body is larger than the server accepts. Monitor: Down
- 414 URI Too Long The URL is longer than the server will read. Monitor: Down
- 415 Unsupported Media Type The server doesn’t accept the format of the request body. Monitor: Down
- 416 Range Not Satisfiable The requested part of the file doesn’t exist. Monitor: Down
- 417 Expectation Failed The server can’t meet the request’s Expect header. Monitor: Down
- 418 (Unused) Reserved, not used The reserved “I’m a teapot” code from an April Fools’ RFC. Monitor: Down
- 421 Misdirected Request The request reached a server that can’t answer for this host name. Monitor: Down
- 422 Unprocessable Content The request is well-formed but its content isn’t valid. Monitor: Down
- 423 Locked The WebDAV resource is locked. Monitor: Down
- 424 Failed Dependency A WebDAV action failed because another one it depended on failed. Monitor: Down
- 425 Too Early The server won’t risk processing a request that could be replayed. Monitor: Down
- 426 Upgrade Required The server requires the client to switch to another protocol. Monitor: Down
- 428 Precondition Required The server requires a conditional request. Monitor: Down
- 429 Too Many Requests The client sent too many requests in a given time. Monitor: Down
- 431 Request Header Fields Too Large The request headers are too large for the server. Monitor: Down
- 444 No Response Non-standard · nginx Nginx closed the connection without sending anything. Monitor: Down
- 451 Unavailable For Legal Reasons Access is denied because of a legal demand. Monitor: Down
- 499 Client Closed Request Non-standard · nginx The client hung up before nginx could answer. Monitor: Interim
5xx Server error
The server, or something in front of it, failed to answer the request.
- 500 Internal Server Error The server hit an unexpected error. Monitor: Down
- 501 Not Implemented The server doesn’t support what the request needs. Monitor: Down
- 502 Bad Gateway A proxy got an invalid response from the server behind it. Monitor: Down
- 503 Service Unavailable The server is temporarily overloaded or down for maintenance. Monitor: Down
- 504 Gateway Timeout A proxy didn’t get an answer from the server behind it in time. Monitor: Down
- 505 HTTP Version Not Supported The server doesn’t support the request’s HTTP version. Monitor: Down
- 506 Variant Also Negotiates The server’s content negotiation is misconfigured. Monitor: Down
- 507 Insufficient Storage The server has no room to store what the request needs. Monitor: Down
- 508 Loop Detected The server found an infinite loop while processing the request. Monitor: Down
- 510 Not Extended Obsolete An obsolete code from the HTTP extension framework. Monitor: Down
- 511 Network Authentication Required The network needs you to sign in before you get access. Monitor: Down
- 520 Web Server Returned an Unknown Error Non-standard · Cloudflare Cloudflare got an empty or unexpected response from the origin server. Monitor: Down
- 521 Web Server Is Down Non-standard · Cloudflare The origin server refused Cloudflare’s connection. Monitor: Down
- 522 Connection Timed Out Non-standard · Cloudflare Cloudflare couldn’t connect to the origin server in time. Monitor: Down
- 523 Origin Is Unreachable Non-standard · Cloudflare Cloudflare can’t reach the origin server at all. Monitor: Down
- 524 A Timeout Occurred Non-standard · Cloudflare The origin server accepted the connection but answered too slowly. Monitor: Down
- 525 SSL Handshake Failed Non-standard · Cloudflare The TLS handshake between Cloudflare and the origin failed. Monitor: Down
- 526 Invalid SSL Certificate Non-standard · Cloudflare Cloudflare couldn’t validate the origin server’s certificate. Monitor: Down
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The status codes that matter for uptime, which ones mean real trouble and how to set up checks that don’t cry wolf.
Read the cheat sheetQuestions
What do the five classes of status codes mean?
The first digit gives the class: 1xx informational (the request is under way), 2xx success, 3xx redirection, 4xx client error (the server refuses the request as sent) and 5xx server error. A client that doesn’t know a code treats it like the x00 code of its class, so an unknown 4xx is handled as a 400.
Which status codes does Uptimecheck count as down?
By default an HTTP monitor counts 200–399 as up and anything else as down, and an outage is only reported once a second check confirms it. Redirects are followed, up to 10, and the final answer decides. You can set the expected status codes for each monitor, for example 200-299, 401. The free Is it down? checker counts any answer below 500 as the site answering.
What is the difference between 502, 503 and 504?
All three usually come from a proxy or load balancer in front of the application. 502 Bad Gateway: the server behind it gave an invalid answer or none, often because it crashed. 503 Service Unavailable: the server is overloaded or in maintenance and says so. 504 Gateway Timeout: the server behind it didn’t answer in time.
Are Cloudflare’s 52x codes and nginx’s 444 and 499 standard?
No. Cloudflare sends 520–526 to describe problems between its network and the origin server, and nginx uses 444 (close the connection without answering) and 499 (the client hung up) in its own logs. They aren’t in any RFC, so they are marked non-standard here.
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