Error AtlasError Documentation and ResolutionHTTP documented errors
Browse HTTP status codes with plain-English explanations, troubleshooting context, and practical guidance for debugging API responses, browser requests, and server behavior.
This HTTP error reference is designed for users searching exact HTTP error messages, error codes, and clear how-to-fix guidance.
HTTP status code searches often start before a user even knows which application layer is responsible. A browser, API client, CDN, reverse proxy, or origin server may all surface the same status code for different reasons.
This hub keeps the protocol-level reference together so users can understand what each HTTP status code means first, then follow that context into the specific product, framework, or infrastructure issue causing it.
Authentication
Authentication errors
401 UnauthorizedHTTP 401 UnauthorizedThe request lacks valid authentication credentials for the target resource, so the server refused to authorize access.
403 ForbiddenHTTP 403 ForbiddenThe server understood the request but refuses to authorize it, even if the client retries with the same identity.
407 Proxy Authentication RequiredHTTP 407 Proxy Authentication RequiredThe request could not proceed because the client must first authenticate itself with the proxy.
Configuration
Configuration errors
General
General errors
100 ContinueHTTP 100 ContinueThe server has received the request headers and the client should continue sending the request body or proceed with the request.
101 Switching ProtocolsHTTP 101 Switching ProtocolsThe server is switching protocols as requested by the client, usually after an Upgrade header negotiation.
102 ProcessingHTTP 102 ProcessingThe server has received the request and is processing it, but no final response is available yet.
103 Early HintsHTTP 103 Early HintsThe server is sending preliminary response headers so the client can begin loading linked resources before the final response is ready.
104 Upload Resumption SupportedHTTP 104 Upload Resumption SupportedThe server indicates temporary support for resumable upload behavior defined by the current extension draft.
200 OKHTTP 200 OKThe request succeeded and the server returned the requested representation or confirmation of the successful action.
201 CreatedHTTP 201 CreatedThe request succeeded and created a new resource.
202 AcceptedHTTP 202 AcceptedThe server accepted the request for processing, but the work has not completed yet.
203 Non-Authoritative InformationHTTP 203 Non-Authoritative InformationThe server successfully returned a response, but the metadata may have been modified by a transforming proxy.
204 No ContentHTTP 204 No ContentThe request succeeded, but the server has no response body to return.
205 Reset ContentHTTP 205 Reset ContentThe request succeeded and the client should reset the document view or form that triggered the request.
206 Partial ContentHTTP 206 Partial ContentThe server is returning only the requested part of the resource, usually in response to a Range request.
207 Multi-StatusHTTP 207 Multi-StatusThe response contains status information for multiple independent operations or resources.
208 Already ReportedHTTP 208 Already ReportedThe response avoids repeating the same DAV binding information that was already reported earlier in the same multistatus response.
226 IM UsedHTTP 226 IM UsedThe server completed the request and applied one or more instance manipulations to the representation.
300 Multiple ChoicesHTTP 300 Multiple ChoicesThe requested resource has multiple possible representations or locations, and the client must choose one.
301 Moved PermanentlyHTTP 301 Moved PermanentlyThe resource has been permanently moved to a new URL.
302 FoundHTTP 302 FoundThe resource is temporarily available at a different URL.
303 See OtherHTTP 303 See OtherThe server directs the client to retrieve the result of the request from another URL using GET.
304 Not ModifiedHTTP 304 Not ModifiedThe resource has not changed since the client's conditional request, so the cached version can be reused.
305 Use ProxyHTTP 305 Use ProxyThe requested resource must be accessed through the proxy identified in the response.
306 UnusedHTTP 306 UnusedThis status code is reserved and currently unused.
307 Temporary RedirectHTTP 307 Temporary RedirectThe resource is temporarily available at another URL and the client must preserve the original request method.
308 Permanent RedirectHTTP 308 Permanent RedirectThe resource has moved permanently and the client must preserve the original request method when following the redirect.
400 Bad RequestHTTP 400 Bad RequestThe server rejected the request because it considers the request malformed or invalid and will not process it as sent.
402 Payment RequiredHTTP 402 Payment RequiredThe request cannot be completed until payment-related conditions are met.
404 Not FoundHTTP 404 Not FoundThe server cannot find the requested resource at the given URL, though it does not necessarily indicate whether the absence is temporary or permanent.
406 Not AcceptableHTTP 406 Not AcceptableThe server cannot produce a response matching the list of acceptable values defined in the request's proactive content negotiation headers.
410 GoneHTTP 410 GoneThe server indicates that the requested resource has been permanently removed and is not expected to return.
411 Length RequiredHTTP 411 Length RequiredThe server refused to accept the request because it requires a valid Content-Length header.
412 Precondition FailedHTTP 412 Precondition FailedThe server rejected the request because one or more conditions defined by conditional request headers evaluated to false.
415 Unsupported Media TypeHTTP 415 Unsupported Media TypeThe server refused the request because the payload format is in an unsupported media type.
416 Range Not SatisfiableHTTP 416 Range Not SatisfiableThe requested byte range cannot be served for the target resource.
417 Expectation FailedHTTP 417 Expectation FailedThe server cannot meet the expectation given in the request Expect header.
418 UnusedHTTP 418 UnusedThis status code is reserved and currently unused in the IANA registry.
421 Misdirected RequestHTTP 421 Misdirected RequestThe request was directed to a server that is not able to produce a response for the target URI.
422 Unprocessable ContentHTTP 422 Unprocessable ContentThe server understood the content type and syntax of the request, but could not process the contained instructions.
423 LockedHTTP 423 LockedThe target resource is locked and cannot be modified or accessed in the requested way until the lock is released.
424 Failed DependencyHTTP 424 Failed DependencyThe current request failed because it depended on another action that did not succeed.
425 Too EarlyHTTP 425 Too EarlyThe server is unwilling to risk processing a request that might be replayed too early.
426 Upgrade RequiredHTTP 426 Upgrade RequiredThe server refuses to perform the request using the current protocol and requires the client to upgrade.
428 Precondition RequiredHTTP 428 Precondition RequiredThe origin server requires the request to be conditional to prevent lost updates.
431 Request Header Fields Too LargeHTTP 431 Request Header Fields Too LargeThe server is unwilling to process the request because the request header fields are too large, either individually or in total.
451 Unavailable For Legal ReasonsHTTP 451 Unavailable For Legal ReasonsThe server is denying access to the resource because of a legal demand or policy-based legal restriction.
501 Not ImplementedHTTP 501 Not ImplementedThe server does not support the functionality required to fulfill the request.
505 HTTP Version Not SupportedHTTP 505 HTTP Version Not SupportedThe server does not support, or refuses to support, the major HTTP version used in the request message.
506 Variant Also NegotiatesHTTP 506 Variant Also NegotiatesThe server has an internal configuration error involving transparent content negotiation for the chosen variant.
507 Insufficient StorageHTTP 507 Insufficient StorageThe server cannot store the representation needed to complete the request.
508 Loop DetectedHTTP 508 Loop DetectedThe server terminated an operation because it encountered an infinite loop while processing the request.
510 Not ExtendedHTTP 510 Not ExtendedThe server requires further extensions to the request before it can fulfill it; this code is now marked obsoleted in the registry.
511 Network Authentication RequiredHTTP 511 Network Authentication RequiredThe client must authenticate to gain network access, often through a captive portal or intermediary.
Networking
Networking errors
408 Request TimeoutHTTP 408 Request TimeoutThe server timed out waiting for the client to send a complete request in the allowed time window.
413 Content Too LargeHTTP 413 Content Too LargeThe server refused to process the request because the request body is larger than the server is willing or able to handle.
414 URI Too LongHTTP 414 URI Too LongThe server refused the request because the target URI is longer than the server is willing to interpret.
429 Too Many RequestsHTTP 429 Too Many RequestsThe client sent too many requests in a given time window and the server rate-limited further access temporarily.
502 Bad GatewayHTTP 502 Bad GatewayA server acting as a gateway or proxy received an invalid response from the upstream server it depends on.
504 Gateway TimeoutHTTP 504 Gateway TimeoutA gateway or proxy server did not receive a timely response from the upstream server it needed to complete the request.
Runtime
Runtime errors
500 Internal Server ErrorHTTP 500 Internal Server ErrorThe server encountered an unexpected condition that prevented it from fulfilling the request.
503 Service UnavailableHTTP 503 Service UnavailableThe server is temporarily unable to handle the request, often because it is overloaded or down for maintenance.