Interactive HTTP Status Code Reference & Diagnostic Guide
The problem: Debugging API errors requires quick, accurate lookups of subtle distinction pairs (401 vs 403, 502 vs 504) without navigating dense RFC specs.
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Interactive HTTP Status Code Reference & Diagnostic Guide: the complete guide
The Interactive HTTP Status Code Reference and Diagnostic Guide provides instant search, RFC specifications, and debugging protocols for all standard IETF HTTP response status codes (1xx Informational, 2xx Success, 3xx Redirection, 4xx Client Error, 5xx Server Error). Search by numeric code or keyword to diagnose API failures, configure reverse proxies, and implement RESTful routing conventions.
The Five Core HTTP Response Classes
HTTP status codes are three-digit integers grouped into five distinct semantic classes defined by RFC 9110. 1xx codes indicate provisional informational responses; 2xx codes confirm that client requests were successfully received, understood, and accepted; 3xx codes instruct user agents to take further action to complete the request (redirection); 4xx codes pinpoint client-side errors (such as authentication failures or missing resources); and 5xx codes signal that a server encountered an error while attempting to fulfill a valid request.
Proper semantic code selection is essential for search engine indexing, client-side caching strategies, and automated monitoring systems.
Debugging Crucial Edge Cases: 401 vs. 403, 502 vs. 504
Developers frequently confuse subtle distinction pairs. A 401 Unauthorized denotes missing or invalid authentication credentials (you are unauthenticated and must log in), whereas a 403 Forbidden means the server recognizes your identity but refuses access based on insufficient permissions (you are unauthorized).
Similarly, a 502 Bad Gateway means an edge proxy received an invalid response from an upstream server, while a 504 Gateway Timeout signifies that the upstream server failed to respond within the configured timeout window. Our guide details exact debugging runbooks for each error.
Step by step: how to use HTTP Status Codes
1
Type a status code (e.g., '404', '502') or descriptive term (e.g., 'timeout', 'forbidden') in the search box.
2
Filter codes quickly using the 1xx, 2xx, 3xx, 4xx, and 5xx category pills.
3
Click any status code card to expand its full RFC documentation, header requirements, and caching behavior.
4
Review the practical debugging tips detailing common real-world triggers in Nginx, AWS, and Node.js.
5
Copy code names and descriptions directly for pull request reviews and documentation.
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60 of 60 codes
100Continue
1xx Informational
The server has received the request headers and the client should proceed to send the request body.
RFCRFC 7231
Use CaseLarge file uploads where client checks if server is ready before sending body.
101Switching Protocols
1xx Informational
The requester has asked the server to switch protocols and the server has agreed to do so.
RFCRFC 7231
Use CaseWebSocket upgrade handshake (HTTP → WS).
102Processing
1xx Informational
The server has received and is processing the request, but no response is available yet.
RFCRFC 2518 (WebDAV)
Use CaseLong-running WebDAV operations.
103Early Hints
1xx Informational
Primarily used with the Link header to allow the user agent to start preloading resources.
RFCRFC 8297
Use CasePreloading CSS/fonts while the server prepares the full response.
200OK
2xx Success
The request succeeded. The meaning of success depends on the HTTP method used.
RFCRFC 7231
Use CaseStandard successful GET, POST, PUT, PATCH responses.
201Created
2xx Success
The request succeeded and a new resource was created as a result.
RFCRFC 7231
Use CasePOST to create a new record; response includes Location header.
202Accepted
2xx Success
The request has been received but not yet acted upon. It is non-committal.
RFCRFC 7231
Use CaseAsync job queuing — request accepted for background processing.
203Non-Authoritative Information
2xx Success
The returned metadata is not exactly the same as is available from the origin server.
RFCRFC 7231
Use CaseProxy or mirror server returning transformed content.
204No Content
2xx Success
There is no content to send for this request, but the headers may be useful.
RFCRFC 7231
Use CaseDELETE operations; successful updates with no body needed.
205Reset Content
2xx Success
Tells the user agent to reset the document which sent this request.
RFCRFC 7231
Use CaseForm submission — signals client to clear the form.
206Partial Content
2xx Success
This response code is used when the Range header is sent from the client to request only part of a resource.
RFCRFC 7233
Use CaseVideo streaming, resumable downloads (byte-range requests).
207Multi-Status
2xx Success
Conveys information about multiple resources, for situations where multiple status codes might be appropriate.
RFCRFC 4918 (WebDAV)
Use CaseWebDAV operations affecting multiple files simultaneously.
208Already Reported
2xx Success
Used inside a <dav:propstat> response element to avoid enumerating the internal members of multiple bindings.
RFCRFC 5842 (WebDAV)
Use CaseWebDAV — avoid repeating members already enumerated.
226IM Used
2xx Success
The server has fulfilled a GET request for the resource and the response is a representation of the result of one or more instance-manipulations applied to the current instance.
RFCRFC 3229
Use CaseHTTP delta encoding — sending diffs instead of full resources.
300Multiple Choices
3xx Redirection
The request has more than one possible response. The user or user agent should choose one of them.
RFCRFC 7231
Use CaseContent negotiation — multiple formats available (JSON, XML).
301Moved Permanently
3xx Redirection
The URL of the requested resource has been changed permanently. The new URL is given in the response.
RFCRFC 7231
Use CaseDomain migration, URL restructuring — SEO-safe permanent redirect.
302Found
3xx Redirection
This response code means that the URI of requested resource has been changed temporarily.
RFCRFC 7231
Use CaseTemporary redirects; preserves original URL for indexing.
303See Other
3xx Redirection
The server sent this response to direct the client to get the requested resource at another URI with a GET request.
RFCRFC 7231
Use CasePost/Redirect/Get pattern after form submission.
304Not Modified
3xx Redirection
This is used for caching purposes. It tells the client that the response has not been modified.
RFCRFC 7232
Use CaseBrowser cache validation — ETag or Last-Modified match.
307Temporary Redirect
3xx Redirection
The server sends this response to direct the client to get the requested resource at another URI with same method that was used in the prior request.
RFCRFC 7231
Use CaseTemporary redirect preserving HTTP method (POST stays POST).
308Permanent Redirect
3xx Redirection
This means that the resource is now permanently located at another URI, specified by the Location HTTP response header.
RFCRFC 7538
Use CasePermanent redirect preserving HTTP method — HTTPS enforcement.
400Bad Request
4xx Client Error
The server cannot or will not process the request due to something that is perceived to be a client error.
RFCRFC 7231
Use CaseMalformed JSON body, missing required fields, invalid query params.
401Unauthorized
4xx Client Error
Although the HTTP standard specifies 'unauthorized', semantically this response means 'unauthenticated'.
RFCRFC 7235
Use CaseMissing or invalid authentication token (Bearer, API key).
402Payment Required
4xx Client Error
Reserved for future use. Originally created to be used as part of a digital cash payment system.
RFCRFC 7231
Use CaseSaaS quota exceeded, subscription-gated API endpoints.
403Forbidden
4xx Client Error
The client does not have access rights to the content; unlike 401, the client's identity is known to the server.
RFCRFC 7231
Use CaseAuthenticated user lacks permission for requested resource.
404Not Found
4xx Client Error
The server cannot find the requested resource. In the browser, this means the URL is not recognized.
RFCRFC 7231
Use CaseMissing pages, deleted records, typo in API endpoint path.
405Method Not Allowed
4xx Client Error
The request method is known by the server but is not supported by the target resource.
RFCRFC 7231
Use CaseSending DELETE to a read-only endpoint.
406Not Acceptable
4xx Client Error
Server can't produce a response matching the list of acceptable values defined in the request's proactive content negotiation headers.
RFCRFC 7231
Use CaseAPI only returns JSON but client requests XML via Accept header.
407Proxy Authentication Required
4xx Client Error
This is similar to 401 but authentication is needed to be done by a proxy.
RFCRFC 7235
Use CaseCorporate proxy requiring authentication credentials.
408Request Timeout
4xx Client Error
This response is sent on an idle connection by some servers, even without any previous request by the client.
RFCRFC 7231
Use CaseClient took too long to send the full request body.
409Conflict
4xx Client Error
This response is sent when a request conflicts with the current state of the server.
RFCRFC 7231
Use CaseDuplicate record creation, optimistic concurrency conflict.
410Gone
4xx Client Error
This response is sent when the requested content has been permanently deleted from server, with no forwarding address.
RFCRFC 7231
Use CasePermanently removed resources — tells crawlers to deindex.
411Length Required
4xx Client Error
Server rejected the request because the Content-Length header field is not defined and the server requires it.
RFCRFC 7231
Use CaseMissing Content-Length header on POST/PUT with body.
412Precondition Failed
4xx Client Error
The client has indicated preconditions in its headers which the server does not meet.
RFCRFC 7232
Use CaseIf-Match / If-None-Match conditional request validation failed.
413Content Too Large
4xx Client Error
Request entity is larger than limits defined by server. The server might close the connection or return a Retry-After header.
RFCRFC 7231
Use CaseFile upload exceeding server's max payload size limit.
414URI Too Long
4xx Client Error
The URI requested by the client is longer than the server is willing to interpret.
RFCRFC 7231
Use CaseOverly long query strings or GET parameters.
415Unsupported Media Type
4xx Client Error
The media format of the requested data is not supported by the server, so the server is rejecting the request.
RFCRFC 7231
Use CaseSending text/plain to an API that only accepts application/json.
416Range Not Satisfiable
4xx Client Error
The range specified by the Range header field in the request cannot be fulfilled.
RFCRFC 7233
Use CaseRequested byte range falls outside the file size.
417Expectation Failed
4xx Client Error
This response code means the expectation indicated by the Expect request header field cannot be met by the server.
RFCRFC 7231
Use CaseExpect: 100-continue header that the server cannot fulfill.
418I'm a teapot
4xx Client Error
The server refuses the attempt to brew coffee with a teapot. This error is a reference to Hyper Text Coffee Pot Control Protocol.
RFCRFC 2324
Use CaseEaster egg status code; sometimes used for intentional rejections.
422Unprocessable Content
4xx Client Error
The request was well-formed but was unable to be followed due to semantic errors.
RFCRFC 4918 / RFC 9110
Use CaseValid JSON syntax but invalid field values (e.g., negative age).
423Locked
4xx Client Error
The resource that is being accessed is locked.
RFCRFC 4918 (WebDAV)
Use CaseWebDAV file locked for editing by another user.
424Failed Dependency
4xx Client Error
The request failed due to failure of a previous request.
RFCRFC 4918 (WebDAV)
Use CaseWebDAV batch operation where a prerequisite action failed.
425Too Early
4xx Client Error
Indicates that the server is unwilling to risk processing a request that might be replayed.
RFCRFC 8470
Use CaseTLS 1.3 Early Data (0-RTT) replay protection.
426Upgrade Required
4xx Client Error
The server refuses to perform the request using the current protocol but might be willing to do so after the client upgrades.
RFCRFC 7231
Use CaseServer requires TLS upgrade before processing the request.
428Precondition Required
4xx Client Error
The origin server requires the request to be conditional.
RFCRFC 6585
Use CaseForce clients to use conditional requests to prevent lost updates.
429Too Many Requests
4xx Client Error
The user has sent too many requests in a given amount of time ('rate limiting').
RFCRFC 6585
Use CaseAPI rate limiting — client exceeded request quota.
431Request Header Fields Too Large
4xx Client Error
The server is unwilling to process the request because its header fields are too large.
RFCRFC 6585
Use CaseExcessive cookies or very large Authorization headers.
451Unavailable For Legal Reasons
4xx Client Error
The user agent requested a resource that cannot legally be provided.
RFCRFC 7725
Use CaseGDPR content blocks, DMCA takedowns, government censorship.
500Internal Server Error
5xx Server Error
The server has encountered a situation it does not know how to handle.
RFCRFC 7231
Use CaseUnhandled exceptions, database errors, crash in application code.
501Not Implemented
5xx Server Error
The request method is not supported by the server and cannot be handled.
RFCRFC 7231
Use CaseServer doesn't support the HTTP method (e.g., PATCH not implemented).
502Bad Gateway
5xx Server Error
This error response means that the server, while working as a gateway to get a response needed to handle the request, got an invalid response.
RFCRFC 7231
Use CaseReverse proxy received invalid response from upstream server.
503Service Unavailable
5xx Server Error
The server is not ready to handle the request. Common causes are a server that is down for maintenance or that is overloaded.
RFCRFC 7231
Use CaseDeployment maintenance window, server overload, health check failure.
504Gateway Timeout
5xx Server Error
This error response is given when the server is acting as a gateway and cannot get a response in time.
RFCRFC 7231
Use CaseLoad balancer timed out waiting for slow upstream service.
505HTTP Version Not Supported
5xx Server Error
The HTTP version used in the request is not supported by the server.
RFCRFC 7231
Use CaseClient using HTTP/3 on a server that only supports HTTP/1.1.
506Variant Also Negotiates
5xx Server Error
The server has an internal configuration error.
RFCRFC 2295
Use CaseTransparent content negotiation misconfiguration.
507Insufficient Storage
5xx Server Error
The method could not be performed on the resource because the server is unable to store the representation needed to successfully complete the request.
RFCRFC 4918 (WebDAV)
Use CaseWebDAV — server disk full, cannot store uploaded file.
508Loop Detected
5xx Server Error
The server detected an infinite loop while processing the request.
RFCRFC 5842 (WebDAV)
Use CaseWebDAV infinite loop in resource traversal.
510Not Extended
5xx Server Error
Further extensions to the request are required for the server to fulfill it.
RFCRFC 2774
Use CaseHTTP Extension Framework — mandatory extension not present.
511Network Authentication Required
5xx Server Error
Indicates that the client needs to authenticate to gain network access.
RFCRFC 6585
Use CaseCaptive portal — hotel/airport WiFi login required.