What are the HTTP status code classes?

1xx informational, 2xx success, 3xx redirection, 4xx client errors, and 5xx server errors.

What is the difference between 401 and 403?

401 means you are not authenticated; 403 means you are authenticated but not allowed.

When should I use 301 vs 302?

301 is a permanent redirect (passes SEO value); 302 is temporary.

What does a 429 status code mean?

429 Too Many Requests means the client has been rate-limited for sending too many requests in a window. The response should include a Retry-After header telling the client how long to wait before trying again.

What is the difference between 502 and 504?

502 Bad Gateway means a proxy or gateway received an invalid response from the upstream server, while 504 Gateway Timeout means the upstream did not respond in time. 502 is a bad reply; 504 is no reply at all.

When should I return 422 instead of 400?

Use 400 Bad Request when the request itself is malformed, such as broken JSON. Use 422 Unprocessable Entity when the syntax is fine but the data fails semantic validation, like an email that is well-formed but already taken.

HTTP Status Codes

Search or browse every HTTP status code by number or name, with a plain-English meaning and typical use case for each.

Updated June 2026

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Code	Name	Description	When to use
100	Continue	The server received the request headers and the client should proceed to send the request body.	Sent in response to an Expect: 100-continue header before a large upload.
101	Switching Protocols	The server is switching protocols as requested by the client via the Upgrade header.	Upgrading an HTTP connection to WebSocket.
102	Processing	The server has received and is processing the request, but no response is available yet (WebDAV).	Long-running WebDAV operations to prevent client timeouts.
103	Early Hints	Used to return preliminary headers (e.g. Link) before the final response.	Preloading resources while the server prepares the final response.
200	OK	The request succeeded. The meaning depends on the HTTP method.	Standard success response for GET, PUT, or POST that returns a body.
201	Created	The request succeeded and a new resource was created.	POST that creates a resource — include a Location header.
202	Accepted	The request has been accepted for processing, but processing is not complete.	Asynchronous or queued processing.
203	Non-Authoritative Information	The response is a transformed version from a proxy, not the origin.	Responses modified by a transforming proxy.
204	No Content	The request succeeded but there is no content to return.	Successful DELETE or PATCH with no response body.
205	Reset Content	Tells the client to reset the document view that sent the request.	Clearing a form after submission.
206	Partial Content	The server is delivering part of the resource due to a Range header.	Resumable downloads and media streaming.
207	Multi-Status	Conveys information about multiple resources in one response (WebDAV).	Batch WebDAV operations with mixed outcomes.
208	Already Reported	Members of a DAV binding already enumerated in a previous reply (WebDAV).	Avoiding repeated enumeration in WebDAV.
226	IM Used	The server fulfilled the request and the response is the result of instance manipulations.	Delta encoding responses.
300	Multiple Choices	The request has more than one possible response; the client should choose.	Content available in multiple formats.
301	Moved Permanently	The resource has permanently moved to a new URL.	Permanent redirects that pass SEO value.
302	Found	The resource is temporarily located at a different URL.	Temporary redirects (method may change to GET).
303	See Other	The client should retrieve the resource at another URL using GET.	Redirect after a POST to a confirmation page.
304	Not Modified	The cached version is still valid; no need to retransmit.	Conditional GET with If-None-Match or If-Modified-Since.
307	Temporary Redirect	The resource is temporarily at another URL; the method must not change.	Temporary redirect preserving the HTTP method.
308	Permanent Redirect	The resource is permanently at another URL; the method must not change.	Permanent redirect preserving the HTTP method.
400	Bad Request	The server cannot process the request due to a client error (malformed syntax).	Invalid request syntax or validation failure.
401	Unauthorized	Authentication is required and has failed or not been provided.	Missing or invalid credentials.
402	Payment Required	Reserved for future use; sometimes used by payment-gated APIs.	Indicating payment or quota is required.
403	Forbidden	The server understood the request but refuses to authorize it.	Authenticated but lacking permission.
404	Not Found	The server cannot find the requested resource.	Resource does not exist or URL is wrong.
405	Method Not Allowed	The HTTP method is not supported for the target resource.	POST to a read-only endpoint — include an Allow header.
406	Not Acceptable	No representation matches the Accept headers sent by the client.	Content negotiation failure.
407	Proxy Authentication Required	The client must authenticate with the proxy first.	Proxy requiring credentials.
408	Request Timeout	The server timed out waiting for the request.	Client too slow to send a complete request.
409	Conflict	The request conflicts with the current state of the resource.	Edit conflicts or uniqueness violations.
410	Gone	The resource is permanently gone and will not return.	Permanently removed content (better than 404 for SEO).
411	Length Required	The server requires a Content-Length header.	Rejecting requests without a content length.
412	Precondition Failed	A precondition in the request headers evaluated to false.	Conditional requests with If-Match that fail.
413	Payload Too Large	The request entity is larger than the server is willing to process.	Upload exceeding size limits.
414	URI Too Long	The requested URI is longer than the server can interpret.	Excessively long query strings.
415	Unsupported Media Type	The request media format is not supported by the resource.	Wrong Content-Type for an endpoint.
416	Range Not Satisfiable	The Range header cannot be fulfilled.	Requested byte range is outside the resource size.
417	Expectation Failed	The expectation in the Expect header cannot be met.	Failed Expect: 100-continue.
418	I'm a Teapot	The server refuses to brew coffee because it is a teapot (RFC 2324 joke).	An Easter egg; occasionally used for blocked requests.
422	Unprocessable Entity	The request is well-formed but contains semantic errors.	Validation errors on syntactically valid JSON.
423	Locked	The resource being accessed is locked (WebDAV).	WebDAV resource locking.
424	Failed Dependency	The request failed because a dependent request failed (WebDAV).	WebDAV operations that depend on a failed action.
425	Too Early	The server is unwilling to risk processing a request that might be replayed.	Preventing replay attacks in TLS early data.
426	Upgrade Required	The client should switch to a different protocol.	Requiring a TLS or protocol upgrade.
428	Precondition Required	The origin server requires the request to be conditional.	Preventing lost updates by requiring If-Match.
429	Too Many Requests	The user has sent too many requests in a given time (rate limiting).	Rate limiting — include a Retry-After header.
431	Request Header Fields Too Large	The header fields are too large for the server to process.	Oversized headers or cookies.
451	Unavailable For Legal Reasons	The resource is unavailable due to legal demands.	Content blocked by legal order or censorship.
500	Internal Server Error	A generic error occurred on the server.	Unhandled server-side exceptions.
501	Not Implemented	The server does not support the functionality required.	Unimplemented HTTP method or feature.
502	Bad Gateway	The server, acting as a gateway, received an invalid upstream response.	Upstream server failure behind a proxy or load balancer.
503	Service Unavailable	The server is not ready to handle the request (overload or maintenance).	Maintenance windows or overload — include Retry-After.
504	Gateway Timeout	The gateway did not get a timely response from the upstream server.	Upstream server too slow behind a proxy.
505	HTTP Version Not Supported	The HTTP version used in the request is not supported.	Rejecting unsupported protocol versions.
506	Variant Also Negotiates	Internal configuration error in content negotiation.	Misconfigured transparent negotiation.
507	Insufficient Storage	The server cannot store the representation needed (WebDAV).	WebDAV storage exhaustion.
508	Loop Detected	The server detected an infinite loop while processing (WebDAV).	WebDAV infinite loop prevention.
510	Not Extended	Further extensions to the request are required to fulfill it.	Required HTTP extensions are missing.
511	Network Authentication Required	The client must authenticate to gain network access.	Captive portals on public Wi-Fi.

The full list is bundled and searched in your browser — no requests are made.

How to use HTTP Status Codes

The HTTP Status Codes reference provides a searchable, filterable list of every standard HTTP response code from 1xx informational to 5xx server errors. Each entry includes the official name, a plain-English description, and practical guidance on when to use or expect the code. The full dataset is bundled locally — no network request needed to search.

Type a code number (e.g. 404) or keyword (e.g. "not found") in the search box to filter the list.
Use the class buttons (1xx, 2xx, 3xx, 4xx, 5xx) to filter by response category.
Click any row to expand the full description and usage guidance.
Use the search to quickly look up an unfamiliar status code during API debugging.

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HTTP status code classes

HTTP status codes are three-digit numbers grouped by their first digit. 1xx codes are informational — the request was received and is being processed (e.g. 100 Continue lets a client know it can send a request body). 2xx codes indicate success: 200 OK is the standard response, 201 Created confirms a new resource was made, 204 No Content confirms success with no body. 3xx codes are redirections: 301 Moved Permanently and 308 Permanent Redirect pass SEO equity; 302 and 307 are temporary. 4xx codes are client errors caused by bad requests: 400 Bad Request, 401 Unauthorized (not authenticated), 403 Forbidden (authenticated but not allowed), 404 Not Found. 5xx codes are server errors: 500 Internal Server Error, 502 Bad Gateway (upstream failure), 503 Service Unavailable (overloaded or maintenance).

HTTP status code classes overview
Class	Range	Meaning	Common examples
1xx	100–199	Informational	100 Continue, 101 Switching Protocols
2xx	200–299	Success	200 OK, 201 Created, 204 No Content
3xx	300–399	Redirection	301 Moved, 302 Found, 304 Not Modified
4xx	400–499	Client Error	400 Bad Request, 401 Unauthorized, 404 Not Found
5xx	500–599	Server Error	500 Internal Server Error, 503 Unavailable

Choosing the right status code for REST APIs

Returning the semantically correct status code matters for API clients, caches, and SEO crawlers. Use 201 Created (not 200) when a POST creates a new resource, and include a Location header pointing to it. Use 204 No Content for successful DELETE or PATCH with no response body. Distinguish 400 Bad Request (malformed syntax or validation failure) from 422 Unprocessable Entity (syntactically valid but semantically incorrect data). Use 401 only when authentication is missing or invalid — not when the user lacks permission (that is 403). Return 409 Conflict when a PUT would violate a uniqueness constraint. Use 429 Too Many Requests with a Retry-After header for rate limiting. Never use 200 with an error payload — this breaks client error detection and caching.

Worked examples

Look up 404

Inputs: 404

Result: Not Found — client error (4xx)

401 vs 403

Inputs: compare 401 and 403

Result: 401 = not authenticated · 403 = authenticated but forbidden

Rate limited

Inputs: 429

Result: Too Many Requests — send a Retry-After header

Glossary

HTTP: HyperText Transfer Protocol — the application-layer protocol for distributed, collaborative, hypermedia information systems.
Idempotent: A property of an HTTP method where multiple identical requests produce the same result as a single request; GET, PUT, DELETE are idempotent; POST is not.
Cache-Control: An HTTP header that directs caching behaviour; status codes 200, 301, and 410 are cacheable by default without Cache-Control.
Content negotiation: The mechanism by which a server selects the best representation for a response based on Accept headers; 406 Not Acceptable is returned when no match is found.
Rate limiting: Server-side enforcement of request quotas; properly indicated with 429 Too Many Requests and a Retry-After header.

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HTTP Status Codes

How to use HTTP Status Codes

HTTP status code classes

Choosing the right status code for REST APIs

Worked examples

Glossary

Related reading

Frequently Asked Questions

Why use HTTP Status Codes?

Common use cases

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