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HTTP Status Code Reference

HTTP status code reference with searchable definitions and practical use cases for 1xx informational, 2xx success, 3xx redirection, 4xx client error, and 5xx server error.

Total

1xx

2xx

3xx

4xx

5xx

Code	Title	Class	Description	Typical use
1xx Informational · 100~103
100	Continue	1xx Informational	Request headers received, continue sending body.	Large upload handshakes
101	Switching Protocols	1xx Informational	Server is switching protocols as requested.	WebSocket upgrade
102	Processing	1xx Informational	Server accepted but is still processing.	Long-running WebDAV operations
103	Early Hints	1xx Informational	Preliminary response with link hints.	Preload assets early
2xx Success · 200~206
200	OK	2xx Success	Request succeeded.	Standard API or page response
201	Created	2xx Success	Resource created successfully.	POST create endpoints
202	Accepted	2xx Success	Accepted for async processing.	Queue-based workflows
204	No Content	2xx Success	Success with no response body.	DELETE or idempotent updates
206	Partial Content	2xx Success	Partial range response.	Media streaming and resume download
3xx Redirection · 300~308
300	Multiple Choices	3xx Redirection	Multiple representations available.	Variant negotiation
301	Moved Permanently	3xx Redirection	Permanent redirect to new URL.	Canonical URL migration
302	Found	3xx Redirection	Temporary redirect.	Short-lived relocation
303	See Other	3xx Redirection	Redirect to retrieval endpoint.	Post/Redirect/Get pattern
304	Not Modified	3xx Redirection	Cached version is still valid.	Conditional requests with ETag
307	Temporary Redirect	3xx Redirection	Temporary redirect preserving method.	Safe temporary reroute
308	Permanent Redirect	3xx Redirection	Permanent redirect preserving method.	Strict migration of APIs
4xx Client Error · 400~451
400	Bad Request	4xx Client Error	Invalid request syntax or payload.	Schema validation failures
401	Unauthorized	4xx Client Error	Authentication required or invalid.	Missing/invalid token
403	Forbidden	4xx Client Error	Authenticated but not allowed.	Role or policy denial
404	Not Found	4xx Client Error	Resource not found.	Unknown route or identifier
405	Method Not Allowed	4xx Client Error	HTTP method not supported.	Wrong verb on endpoint
406	Not Acceptable	4xx Client Error	No acceptable representation available.	Content negotiation mismatch
408	Request Timeout	4xx Client Error	Client took too long.	Idle client connection
409	Conflict	4xx Client Error	Request conflicts with current state.	Versioning or duplicate conflict
410	Gone	4xx Client Error	Resource permanently removed.	Intentional endpoint retirement
412	Precondition Failed	4xx Client Error	Conditional header precondition failed.	If-Match mismatch
413	Payload Too Large	4xx Client Error	Request body exceeds limit.	Upload size enforcement
414	URI Too Long	4xx Client Error	Request URI is too long.	Oversized query string
415	Unsupported Media Type	4xx Client Error	Content type not supported.	Invalid upload media type
418	I'm a teapot	4xx Client Error	RFC joke code, rarely used in prod.	Debug/easter egg responses
421	Misdirected Request	4xx Client Error	Request sent to wrong server.	HTTP/2 authority mismatch
422	Unprocessable Content	4xx Client Error	Well-formed but semantic errors.	Business rule validation errors
425	Too Early	4xx Client Error	Server unwilling to risk replay.	Early data replay protection
426	Upgrade Required	4xx Client Error	Client must switch protocol.	Require TLS or newer protocol
428	Precondition Required	4xx Client Error	Server requires conditional request.	Lost-update prevention
429	Too Many Requests	4xx Client Error	Rate limit exceeded.	Throttle abusive traffic
431	Request Header Fields Too Large	4xx Client Error	Headers exceed acceptable size.	Oversized cookies/headers
451	Unavailable For Legal Reasons	4xx Client Error	Blocked by legal requirement.	Compliance takedown restrictions
5xx Server Error · 500~511
500	Internal Server Error	5xx Server Error	Unexpected server-side failure.	Unhandled exceptions
501	Not Implemented	5xx Server Error	Feature not implemented.	Unsupported endpoint capability
502	Bad Gateway	5xx Server Error	Invalid response from upstream.	Proxy or gateway upstream errors
503	Service Unavailable	5xx Server Error	Service temporarily unavailable.	Maintenance or overload
504	Gateway Timeout	5xx Server Error	Upstream timed out.	Dependency timeout propagation
505	HTTP Version Not Supported	5xx Server Error	HTTP version not supported.	Legacy protocol rejection
507	Insufficient Storage	5xx Server Error	Server cannot store representation.	Storage quota exhaustion
508	Loop Detected	5xx Server Error	Infinite loop detected during processing.	Recursive WebDAV operations
510	Not Extended	5xx Server Error	Further extensions required.	Extension policy requirements
511	Network Authentication Required	5xx Server Error	Network authentication required.	Captive portal environments

What is HTTP?

HTTP (Hypertext Transfer Protocol) is the request-response protocol used by browsers, mobile apps, and APIs to communicate with web servers.

A client sends a request (method, URL, headers, body), and the server returns a response (status code, headers, body). The status code is the first signal that tells clients whether the request succeeded, failed, or should be redirected.

In production systems, correct status codes improve caching, retry logic, monitoring, SEO behavior, and developer debugging speed.

How to read HTTP status code classes

1xx · Informational

Request received, processing continues.

2xx · Success

Request completed successfully.

3xx · Redirection

Client should perform another request to a different URL.

4xx · Client Error

Request is invalid or unauthorized from client side.

5xx · Server Error

Server failed to process a valid request.

Response examples by code

200 OK (JSON API)

HTTP/1.1 200 OK
Content-Type: application/json

{
  "id": "user_123",
  "name": "Alex",
  "email": "[email protected]"
}

404 Not Found

HTTP/1.1 404 Not Found
Content-Type: application/json

{
  "error": "RESOURCE_NOT_FOUND",
  "message": "User does not exist."
}

429 Too Many Requests

HTTP/1.1 429 Too Many Requests
Retry-After: 60
Content-Type: application/json

{
  "error": "RATE_LIMITED",
  "message": "Try again after 60 seconds."
}

Common implementation mistakes

Returning 200 for every API response hides failures from clients. Use semantically correct status codes so retries, alerts, and analytics behave correctly.

Confusing 401 and 403 is another common issue. Use 401 for authentication failures and 403 for authorization denial after identity is known.

Use 429 for rate limiting and include backoff hints where possible. Avoid masking upstream gateway failures (502/504) as generic 500 errors.