HTTP Status Codes by RFC

HTTP status codes are not defined in one place. The core set lives in RFC 9110, but many codes you meet in production — 429, 451, the WebDAV codes — were added by separate extension RFCs over two decades. This page groups every registered code by the specification that defines it, so you can see a code's provenance at a glance: which document standardized it, which section to cite, and whether it is core HTTP, an extension, a draft, or obsolete.

The groupings below follow the reference column of the IANA HTTP Status Code Registry, the authoritative source of truth. For the same codes grouped by class (1xx–5xx) instead, see the complete status code list.

RFC 9110 — HTTP Semantics

The current core HTTP specification (June 2022), which obsoleted the older RFC 7231 / RFC 2616 series. It defines the great majority of the codes in everyday use across all five classes. Cite it as RFC 9110, Section 15.

Code	Name	Section	Guide
100	Continue	§15.2.1	Guide
101	Switching Protocols	§15.2.2	Guide
200	OK	§15.3.1	Guide
201	Created	§15.3.2	Guide
202	Accepted	§15.3.3	Guide
203	Non-Authoritative Information	§15.3.4	Guide
204	No Content	§15.3.5	Guide
205	Reset Content	§15.3.6	Guide
206	Partial Content	§15.3.7	Guide
300	Multiple Choices	§15.4.1	Guide
301	Moved Permanently	§15.4.2	Guide
302	Found	§15.4.3	Guide
303	See Other	§15.4.4	Guide
304	Not Modified	§15.4.5	Guide
305	Use Proxy	§15.4.6	Guide
306	(Unused)	§15.4.7	Guide
307	Temporary Redirect	§15.4.8	Guide
308	Permanent Redirect	§15.4.9	Guide
400	Bad Request	§15.5.1	Guide
401	Unauthorized	§15.5.2	Guide
402	Payment Required	§15.5.3	Guide
403	Forbidden	§15.5.4	Guide
404	Not Found	§15.5.5	Guide
405	Method Not Allowed	§15.5.6	Guide
406	Not Acceptable	§15.5.7	Guide
407	Proxy Authentication Required	§15.5.8	Guide
408	Request Timeout	§15.5.9	Guide
409	Conflict	§15.5.10	Guide
410	Gone	§15.5.11	Guide
411	Length Required	§15.5.12	Guide
412	Precondition Failed	§15.5.13	Guide
413	Content Too Large	§15.5.14	Guide
414	URI Too Long	§15.5.15	Guide
415	Unsupported Media Type	§15.5.16	Guide
416	Range Not Satisfiable	§15.5.17	Guide
417	Expectation Failed	§15.5.18	Guide
418	(Unused) — “I'm a Teapot”	§15.5.19	Guide
421	Misdirected Request	§15.5.20	Guide
422	Unprocessable Content	§15.5.21	Guide
426	Upgrade Required	§15.5.22	Guide
500	Internal Server Error	§15.6.1	Guide
501	Not Implemented	§15.6.2	Guide
502	Bad Gateway	§15.6.3	Guide
503	Service Unavailable	§15.6.4	Guide
504	Gateway Timeout	§15.6.5	Guide
505	HTTP Version Not Supported	§15.6.6	Guide

RFC 6585 — Additional HTTP Status Codes

A short 2012 RFC that added four widely used codes, most notably 429 Too Many Requests for rate limiting. These were defined outside the core spec and remain in RFC 6585.

Code	Name	Section	Guide
428	Precondition Required	§3	Guide
429	Too Many Requests	§4	Guide
431	Request Header Fields Too Large	§5	Guide
511	Network Authentication Required	§6	Guide

RFC 4918 — WebDAV

The Web Distributed Authoring and Versioning extension. It introduced several codes for collection and locking semantics that some general APIs also reuse — 423 and 207 in particular.

Code	Name	Guide
207	Multi-Status	Guide
423	Locked	Guide
424	Failed Dependency	Guide
507	Insufficient Storage	Guide

Note: 422 Unprocessable Content originated in WebDAV but was moved into the core spec and is now defined by RFC 9110 §15.5.21.

RFC 5842 — Binding Extensions to WebDAV

Code	Name	Guide
208	Already Reported	Guide
508	Loop Detected	Guide

Single-code and niche RFCs

Several codes each come from their own focused specification:

Code	Name	Defining RFC	Guide
103	Early Hints	RFC 8297	Guide
226	IM Used	RFC 3229	Guide
425	Too Early	RFC 8470	Guide
451	Unavailable For Legal Reasons	RFC 7725	Guide
506	Variant Also Negotiates	RFC 2295	Guide

Deprecated, obsolete, and draft codes

A few codes carry special status in the registry and are worth flagging explicitly:

Code	Name	Status	Guide
102	Processing	Defined by RFC 2518; deprecated for general use	Guide
104	Upload Resumption Supported	IETF draft (not yet a final RFC)	Guide
510	Not Extended	RFC 2774 — marked OBSOLETED in the registry	Guide

Unassigned codes

Some numbers in the registry have no assigned meaning. A compliant client treats an unrecognized code as the x00 of its class (e.g. an unknown 4xx behaves like 400). If you see one of these in production, it is almost always a custom or misconfigured signal — see the guide for what to use instead.

Code	Status	Guide
427	Unassigned	Guide
430	Unassigned	Guide
509	Unassigned	Guide

Standards reference

Groupings follow the reference column of the IANA HTTP Status Code Registry, the authoritative source for status code assignments. Core definitions are in RFC 9110. Human-readable guidance by ErrorLookup. · Browse all codes by class →