The IANA HTTP Status Code Registry contains 64 individually named HTTP response code entries ranging from 100 to 511, and each entry is grouped into one of five response classes based on its first digit: 1xx Informational, 2xx Successful, 3xx Redirection, 4xx Client Error, and 5xx Server Error. A complete HTTP response codes list is therefore not simply every three-digit number from 100 to 599 — it is the curated subset that the Internet Assigned Numbers Authority has formally registered, with each code linked to a reason phrase, a concise meaning, and a governing RFC. Standards-aligned references such as the HTTP Status Codes tool present exactly this snapshot so developers can look up a code by number, by class pattern such as 4xx, by reason phrase such as Not Found, by protocol concept such as gateway, or by RFC reference. Because status codes carry protocol semantics that affect caching, authentication, retry behavior, and security, the cited RFC remains authoritative; a paraphrase in any reference table is a starting point rather than a replacement for the specification.
The Five Response Code Classes
HTTP response codes are organized by their leading digit into five classes. The first digit alone communicates the broad category, while the full three-digit code communicates the specific protocol condition. A class is broader than one specific code: 404 Not Found and 429 Too Many Requests are both client-error responses, but they describe different conditions and usually call for different remedies.
| Class | Range | Category | Typical meaning |
|---|---|---|---|
| 1xx | 100–199 | Informational | Interim progress; the client should continue the request or ignore the response if the request is already finished. |
| 2xx | 200–299 | Successful | The request was received, understood, and accepted. |
| 3xx | 300–399 | Redirection | Further action is required to complete the request, typically by the client. |
| 4xx | 400–499 | Client Error | The request contains a condition attributed to the client. |
| 5xx | 500–599 | Server Error | The server failed to fulfill an apparently valid request. |
Within these classes, individual entries carry their own reason phrases. The 2xx class holds 200 OK, 201 Created, 202 Accepted, 203 Non-Authoritative Information, 204 No Content, 205 Reset Content, 206 Partial Content, and 226 IM Used. The 3xx class holds 300 Multiple Choices, 301 Moved Permanently, 302 Found, 303 See Other, 304 Not Modified, 307 Temporary Redirect, and 308 Permanent Redirect. The 4xx class covers request problems from 400 through 451, including 401 Unauthorized, 403 Forbidden, 404 Not Found, 405 Method Not Allowed, 406 Not Acceptable, 408 Request Timeout, 409 Conflict, 410 Gone, 411 Length Required, 412 Precondition Failed, 413 Content Too Large, 414 URI Too Long, 415 Unsupported Media Type, 416 Range Not Satisfiable, 417 Expectation Failed, 418 (unused), 421 Misdirected Request, 422 Unprocessable Content, 423 Locked, 424 Failed Dependency, 425 Too Early, 426 Upgrade Required, 428 Precondition Required, 429 Too Many Requests, 431 Request Header Fields Too Large, and 451 Unavailable For Legal Reasons. The 5xx class holds 500 Internal Server Error, 501 Not Implemented, 502 Bad Gateway, 503 Service Unavailable, 504 Gateway Timeout, 505 HTTP Version Not Supported, 506 Variant Also Negotiates, 507 Insufficient Storage, 508 Loop Detected, 510 Not Extended, and 511 Network Authentication Required.
How to Look Up a Code in the HTTP Status Codes Tool
- Enter an exact three-digit code, a class pattern such as 4xx, a reason phrase such as Not Found, a protocol concept such as gateway, or an RFC reference into the search box. Filtering happens immediately in the browser, and the search text is never uploaded to Lizely or any other service.
- Choose Informational, Successful, Redirection, Client error, or Server error from the response-class selector to narrow the matching range. The selector combines with the text query, so a phrase such as gateway under Server error returns only gateway-related server failures, while searching Not Found under Server error produces a clear empty result instead of leaving a stale table visible.
- Read the reason phrase, the concise meaning, the registration-state label, and the RFC reference for the matching entry.
- Consult the linked RFC for any decision that affects interoperability, security, caching, or automated retry behavior. The paraphrase beside each code is a practical summary, not a substitute for the specification.
What the Registry Includes and Excludes
HTTP Status Codes is built from the IANA HTTP Status Code Registry, captured on July 17, 2026. It contains 64 individual entries — every individually named row in the registry at that snapshot, including current, temporary, deprecated, unused, and obsolete codes. It excludes unassigned ranges such as the gap that contains 105, and it excludes vendor-specific extensions used by individual frameworks.
A server can return any three-digit number it likes. Because the table is registry-based rather than server-derived, a number can be syntactically shaped like an HTTP status code without appearing here. Exact numeric search is strict: entering 404 returns only 404 rather than every description containing similar digits, and entering 105 returns no row because 105 sits inside an unassigned range. The interface explains that no registered entry matched rather than truncating silently. Class patterns behave the same way. Entering 4xx selects all individually registered client-error entries; it does not fabricate rows for unassigned numbers.
Text search checks the reason phrase, the class label, the concise meaning, the RFC reference, and the registration state. Searching for gateway therefore matches 502 Bad Gateway and 504 Gateway Timeout because their meanings mention the gateway concept, while searching for Not Found under Server error produces a clear empty result rather than returning a misleading match.
Registration States Beyond "Current"
A registered code is not necessarily a current one. The IANA registry distinguishes five registration states, and the table preserves each label rather than collapsing them into a single "standard" badge.
| State | Meaning in the registry | Example in the table |
|---|---|---|
| Current | An active standard code intended for current use. | 200 OK, 404 Not Found, 503 Service Unavailable |
| Temporary | A registration tied to an active Internet-Draft that may change or expire. | 104 Upload Resumption Supported |
| Deprecated | Retained for history but not recommended for new code. | 305 Use Proxy (deprecated through RFC 9110) |
| Unused | Reserved by the registry but not assigned to any protocol meaning. | 306 (unused), 418 (unused per RFC 9110) |
| Obsolete | Superseded by another mechanism; not for current use. | 510 Not Extended |
The familiar phrase associated with 418 is not the current IANA description; the registry and RFC 9110 list 418 as unused, which is what the tool displays. Code 104 is labeled Temporary rather than silently presented as permanent, and the snapshot date is shown so a newly assigned or expired temporary code can be re-evaluated against a fresh registry pull.
Reading a Code's Meaning Correctly
The short meaning beside each code is a practical paraphrase aligned with the standard, but a response's exact semantics depend on the request method, headers, cache state, authentication context, intermediary behavior, and any extension such as WebDAV. 200 OK has method-dependent meaning: a successful GET returns the resource, a successful DELETE may carry no content, and a successful POST conveys the result of the action. 204 No Content prohibits response content by definition, which affects caching and link extraction. 304 Not Modified participates in conditional caching through If-Modified-Since and If-None-Match rather than acting as a fresh response. 401 Unauthorized concerns missing or invalid authentication credentials despite its historical reason phrase; the modern framing treats it as "unauthenticated". The linked RFC supplies the authoritative semantics for each of these cases.
Status codes communicate protocol outcomes; they do not prove the underlying cause. A 502 Bad Gateway can reflect an upstream crash, a network path problem, a proxy timeout policy, or malformed upstream output. A 429 Too Many Requests indicates rate limiting, but the retry behavior depends on the service and may use a Retry-After header. A 404 Not Found can conceal a forbidden resource, and a 500 Internal Server Error is intentionally generic. Use server logs, request identifiers, response headers, and the relevant service documentation when diagnosing a live incident. The HTTP Status Codes reference explains registered protocol meanings but does not contact a URL, inspect a server, or claim to identify an operational fault. For independent cross-checking, RFC 9110 supplies the core HTTP semantics for the standard codes, and the MDN HTTP response status codes reference provides an implementation-oriented view.