How to use it
- Type a code such as 404, a class such as 4xx, or words from a name such as not found into Status code or words.
- Read Result, Meaning and Cached by default. When several codes match, the Matching codes table lists them.
- Open All registered codes to see every code in the IANA registry, with the RFC that defines it.
The five classes
The first digit of a status code gives its class, and the other two digits say which case in that class it is. RFC 9110 section 15 defines most of the codes in the registry, and each class has a fixed meaning for the client.
- 1xx Informational: the request is still in progress, and the server sends more responses.
- 2xx Success: the request was received, understood and accepted.
- 3xx Redirection: the client must take another step, usually to a different address.
- 4xx Client error: the request is wrong, or it cannot be met as it was sent.
- 5xx Server error: the server failed to handle a request that was valid.
When a response is cacheable by default
RFC 9110 section 15.1 names the codes that a cache may reuse by default, with heuristic expiration: 200, 203, 204, 206, 300, 301, 308, 404, 405, 410, 414 and 501. Every other code is not heuristically cacheable. A response with explicit cache controls follows those controls instead, so the column says what a cache does without them, not what every server does.
Where the list comes from
The table is the IANA HTTP Status Code Registry as it was on 10 November 2026: 64 registered codes. Ranges that the registry marks as unassigned are left out. Two entries need care: 104 is a temporary registration tied to an Internet-Draft, and the registry marks 510 as obsoleted. Both show a note in the result.
Worked example: 404 and not found
Typing 404 finds one code, 404 Not Found. Typing not found finds the same code, because both words start words in its name. The result is the same for both searches, and the table below shows what the tool outputs for 404.
The code is in class 4, a client error. RFC 9110 section 15.5.5 defines it, and it is one of the twelve codes that caches reuse by default.
| Output | For 404 |
|---|---|
| Result | 404 Not Found |
| Defined in | RFC 9110, section 15.5.5 |
| Cached by default | Yes: caches may store it by default (RFC 9110, section 15.1), unless the response sets other cache rules. |
Frequently asked questions
What is the difference between 401 and 403?
401 Unauthorized means the request has no valid credentials, so signing in may fix it. 403 Forbidden means the server understood the request and refuses it, so sending the same credentials again will not change the answer.
Is 410 the same as 404?
Not quite. Both say the server has no resource at that address, but 410 Gone says the resource was removed for good. RFC 9110 section 15.5.5 says the server should prefer 410 over 404 when it knows the removal is permanent.
Does a cacheable code mean the response is always cached?
No. A cache may reuse these responses by default, but a response that carries explicit cache controls, such as Cache-Control: no-store, follows those controls. Browsers and proxies also make their own choices about storage.
Why is 306 described as unused?
RFC 9110 section 15.4.7 says the value was defined by an earlier specification, is no longer used and is reserved. Software should not expect it in a response, and the table marks it as unused.
Can I invent my own status code?
You can send a number the registry does not list, but other software will not know what it means. RFC 9110 section 15.1 says new codes ought to be registered in the HTTP Status Code Registry, as section 16.2 describes.
Is my search sent anywhere?
No. The search and the table run in your browser, and nothing you type is sent to our server or stored there.
Sources
- IANA HTTP Status Code Registry
- RFC 9110: HTTP Semantics, section 15 (status codes)
- RFC 6585: Additional HTTP Status Codes
- RFC 4918: HTTP Extensions for Web Distributed Authoring and Versioning (WebDAV)
Figures and text last checked on Tuesday, November 10, 2026.