HTTP Status Lookup

404 Not Found — 4xx Client Error.

How it works

• Matched the exact code 404 in the RFC 9110 registry.
• Read its class (4xx Client Error) and description.

• The phrase is the registered reason phrase; servers may send a different one, which is not significant.

Methodology

1. Match a purely numeric query against the registry by exact code.
2. Match a text query case-insensitively against the reason phrase, class label and description.
3. Return the full registry for an empty query.
4. Reject a numeric value that is not a three-digit code between 100 and 599.

Usage

1. Type a three-digit status code for an exact lookup, or a phrase such as "not found".
2. Leave the box empty to list the whole registry.
3. Read the reason phrase, class, description and reference.

Examples

These are examples, not current values: they use fixed inputs, while the interactive tool computes live results in your browser.

Exact 404

{
  "query": "404"
}

Text search

{
  "query": "timeout"
}

Informational class

{
  "query": "103"
}

Limitations

Classes, not individual codes

The first digit of a status code identifies its class, and a client can act on the class alone. 2xx means success, 3xx means the client must take another step, 4xx means the request as sent is at fault, and 5xx means the server failed. Individual codes refine that meaning, but a client that only handles a handful of codes is still correct if it handles the class.

Codes people misread

401 means unauthenticated (you have not proven who you are) while 403 means authenticated but not allowed. 301 and 308 are permanent; 302 and 307 are temporary, and 307/308 preserve the method while 301/302 historically changed it. 418 is an April Fools' code, and 451 reports a legal restriction.