3xx

3xx is a class of HTTP status codes that indicate redirection. When a client requests a resource, a server may respond with a 3xx code to signal that the requested resource can be found at a different URI. Most 3xx responses include a Location header specifying the new address; clients typically follow the redirection automatically.

Common 3xx status codes include:

- 300 Multiple Choices: the server offers several representations of the resource, and the user agent may choose one.

- 301 Moved Permanently: the resource is now permanently located at a new URI; redirects should be cached by clients and intermediaries.

- 302 Found: historically used for temporary redirects; behavior with HTTP methods has varied, leading to the introduction of more precise codes.

- 303 See Other: the client should fetch the target resource using a GET method, typically after a POST or other request.

- 304 Not Modified: not a redirect itself; indicates that a cached copy is still valid and can be used, usually in conditional requests.

- 305 Use Proxy: deprecated and no longer recommended for use.

- 307 Temporary Redirect: the resource is temporarily at a different URI; the original request method should be used for the redirected request.

- 308 Permanent Redirect: the resource has moved permanently to a new URI; the original request method should be used for subsequent requests.

Usage and implications: 3xx responses are used for URL changes, content negotiation, or resource restructuring. They interact with caching and search engine indexing; 301 and 308 are commonly favored for permanent moves, while 302 and 307 are used for temporary moves. Proper use of 3xx codes helps clients locate resources efficiently and preserves semantics across redirects.