301 or 308 - which should I use?

308 if the request might not be a GET, because it guarantees the method and body are preserved. 301 is permitted to turn a POST into a GET, and nearly all clients do, silently dropping the body. For permanent GET redirects, 301 is fine and has the broadest support.

301 or 302 for a site move?

301. It is permanent, so clients and search engines update their references and ranking signals transfer. A 302 tells them the move is temporary and to keep using the old URL.

Why can't I undo a 301?

Because browsers cache it, often for a very long time, and stop requesting the old URL at all. Test redirects with a temporary 302 or 307 first, then switch to 301 or 308 once you are certain.

301 Moved Permanently

The resource has permanently moved to the URL in the Location header.

Class 3xx · Redirection
Retry Safe to retry

What 301 means

301 tells clients and search engines that a resource has moved for good and that they should update their references. Browsers cache it aggressively - often indefinitely - which is the main practical hazard: a 301 published by mistake is very hard to take back, because clients stop asking.

The other hazard is method rewriting. Historically 301 and 302 permitted a client to change the request method to GET when following the redirect, and virtually all of them do. A redirected POST therefore arrives as a GET with no body, which loses the request silently.

For that reason, use 308 rather than 301 whenever the request might not be a GET. 308 has identical caching semantics and guarantees the method and body survive. 301 remains fine for GET-only redirects and is understood by every client ever written.

For SEO, a 301 passes ranking signals to the new URL and is the correct way to consolidate duplicate URLs or move a site.

Headers this status expects

Location - the new URL. Required; a 301 without it is meaningless.

Should a client retry?

Follow the redirect to the Location URL. Clients do this automatically.

FAQ

301 or 308 - which should I use?: 308 if the request might not be a GET, because it guarantees the method and body are preserved. 301 is permitted to turn a POST into a GET, and nearly all clients do, silently dropping the body. For permanent GET redirects, 301 is fine and has the broadest support.
301 or 302 for a site move?: 301. It is permanent, so clients and search engines update their references and ranking signals transfer. A 302 tells them the move is temporary and to keep using the old URL.
Why can't I undo a 301?: Because browsers cache it, often for a very long time, and stop requesting the old URL at all. Test redirects with a temporary 302 or 307 first, then switch to 301 or 308 once you are certain.

Often confused with

302 Found The resource is temporarily at a different URL.
307 Temporary Redirect Temporarily at a different URL, and the method and body must be preserved.
308 Permanent Redirect Permanently moved, and the method and body must be preserved.