A 301 redirect is the server's way of saying "this page has moved permanently, go here instead". Anyone who visits the old address, whether a person, a bookmark or a search engine, is sent to the new one automatically. It is the standard tool for keeping old links working after you change a URL.
What the server actually sends
When a browser requests the old URL, the server replies with status code 301 Moved Permanently and a Location header holding the new address. The browser then requests that address. Browsers cache 301s aggressively, so they may skip the old URL entirely on later visits.
For search engines, a 301 is a strong signal that the target should replace the old URL in the index. Google has said redirects of the 3xx type do not lose PageRank, so links pointing at the old page continue to count for the new one. A close cousin, 308 Permanent Redirect, means the same thing but forbids changing the request method, and Google treats it the same as a 301.
A redesign that keeps its rankings
A plumbing firm rebuilds its site. The old boiler page lived at /services.php?id=4; the new one is /boiler-repair. Before launch they list every old URL that gets traffic or has links pointing to it (Search Console's Pages and Links reports help), then add one 301 per old page to its closest new match. The old directory listings, Google results and printed leaflets all still land on the right page.
When your site needs a permanent redirect
You need 301s whenever a URL changes for good: a renamed page, merged pages, a move from http to https, from www to bare domain, or a switch to a new domain. If the change is temporary, such as a holiday closure page, use a 302 redirect instead. Pointing one whole domain at another at the registrar is domain forwarding, which should also be set to permanent.
301 redirect mistakes
- Redirecting everything to the homepage. Google treats irrelevant redirects like a 404, and visitors lose the page they wanted.
- Chains: A to B to C. Update old redirects to point straight at the final URL.
- Leaving internal links on the old URLs. Update your own menus and links rather than relying on redirects.
- Removing redirects too soon. Keep them at least a year; Google suggests that as a minimum, and longer is safer.
Related terms
- 302 redirect: the temporary counterpart.
- Canonical tag: a softer way to consolidate duplicates without redirecting.
- URL: the address a redirect changes.
- Domain forwarding: redirecting an entire domain.