301 3xx RFC 9110 §15.4.2

Moved Permanently

Resource has permanently moved to the URL in the Location header. Subsequent requests should use the new URL.

What HTTP 301 means

RFC 9110 §15.4.2. SEO-significant: search engines transfer ranking signals on 301. Some clients change POST to GET on follow; use 308 to preserve the method.

Typical causes

Permanent URL change
HTTPS upgrade redirect
Domain migration