ステータスコード301（リダイレクト）
HTTP Status Code 301 is a permanent redirect that automatically sends users and search engines from one URL to another. It passes 90-99% of "link equity" (ranking power) to the new URL, making it essential when migrating sites, changing URL structures, or consolidating duplicate pages.
The SEO Lifeline for URL Changes
If you change your URL structure from ?lang=fr to /fr/ without 301 redirects, you lose all your SEO history and start from zero. Every backlink, ranking signal, and indexed page becomes a dead 404. A 301 redirect tells Google "This page permanently moved here—transfer all the authority." This is critical for international expansion: when launching new language structures, migrating domains, or consolidating content, 301s preserve years of SEO investment. The alternative—302 "temporary" redirects—does NOT pass SEO value and should only be used for genuinely temporary situations.
301 Permanent vs. 302 Temporary Redirect
現実世界への影響
Site changes from mybrand.com?lang=de to mybrand.com/de
No redirects set up
German pages drop from index, traffic -100%
Implement 301 redirects from old to new URLs
Google transfers all authority to new structure
Rankings maintained, traffic recovers within 4 weeks