Why backlinks matter during a website migration

A migration changes page addresses: new CMS, new structure, sometimes a new domain name. The sites that link to you change nothing: their links keep pointing to the old addresses. The whole point is that these links still lead somewhere after go-live.

• Popularity: a link from another site is a signal of trust that Google takes into account to rank pages; this is the PageRank principle, covered in our article on PageRank and migration.
• Traffic: visitors arrive through these links, independently of Google.
• Page discovery: robots follow links; a page linked from outside is found and revisited faster.

These links often represent years of relationships, syndicated content and link-building budget: they are not rebuilt in a few weeks.

When the URL a link points to returns a 404 after the migration, the link passes nothing on: the page loses the popularity it brought, the visitor lands on an error, and Google eventually drops the old address from its index without carrying its value over. A 301 redirect to the page that takes over the content tells Google that the address has changed, and it carries its signals over to the new one.

Two mistakes cancel part of this transfer: redirecting to the home page rather than to the equivalent page, which Google may treat as a soft 404; and chaining redirects, when an old redirect points to an address that is itself redirected. Our article on the SEO risks of redirects covers them in detail.

The home page rarely changes address. The exposed pages are the others: an article quoted by the media, a product page picked up by a comparison site, a guide linked from forums, and above all the pages the site no longer shows (removed from the menus, deleted in an earlier redesign) but which still receive links. They do not appear in a crawl: only backlink tools reveal them. Our article on backlink tools explains how to list them, and should you redirect every URL that receives links answers the question of which pages to keep.

When the domain changes, every address changes, including the home page's: every link to the site then depends on a redirect. Keep the old domain and its redirects for as long as possible; see should you renew the old domain name and how long to keep a redirect.

1. List the pages of the old site that receive links, using several sources.
2. Give each one a 301 redirect to the page of the new site that takes over its content.
3. Test these redirects on staging, then in production on go-live day: each old URL must lead in a single hop to a page that returns 200.
4. For the most valuable links, ask the sites that make them to point directly to the new address.

Swan handles the first three steps: it imports the URLs exported from your backlink tools with their origin, suggests the closest page of the new site for each one, and checks the redirects on staging and then in production. A step-by-step example with Majestic and Swan.