A website relaunch should be a step forward, yet it is one of the riskiest events in a site's life. Change domains, platforms or page structure without a plan and rankings built over years can vanish in a week. Website migration SEO is the discipline that prevents that: an audit, a redirect map and a set of launch checks that carry your authority from the old site to the new one. This guide is the checklist we use, written so you can follow it whether you are rebuilding, replatforming or moving domains.
What counts as a migration, and why rankings are at risk
A site migration is any change that alters your URLs, structure or platform: a redesign or rebuild, a move between content management systems, a domain change, merging two sites into one, or a major restructure of categories. The risk mechanics are the same in every case. Google's understanding of your site is attached to specific URLs. Years of links, history and trust point at those addresses, and brand-new URLs start with none of it. When an old URL disappears without forwarding its visitors and its equity to a successor, that value is stranded. Most stories that begin with "the redesign killed our traffic" are not really about the design at all. They are about missing redirects.
Not every migration carries equal risk. A domain change is the deepest cut, because every signal has to move; it also gets extra help, in the form of Search Console's change-of-address tool, which you should use alongside the redirects. A replatform that keeps URLs identical is the gentlest, and worth engineering for if you can. Most projects sit in between: same domain, new structure, and success decided almost entirely by how well the old URLs are mapped to the new ones.
Before the move: crawl, benchmark, map
Preparation is most of the job, and it starts with a complete inventory. Crawl the current site so you hold a full list of every URL that exists. Then pull the performance picture from Google Search Console and your analytics: which pages earn traffic, which queries they rank for, and which URLs have links pointing at them. That data decides what the new site must protect, because the pages quietly earning your rankings are rarely the ones anyone remembers in a redesign meeting. Benchmark everything, rankings, traffic and top pages, so post-launch comparisons are honest. Finally, decide the fate of every URL: kept, merged into a stronger page, or deliberately retired.
Two disciplines make the preparation stick. Freeze content changes for the migration window, because rewriting pages at the same time as moving them makes any post-launch drop impossible to diagnose: move first, measure, then improve. And test the whole redirect map on staging before launch day, crawling the old URL list against the staging site so mapping errors are found while they are still free to fix.
The redirect map: the step that saves your rankings
The redirect map is the heart of website migration SEO: a one-to-one list pairing every old URL with its closest equivalent on the new site, implemented as permanent 301 redirects. Relevance is the rule. An old service page should point to the matching new service page, not to the homepage; blanket-redirecting everything to the homepage is one of the most common and most damaging shortcuts, because it tells Google the specific page no longer has a successor. Keep each redirect to a single hop, fold in any redirects surviving from previous migrations so chains do not stack up, and have the map reviewed before launch day, not after.
How long do redirects stay? Google's guidance is to keep them live for at least a year so signals fully transfer. Our practice is to keep migration redirects permanently: old links keep pointing at old URLs for years, and a working redirect keeps collecting that value.
Launch day: the checks that catch disasters
A handful of checks, run in the first hours, catch almost every migration disaster. Confirm the new site is not blocking search engines, because a noindex tag or a robots.txt block carried over from staging is the classic self-inflicted wound. Crawl your old URL list and verify every address 301s to the right destination. Check canonical tags point at the new URLs, submit the fresh XML sitemap in Search Console, and confirm analytics is recording on the new site. Spot-check your most valuable pages against the old versions: titles, headings and content should have travelled intact, and internal links should point at final URLs rather than through redirects. Then run a full crawl against our technical SEO checklist to sweep up the rest.
After launch: monitor for weeks, not days
A site migration is not finished at launch. Google has to recrawl and re-evaluate the site, and some movement while that happens is normal. Watch Search Console daily in the first weeks: the coverage reports surface 404s and crawl errors, which usually mean a URL missed the redirect map, and the performance report shows the new URLs taking over from the old. Keep re-crawling the old URL list on a schedule, because stragglers surface late. Rankings and traffic should stabilise as the re-evaluation completes; a sustained slide is a signal to dig, not to wait.
Compare fairly while you watch. Measure the new site against the benchmarks you recorded before the move, on the same queries and the same pages, and account for seasonality before drawing conclusions: a quiet fortnight that happens every winter is not evidence the site migration failed. What you are looking for is the trend line rejoining its old path, then passing it, because a well-executed relaunch on a faster, better-structured site should end up ahead of where it started, not merely level.
If traffic dips anyway
Triage in order of likelihood. Missing redirects first: the 404 report names the stranded URLs, and fixing them recovers value fast. Content changes second: compare losing pages against their old versions, because a page that was thinned, merged or rewritten during the rebuild may simply answer the query less well than it used to. Structure third: if sections moved deeper into the site or internal links thinned out, important pages may have lost prominence. This is also the argument for doing website migration SEO properly the first time, with search built into the web design process from day one rather than bolted on after launch. And if a relaunch has already gone wrong, that is recoverable too: our technical SEO work starts with exactly this triage.
Planning a rebuild, replatform or domain change? Talk to us before you launch. A migration plan costs a fraction of a recovery project.
