A site migration is like moving a house while the family’s still inside and dinner’s on the stove. The lights need to work, the fridge stays cold, and the neighbors still know where to find you. Google’s one of those neighbors, and if you confuse it, you’ll lose trust, rankings, and revenue overnight. The biggest mistake businesses make? Thinking a migration is just swapping in a shiny new design. It’s not. It’s a high-stakes operation to make the site better without breaking the business.
Google’s own documentation is blunt: migrations can hurt if you don’t plan. Miss a few redirects or mess up your URL structure and you can watch years of SEO authority vanish. The best SEO agencies don’t leave this to chance: they follow a playbook.
Crawl Before You Touch Anything
The first move is a full crawl of the current site. Tools like Screaming Frog and Ahrefs grab every URL, metadata tag, internal link, and canonical. This isn’t just “keeping a backup.” It’s your before-and-after blueprint. Agencies also pull Google Analytics and Search Console data. If traffic tanks later, you’ll know exactly where to look. Without it, you’re flying blind.
Redirects Make Or Break The Migration
The redirect map is the backbone of any safe migration. Every single old URL gets a one-to-one 301 redirect to its new counterpart. No lazy wildcard rules, no 302s, no redirect chains that waste crawl budget and bleed link equity. Ahrefs has seen bad redirect setups cost sites 40% of traffic overnight. Search Engine Journal warns the same: get this wrong and it’s a revenue killer.
Test the Staging Site Like Google Would
Good agencies don’t trust a site just because it “looks good.” They crawl the staging site to catch blocked pages, robots.txt mistakes, wrong canonicals, or broken links. And staging always stays blocked from search. Google warns that an open staging site can create duplicate content problems instantly.
Use the Migration to Clean House
Migrations are the perfect excuse to prune and consolidate. Thin content, outdated posts, and duplicates get cut or merged. The result? A leaner, stronger site where authority flows to the pages that matter most.
Speed Is Non-Negotiable
If your new site loads slower than your old one, you’ve failed. Core Web Vitals are a ranking factor, and Google has been vocal about it. The best agencies benchmark performance before launch and fix anything that slips. Search Engine Land has shown that slow migrations can undo months of SEO gains.
Watch It Like a Hawk After Launch
The migration isn’t over when the site goes live. Agencies crawl the live site again, check Search Console for errors, and track 404s in real time. Some traffic dip is normal. Big drops mean trouble. Google even has a Change of Address tool for this exact reason, and top agencies use it.
What Happens If You Don’t
Plenty of horror stories. One case on the Google Help Forum shows a business losing 90% of its traffic because they did not do correct redirect mapping. Compare that to a proper migration where traffic barely dips and recovers in weeks. The difference is planning.
The Bottom Line
Site migrations are not design projects with a few SEO tweaks. They’re SEO projects with design and dev wrapped around them. The agencies that do it right follow a process: benchmark, redirect map, staging checks, content consolidation, performance audits, and relentless post-launch monitoring.
Looking for someone who knows how to handle site migrations inside out? See our list of verified SEO services agencies here.