A before, during and after checklist for website migrations: URL inventory, 301 redirect maps, launch-day checks and the monitoring that catches ranking losses early, plus why agencies miss items.
Short answer: a website migration keeps its SEO when every old URL that matters redirects with a 301 to its closest new equivalent, the content, titles and internal links on key pages survive the move, the new site is crawlable on launch day, and someone watches Search Console closely for the following weeks. Almost every migration disaster traces back to a skipped item below.
The risk depends on what changes:
| Migration | What changes | Risk |
|---|---|---|
| HTTP to HTTPS | Protocol only | Low |
| Platform change, same URLs | CMS or builder | Low to medium |
| Redesign with new URL structure | URLs, templates, content | Medium to high |
| Domain change | Every URL | High |
| Several at once (new domain + platform + structure) | Everything | Highest |
If you can, avoid doing everything at once. Changing domain and URL structure and content in the same launch makes it very hard to tell what caused a drop.
1. Benchmark current performance. Export 16 months of Search Console data (queries and pages), and record organic sessions and conversions by landing page from your analytics. You need a baseline to compare against.
2. Build a complete URL inventory. Combine three sources, because each misses things:
The CMS page list alone is not enough. It misses old campaign pages, PDFs, image URLs and pages that were deleted but still have links.
3. Mark your priority pages. Sort the inventory by organic clicks, conversions and referring domains. The top pages get individual attention throughout.
4. Save the old site's on-page data. Titles, meta descriptions, H1s, canonical tags, structured data and internal link counts for priority pages. Crawl tools can export all of this.
This is the single most important deliverable. It is a spreadsheet with two columns, old URL and new URL, covering every URL from the inventory.
Rules:
Test the map on staging by running the old URL list through a crawler in list mode and checking that each returns one 301 to the expected destination with a 200 at the end.
Run this in order, ideally at a quiet traffic time:
Days 1 to 14: check Search Console every day for crawl errors, 404 spikes and indexing issues. Look at server logs if you have them to see Googlebot hitting old URLs and following redirects.
Weeks 2 to 8: compare clicks and impressions by page against your baseline. Some movement is normal. A priority page that has dropped sharply and stays down needs checking: redirect correct, content intact, internal links present.
Ongoing: keep redirects in place for at least a year per Google's guidance, and preferably indefinitely. Reach out to the sites behind your most valuable backlinks and ask them to update the URL.
The query "why do agencies miss key items on their SEO checklist during website migrations" gets asked for a reason. The recurring causes:
Prevention is procedural: involve SEO when the sitemap is being planned, make the signed-off redirect map a launch requirement, add "robots and noindex check" to the deploy steps, and assign a named person to monitoring for the first month with a written rollback or fix plan.
If you are migrating because your current platform is hard to maintain, choose a destination where you control URLs, titles and redirects yourself. We.Inc lets you rebuild pages from a chat description and then adjust them visually or in code, with hosting and SSL included, so you can keep your existing URL structure. Before launch, run the new pages against our on-page SEO checklist and make sure tracking is in place with the analytics setup guide.
Some temporary fluctuation is normal while Google recrawls and processes redirects. Lasting losses almost always come from preventable problems: missing redirects, removed content, blocked crawling, or changed titles and internal links. A careful migration usually recovers within weeks.
Use permanent redirects (301 or 308) for pages that have moved for good. Temporary redirects (302 or 307) tell search engines the old URL may come back, which is not what you want in a migration.
Google's guidance is to keep redirects for at least a year, and in practice keep them indefinitely where you can, because old links, bookmarks and emails keep sending visitors to the old URLs.
Only when you move to a new domain. After redirects are live, use the Change of Address tool in the old domain's Search Console property. It is not used for moving URLs within the same domain or switching from HTTP to HTTPS.
Usually because SEO is brought in after the build is finished, the URL inventory comes from the CMS instead of a crawl plus analytics and backlink data, and nobody owns post-launch monitoring. Fix it by making the redirect map a sign-off item before launch and assigning a named person to check Search Console daily for two weeks.
How we research, test and update this page: our editorial policy. We.Inc is our own product.
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