How can you prevent indexing collapse during a website migration?

Why are stable redirects crucial during a migration?

When a site migrates, Googlebot needs to relearn the complete mapping of your content. Each 301 or 302 redirect serves as a signal indicating to the engine where to find the canonical version of a page.

If you change these redirects regularly, you create conflicting signals. Google doesn't know which version to index and treat as the reference. The result? Fluctuations in the index that can last for weeks or even months.

What does "not changing frequently" really mean?

Mueller remains vague about the definition of "frequently." [To be verified] In practice, observations suggest that a redirect should remain stable for at least 3 to 6 months after the complete migration.

Some sites attempt to temporarily revert to the old domain in case of technical issues or traffic drops. This strategy is exactly what Google advises against here. The engine needs consistency, not back and forth.

Do all pages really need to be redirected?

The phrase "all old pages" requires a significant nuance. This obviously refers to pages with SEO value: organic traffic, backlinks, ranking history.

Orphan pages, existing 404 errors, or duplicate content do not need to be redirected. However, each indexed URL with traffic must have a clear destination on the new site, even if it's to a category page or the homepage in extreme cases.

• Stability of redirects: Once established, do not alter them for at least 3 to 6 months
• Full coverage: Map all indexed and traffic-generating URLs before migration
• Signal consistency: Avoid any temporary switching back to the old domain
• Continuous monitoring: Monitor redirects in Search Console
• Long-term maintenance: Keep redirects for a minimum of 12 to 24 months to transfer link equity

Is this statement consistent with field observations?

Yes, but it remains dangerously vague on timelines. The failed migrations I have audited almost all follow the same pattern: a technical team adjusting redirects "on the fly" for weeks, creating the very chaos that Mueller describes.

What is lacking here is the distinction between temporary and permanent redirects. Google treats 301 and 302 differently, but Mueller doesn't specify this. 302 redirects convey less equity and signal an intent to return eventually, complicating indexing further.

What use cases does this rule not cover?

Mueller talks about complete migration, but reality is often more nuanced. Section-by-section progressive migrations (first the blog, then product categories, etc.) are not addressed. Yet, this is a common practice on large e-commerce sites.

Similarly, there's nothing about HTTPS migrations or URL structure changes without a domain change. Do the rules apply the same way? Probably, but the lack of precision leaves practitioners in the dark. [To be verified]

What critical error does this statement not mention?

The chain of redirects remains the most frequent pitfall. Old domain to temporary domain to new domain: each step dilutes link equity and slows down crawling. Google follows redirects but loses patience after 3 to 5 hops.

Another omission: client-side redirects via JavaScript. Some modern frameworks implement redirects in JS, complicating the transmission of signals. Mueller mentions "crawling these redirects," but Googlebot does not always view JS redirects the same as server-side 301 redirects.

What specific actions should you take before and during the migration?

Before any switch, map all indexed URLs using Search Console and a complete site crawl. Create an exact mapping file between old and new URLs. This document becomes the single reference for setting up redirects.

During the migration, test redirects on a representative sample before switching all traffic. Use tools like Screaming Frog to ensure that each redirect returns a clean 301 code, without chains or loops.

What mistakes should you absolutely avoid after the migration?

Do not touch the redirects once the switch is made, except in cases of clear errors (loops, 404 destination). Resist the temptation to temporarily revert to the old site if traffic drops. This drop is normal for 2 to 4 weeks while Google re-crawls and reassesses.

Avoid modifying the URL structure of the new site in the first few weeks. If you made a design mistake, live with it for at least 3 months. Stability takes precedence over immediate perfection.

How can you check if Google is handling the migration correctly?

Monitor the coverage report in Search Console. The number of indexed pages will fluctuate for a few weeks; this is normal. However, a massive increase in 404 errors or "Excluded by redirect" indicates a configuration issue.

Also, check that old URLs are not still indexed beyond 4 to 6 weeks. Use site:old-domain.com searches to identify pages that Google has not yet transitioned. If they persist beyond 2 months, it means that redirects are not being crawled properly.

• Create a complete mapping file old domain → new domain before any switch
• Implement server-side 301 redirects (not via JavaScript or meta refresh)
• Test all redirects in a staging environment before going live
• Keep the old domain active with redirects for a minimum of 12 months
• Monitor Search Console daily for the first 4 weeks post-migration
• Do not modify the URL structure of the new site for at least 3 months after switching