Which nine SEO risks come with a website migration?

Most people know that a relaunch can hurt SEO performance. What exactly the dangers are is less clear. Here are the nine most important SEO problems a migration can cause. If you avoid them, chances are good that you will not lose organic traffic in your migration.

The nine risks at a glance

1. What happens when content goes missing?

It sounds obvious, but it still needs saying. Content that brings organic traffic today stops bringing it after the migration if you delete it. So check which content brings traffic today and plan it into the new concept. How to do that is explained in the guide Important content in a website migration.

A relaunch is often seen as a good opportunity to get rid of old content. Honestly, we often only want to delete old content because we no longer feel like maintaining it. Use the migration to refresh it instead. If something is out of date, rework it until it is interesting again. Your SEO performance will thank you.

2. Why are redirects the biggest risk?

Missing, incomplete or faulty redirects are among the most common SEO mistakes in a migration and probably the most typical reason for traffic losses afterward.

If URLs change, every old URL needs a 301 redirect to a new URL with equivalent content. If these redirects are missing, incomplete or wrong, you lose organic traffic. Even if you feel well prepared, a lot can go wrong. Wrong status codes, wrong targets, redirect chains and redirects to the home page are common. Google treats many redirects to an irrelevant target as soft 404s. According to Google, keep the redirects for as long as possible, generally at least one year.

How to test redirects systematically before and after go-live is explained in the guide Testing redirects.

3. How do fewer internal links affect you?

Internal linking usually gets less attention and works more subtly than the previous points. Google uses links to find new pages and to assess how relevant pages are. If a page loses most of its internal links in a migration, it will very likely also lose rankings and the traffic that comes with them.

On large websites, even small structural changes can cost thousands of pages thousands of internal links. After go-live, a change like that quickly leads to losses in traffic and revenue.

Eoghan Henn, co-founder of searchVIU, once worked as an external SEO consultant on the relaunch of a website that generated millions in organic revenue. The agency wanted to replace the old mega menu with a new main navigation of only six links. For usability, that may have been a good idea. From an SEO perspective, it would probably have been a disaster. The compromise was additional navigation layers, so most pages kept most of their internal links. In the end, the relaunch went well from an SEO perspective.

4. Which optimizations get lost in a migration?

When you focus on redirects and new content, it is easy to forget the basics. If optimizations on the old website improved SEO performance, they belong on the new one too.

That includes basics such as titles, meta descriptions and optimized headings. It also includes technical measures such as canonical tags against duplicate content, hreflang for international websites and structured data. After a move, every new URL points to itself with its canonical, and hreflang points to the new URLs.

All optimizations from recent years belong on the new website. So check the new website thoroughly before go-live, for example with an SEO audit.

5. Which technical errors are dangerous in a migration?

One of the worst outcomes of a migration is a new website that cannot be crawled or indexed because of technical errors. It happens more often than you might think. Typical cases are a noindex left over from development, a robots.txt that blocks everything or password protection that goes live.

Crawl the new website before and right after go-live with a suitable tool to find such traps for search engine bots. How to check your staging environment without it ending up in the index is covered in the guides SEO check before go-live and Staging environment and SEO.

6. What happens to backlinks pointing to old URLs?

Also pay attention to links from other websites during a migration. Sometimes content with backlinks simply disappears or moves to a new URL without a redirect.

That hurts for several reasons. The linking website points to a page that no longer exists. Users do not find what they are looking for and land on a 404 page. Your SEO performance suffers too, because a link to an error page does little for you.

Ideally, content with backlinks stays reachable at the same URL on the new website. If the URL has to change, redirect the old URL cleanly to the new target. If the content cannot stay in the same form, design the target so it meets the expectations of users who arrive through the link. Google also recommends asking the linking websites to update their links.

7. Why is mobile rendering a risk of its own?

Rendering on mobile devices is often overlooked in migrations. That is riskier today than it used to be, because Google indexes and ranks websites using the mobile version fetched by the smartphone Googlebot. If content, links or structured data are missing from the mobile version, they are missing for Google.

This matters most when a website with separate mobile URLs, such as m.example.com, switches to a responsive design. Then the old mobile URLs need their own redirects too, and those are easily forgotten. Use tools that crawl your website like the mobile Googlebot and analyze the results.

8. What changes with content rendered by JavaScript?

A few years ago, you could assume that search engines did not see content created by JavaScript. Today Google renders JavaScript with a current version of Chromium. Content from JavaScript therefore belongs in the comparison between the old and new website. If content or links that the old website generated via JavaScript disappear, that can cost traffic.

It also works the other way around. If text and links on the new website only appear via JavaScript, Google sees them only after rendering. Many AI crawlers do not execute JavaScript and only see the source code. More on this in the guide AI crawlers.

9. What does a domain change cost?

Migrations with a domain change are special cases. A domain change without any other changes to the website also deserves special attention. It almost always costs organic traffic temporarily, at least when the content moves to a completely new domain. If it moves to an already established domain, this effect may not occur.

With a domain change, you basically have the same SEO tasks as with any other migration. The difference is that you will most likely lose some traffic temporarily even if everything goes well and no mistakes are made. A domain change therefore only pays off if you expect better SEO performance from the new domain in the long run.

For the switch, Search Console offers the Change of Address tool. It only works at the domain level and stays in effect for 180 days. There, Google recommends keeping the redirects for at least 180 days, and longer as long as old URLs still get traffic from Google Search. Google's site move guide says at least one year. We recommend going by that year. An example of moving several country domains to one domain is shown in the guide From ccTLDs to one gTLD.

How do you check the nine risks?

• Take important content with you to the new website
• Set up 301 redirects completely and correctly
• Keep or improve internal linking
• Carry over all existing on-page optimizations
• Check the new website thoroughly for technical issues before go-live
• Keep an eye on inbound links
• Watch for changes in mobile rendering
• Include content and links from JavaScript in the comparison
• Plan for the additional risk of a domain change

The order of all tasks before, during and after go-live is in the website migration checklist. To give SEO enough weight in the project, a traffic forecast for project management and leadership helps.