Keep Old Domain & 301 Redirects for as Long as Possible After Domain Migration
John recommends maintaining 301 redirects from an old domain to the new one for at least a year after migrating. However, users may still access the old domain years after the migration, so consider keeping the redirects for as long as possible. Also try to keep ownership of the old domain so spammers don’t misuse it.
Performing URL Rewriting is the Best Way to Change the URL Structure of a Site
If you are changing the URL structure of a website, John recommends keeping the old URLs and rewriting the URLs on the server-side, if possible. This is because, from Google’s point of view, there is very little change and it’s easier to understand the content than having to reprocess all of the new URLs. If you are not able to keep the old URLs, ensure you 301 redirect from the old ones to the new ones. A redirect is a much stronger signal that you are moving content to new URLs than canonicalising them.
Use Crawlers to Detect Internal Links to Redirecting URLs After Migration
Use crawlers like DeepCrawl to detect internal links pointing to a redirecting URL after a migration.
URL Inspection Tool Silently Processes Redirects to Display Target Page
The URL Inspection Tool generally displays the content that Google will index rather than the entered URL. If it has a redirect, this will be silently processed and the target page will be shown instead.
Google Will Not Render JavaScript Content if The Page Returns a Redirect or Error Code
If you have a page which contains JavaScript content but it returns a redirect or an error code, Google will not spend time rendering the content. For example, if you use JavaScript on a 404 page to display an error message or links. With redirects, Google does not need to render the content in order to follow the redirect to the new page.
There is no Harm in Redirecting Parked Domains to a Live Website
If you have parked domains redirecting to your main site, for example for offline marketing purposes, there is no negative impact from an SEO perspective.
Use Redirects & Canonical Tags to Stop Data From Other Site on Same IP Being Included in GSC
If there are internal links between two sites on the same IP address, data for both sites can sometimes appear in the same GSC account. If you don’t want Google crawling the other site then add redirects or canonical tags pointing to the main site.
Implement Redirects From Mobile Pages to Desktop Pages For Desktop Users
If you have a separate m-dot site, Google will usually pick this as the preferred canonical version after mobile-first indexing and the m-dot site will be shown in desktop search results. To avoid negative UX, implement redirects to the desktop version for desktop users.
Redirects Can Impact Crawl Budget Due to Added Time for URLs to be Fetched
If there are a lot of redirects on a site, this can impact crawl budget as Google will detect that URLs are taking longer to fetch and will limit the number of simultaneous requests to the website to avoid causing any issues to the server.