Changing CMS is the migration type where URLs change because the platform insists, not because anyone chose to change them. That single fact drives most of the risk and most of the work.
What makes a platform change different
- The new platform imposes URL patterns. Most CMSs have opinions about paths, and not all of them are configurable.
- Templates are rebuilt, not ported. Headings, metadata and internal links are reconstructed, and things get dropped.
- Content is transformed on import. Formatting, embeds and structured content frequently degrade.
- Plugin behaviour does not transfer. Redirects, schema and sitemap logic all live in tools that may not exist on the other side.
It is simultaneously a URL migration and a redesign, which is why it carries the risks of both. See website redesign SEO.
Before committing to a platform
- Confirm you can control URL structure, or accept that every URL changes.
- Confirm you can set titles, meta descriptions, canonical tags and robots directives per page.
- Confirm redirects can be managed at scale, not one at a time through an interface.
- Confirm the sitemap is generated and controllable.
- Confirm server-rendered HTML, or understand the rendering implications. See JavaScript SEO.
These are cheap to verify before signing and expensive to discover afterwards.
Sequence
- Crawl and export everything from the current site — URLs, titles, metadata, word counts. This is your baseline and your verification list.
- Export Search Console data, since it establishes which pages actually matter.
- Build the new site on staging, blocked from crawling, and confirm the block is removable. See staging site SEO.
- Map URLs one to one before launch, not after.
- Compare staging against the old crawl page by page — titles, headings, word counts, internal links. This single check catches most damage.
- Launch with redirects already live.
- Verify immediately: robots.txt, noindex, canonicals, sitemap.
Step five is the one that gets skipped under deadline pressure and the one that matters most.
What reliably goes wrong
- Metadata not carried across, so a plugin generates templated titles for the whole site.
- Content truncated on import, particularly long pages and tables.
- Old redirects lost, breaking paths that had worked for years.
- Internal links pointing at old URLs, routing every click through a redirect.
- Staging directives shipped live.
Frequently asked questions
Can I keep my URLs?
Sometimes, and it is the single most valuable thing to preserve. Where the platform allows it, do it — it removes most of the risk.
Should I redesign at the same time?
It is efficient and it makes diagnosis much harder, because you cannot tell which change caused a problem. Separate them if you can.
How long before traffic stabilises?
Typically weeks, longer for large sites. See SEO migration timeline.
Who should run it?
Developers build it; someone needs to own the URL mapping and verification. Those are different jobs and both are required.
Consulting CTA
If a platform change is planned, book an SEO consultation before the build starts, while URL decisions are still open.