Replatforming without losing a single URL

Every replatform has the same silent risk: you rebuild the system, launch on time, and then watch organic traffic fall thirty percent because a few thousand URLs quietly changed shape. It is avoidable, and it is almost always avoided by doing boring work early.

Crawl the old site before you design the new one

Start with a full crawl and a server log export covering at least three months. You want every URL that has ever received a click or a link, not just the ones in the current sitemap. Old campaign URLs, filtered category pages and paginated views all carry equity.

Design the URL structure as a deliverable

The new URL structure is an architectural decision, not something the CMS decides for you. Agree it in the blueprint phase, together with canonical rules for filters, pagination and variants.

Build the map incrementally

1. Match one-to-one wherever the page still exists
2. Map removed pages to the closest surviving parent, never to the homepage
3. Flag anything that cannot be mapped and decide explicitly whether it should 410
4. Validate the map by crawling it in staging and asserting a single hop to a 200

Keep structured data and product IDs stable

Product feeds, ad platforms and marketplaces key off your product IDs. Change them during a migration and you reset the learning on every campaign you run. Keep the old IDs and map internally instead.

Watch the right numbers after launch

Index coverage, crawl errors and rankings for your top thousand queries, checked daily for the first two weeks. A redirect map that was correct in staging can still meet a caching layer in production that rewrites it.