The most expensive mistake in a platform or design change shows up a month later: traffic has halved and the cause is now hard to reconstruct. Almost always it comes down to old URLs ceasing to exist while nobody connected them to the new ones.
The important work happens BEFORE launch
1. Inventory
A complete list of the old site's pages with their traffic and positions. Without it you cannot tell what must not be lost — nor what was lost, if something goes wrong.
2. A mapping table
Every old address gets a new one. Pages with no counterpart are decided individually: merge with another, keep as is, or retire deliberately. "Deliberately" is the key word: a page retired by decision is fine; a page retired by accident is a loss.
3. Checking the new structure
Whether headings, copy and structured data survived. Whether the new site is closed to indexing — the classic being a staging site blocked from crawlers where nobody remembered to lift the block at launch.
Launch is not the end either
- Verify the redirects genuinely work and do not form chains of several hops.
- Watch crawl errors — that is where forgotten URLs surface.
- Monitor indexation of the new pages.
- Compare traffic by section rather than as a single figure: one category dipping is invisible in the total.
Being honest about the consequences
Even with flawless preparation, a dip during the transition is normal. A search engine needs time to re-crawl the site and move signals to the new addresses. The point of preparation is to make that dip small and short. There is no such thing as zero, and promises of "no losses" deserve scepticism.
Common mistakes
Redirecting every old address to the home page instead of to its counterpart. Redirect chains after several moves in a row. Changing the URL structure "while we are at it" during a redesign, with no separate plan. Launching at the peak of the season.
Support for such a transition is the SEO support for migration or redesign service. The technical side is covered by server migration or a move to a new version. If traffic has already fallen and you need to understand why — a technical audit and duplicate removal.
