The Website Migration Checklist for Advertisers: How to Not Break Your Running Ads

Why Migrations Break Ads

The destination URL in an ad is static text. When your site changes its URL structure (a new CMS, new categories, new slugs, a domain move), the old URL inside the ad does not change with it. The ad platform knows nothing about your migration and has no reason to pause the ad. If the old URL redirects nowhere, every click from that moment lands on an error page.

What makes it treacherous is the scale: an ordinary mistake breaks one ad, a migration can break all of them at once. And it usually happens on a Friday evening, when the new version of the site goes live.

Before the Migration

1. Take inventory of your ad URLs. Export the destination URLs of every active ad across all campaigns (including paused ones you plan to reactivate). This is the list of addresses the new site must serve.
2. Prepare a redirect map. For every old URL, define a permanent redirect (301/308) to its closest equivalent on the new site. Google recommends exactly this for SEO during site moves with URL changes.
3. Verify redirects preserve query parameters. UTM parameters and click IDs must carry over to the target URL, or you lose conversion tracking even though the page works.
4. Do not forget the Meta Pixel and tracking code. A new template system often means the pixel needs reinstalling. Without it, landing page views and conversion optimization stop working.

During and Right After the Migration

1. Walk your ad URL list and test each one. Not the homepage, the exact URLs from your ads, parameters included. An incognito window and a few minutes of discipline is all it takes.
2. Check the SSL certificate of the new infrastructure. New hosting or a new proxy means a new certificate and a new auto-renewal setup that needs verifying.
3. Watch your metrics for the following days. A drop in the landing-page-views-to-clicks ratio is the first symptom that some URL stayed broken.
4. Let automation guard the URLs. A manual post-migration check is a one-off, but redirects and pages keep breaking for weeks afterwards. 404Watcher checks every active ad URL hourly, so the late breakage gets caught for you.

Key Takeaways

• Ad URLs are static: the site changes, the ads do not. A URL inventory before migration is the foundation.
• Every old URL needs a permanent redirect that preserves UTM parameters.
• Checking on migration day is not enough: things keep breaking for weeks. Hourly monitoring is the only reliable safety net.

Sources

• Google Search Central: Site Moves With URL Changes
• MDN Web Docs: Redirections in HTTP
• Meta Business Help Center: About URL Parameters